diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 6b99389..fec6b4c 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -9,9 +9,11 @@
 	select ARCH_NO_PREEMPT
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ASM_MODVERSIONS
 	select HAVE_UID16
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_DEBUG_KMEMLEAK
+	select HAVE_DEBUG_BUGVERBOSE
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select GENERIC_CLOCKEVENTS
@@ -31,12 +33,6 @@
 config SBUS
 	bool
 
-config PCI
-	bool
-
-config PCMCIA
-	bool
-
 config TRACE_IRQFLAGS_SUPPORT
 	bool
 	default y
@@ -85,46 +81,46 @@
 	bool
 	default y
 	depends on !LD_SCRIPT_STATIC
-        select MODULE_REL_CRCS if MODVERSIONS
+	select MODULE_REL_CRCS if MODVERSIONS
 
 config HOSTFS
 	tristate "Host filesystem"
 	help
-          While the User-Mode Linux port uses its own root file system for
-          booting and normal file access, this module lets the UML user
-          access files stored on the host.  It does not require any
-          network connection between the Host and UML.  An example use of
-          this might be:
+	  While the User-Mode Linux port uses its own root file system for
+	  booting and normal file access, this module lets the UML user
+	  access files stored on the host.  It does not require any
+	  network connection between the Host and UML.  An example use of
+	  this might be:
 
-          mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
+	  mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
 
-          where /tmp/fromhost is an empty directory inside UML and
-          /tmp/umlshare is a directory on the host with files the UML user
-          wishes to access.
+	  where /tmp/fromhost is an empty directory inside UML and
+	  /tmp/umlshare is a directory on the host with files the UML user
+	  wishes to access.
 
-          For more information, see
-          <http://user-mode-linux.sourceforge.net/hostfs.html>.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/hostfs.html>.
 
-          If you'd like to be able to work with files stored on the host,
-          say Y or M here; otherwise say N.
+	  If you'd like to be able to work with files stored on the host,
+	  say Y or M here; otherwise say N.
 
 config MCONSOLE
 	bool "Management console"
 	depends on PROC_FS
 	default y
 	help
-          The user mode linux management console is a low-level interface to
-          the kernel, somewhat like the i386 SysRq interface.  Since there is
-          a full-blown operating system running under every user mode linux
-          instance, there is much greater flexibility possible than with the
-          SysRq mechanism.
+	  The user mode linux management console is a low-level interface to
+	  the kernel, somewhat like the i386 SysRq interface.  Since there is
+	  a full-blown operating system running under every user mode linux
+	  instance, there is much greater flexibility possible than with the
+	  SysRq mechanism.
 
-          If you answer 'Y' to this option, to use this feature, you need the
-          mconsole client (called uml_mconsole) which is present in CVS in
-          2.4.5-9um and later (path /tools/mconsole), and is also in the
-          distribution RPM package in 2.4.6 and later.
+	  If you answer 'Y' to this option, to use this feature, you need the
+	  mconsole client (called uml_mconsole) which is present in CVS in
+	  2.4.5-9um and later (path /tools/mconsole), and is also in the
+	  distribution RPM package in 2.4.6 and later.
 
-          It is safe to say 'Y' here.
+	  It is safe to say 'Y' here.
 
 config MAGIC_SYSRQ
 	bool "Magic SysRq key"
@@ -147,13 +143,17 @@
 
 config KERNEL_STACK_ORDER
 	int "Kernel stack size order"
-	default 1 if 64BIT
-	range 1 10 if 64BIT
-	default 0 if !64BIT
+	default 2 if 64BIT
+	range 2 10 if 64BIT
+	default 1 if !64BIT
 	help
 	  This option determines the size of UML kernel stacks.  They will
 	  be 1 << order pages.  The default is OK unless you're running Valgrind
 	  on UML, in which case, set this to 3.
+	  It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
+	  older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
+	  increase in the size of the state which needs to be saved when handling
+          signals.
 
 config MMAPPER
 	tristate "iomem emulation driver"
@@ -185,6 +185,18 @@
 
 	  If unsure, say Y.
 
+config UML_TIME_TRAVEL_SUPPORT
+	bool
+	prompt "Support time-travel mode (e.g. for test execution)"
+	help
+	  Enable this option to support time travel inside the UML instance.
+
+	  After enabling this option, two modes are accessible at runtime
+	  (selected by the kernel command line), see the kernel's command-
+	  line help for more details.
+
+	  It is safe to say Y, but you probably don't need this.
+
 endmenu
 
 source "arch/um/drivers/Kconfig"
diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
index 2014597..85726ee 100644
--- a/arch/um/Kconfig.debug
+++ b/arch/um/Kconfig.debug
@@ -16,6 +16,7 @@
 config GCOV
 	bool "Enable gcov support"
 	depends on DEBUG_INFO
+	depends on !KCOV
 	help
 	  This option allows developers to retrieve coverage data from a UML
 	  session.
diff --git a/arch/um/Makefile b/arch/um/Makefile
index ab1066c..d2daa20 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -23,8 +23,6 @@
 # features.
 SHELL := /bin/bash
 
-filechk_gen_header = $<
-
 core-y			+= $(ARCH_DIR)/kernel/		\
 			   $(ARCH_DIR)/drivers/		\
 			   $(ARCH_DIR)/os-$(OS)/
@@ -75,7 +73,7 @@
 USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
 		$(ARCH_INCLUDE) $(MODE_INCLUDE) $(filter -I%,$(CFLAGS)) \
 		-D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \
-		-idirafter $(obj)/include -D__KERNEL__ -D__UM_HOST__
+		-idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__
 
 #This will adjust *FLAGS accordingly to the platform.
 include $(ARCH_DIR)/Makefile-os-$(OS)
@@ -116,7 +114,8 @@
 archheaders:
 	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) asm-generic archheaders
 
-archprepare: include/generated/user_constants.h
+archprepare:
+	$(Q)$(MAKE) $(build)=$(HOST_DIR)/um include/generated/user_constants.h
 
 LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
 LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie)
@@ -146,25 +145,4 @@
 	@find . \( -name '*.bb' -o -name '*.bbg' -o -name '*.da' \
 		-o -name '*.gcov' \) -type f -print | xargs rm -f
 
-# Generated files
-
-$(HOST_DIR)/um/user-offsets.s: __headers FORCE
-	$(Q)$(MAKE) $(build)=$(HOST_DIR)/um $@
-
-define filechk_gen-asm-offsets
-        (set -e; \
-         echo "/*"; \
-         echo " * DO NOT MODIFY."; \
-         echo " *"; \
-         echo " * This file was generated by arch/$(ARCH)/Makefile"; \
-         echo " *"; \
-         echo " */"; \
-         echo ""; \
-         sed -ne "/^->/{s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; s:->::; p;}" < $<; \
-         echo ""; )
-endef
-
-include/generated/user_constants.h: $(HOST_DIR)/um/user-offsets.s
-	$(call filechk,gen-asm-offsets)
-
 export HEADER_ARCH SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS DEV_NULL_PATH
diff --git a/arch/um/configs/i386_defconfig b/arch/um/configs/i386_defconfig
index 8f114e3..73e98bb 100644
--- a/arch/um/configs/i386_defconfig
+++ b/arch/um/configs/i386_defconfig
@@ -36,7 +36,6 @@
 CONFIG_CON_CHAN="pts"
 CONFIG_SSL_CHAN="pts"
 CONFIG_UML_SOUND=m
-CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
 CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y
 CONFIG_BLK_DEV_UBD=y
diff --git a/arch/um/configs/x86_64_defconfig b/arch/um/configs/x86_64_defconfig
index 5d0875f..3281d76 100644
--- a/arch/um/configs/x86_64_defconfig
+++ b/arch/um/configs/x86_64_defconfig
@@ -34,7 +34,6 @@
 CONFIG_CON_CHAN="pts"
 CONFIG_SSL_CHAN="pts"
 CONFIG_UML_SOUND=m
-CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
 CONFIG_DEVTMPFS=y
 CONFIG_DEVTMPFS_MOUNT=y
 CONFIG_BLK_DEV_UBD=y
diff --git a/arch/um/drivers/Kconfig b/arch/um/drivers/Kconfig
index 2b1aaf7..fea5a0d 100644
--- a/arch/um/drivers/Kconfig
+++ b/arch/um/drivers/Kconfig
@@ -11,58 +11,58 @@
 config SSL
 	bool "Virtual serial line"
 	help
-          The User-Mode Linux environment allows you to create virtual serial
-          lines on the UML that are usually made to show up on the host as
-          ttys or ptys.
+	  The User-Mode Linux environment allows you to create virtual serial
+	  lines on the UML that are usually made to show up on the host as
+	  ttys or ptys.
 
-          See <http://user-mode-linux.sourceforge.net/old/input.html> for more
-          information and command line examples of how to use this facility.
+	  See <http://user-mode-linux.sourceforge.net/old/input.html> for more
+	  information and command line examples of how to use this facility.
 
-          Unless you have a specific reason for disabling this, say Y.
+	  Unless you have a specific reason for disabling this, say Y.
 
 config NULL_CHAN
 	bool "null channel support"
 	help
-          This option enables support for attaching UML consoles and serial
-          lines to a device similar to /dev/null.  Data written to it disappears
-          and there is never any data to be read.
+	  This option enables support for attaching UML consoles and serial
+	  lines to a device similar to /dev/null.  Data written to it disappears
+	  and there is never any data to be read.
 
 config PORT_CHAN
 	bool "port channel support"
 	help
-          This option enables support for attaching UML consoles and serial
-          lines to host portals.  They may be accessed with 'telnet <host>
-          <port number>'.  Any number of consoles and serial lines may be
-          attached to a single portal, although what UML device you get when
-          you telnet to that portal will be unpredictable.
-          It is safe to say 'Y' here.
+	  This option enables support for attaching UML consoles and serial
+	  lines to host portals.  They may be accessed with 'telnet <host>
+	  <port number>'.  Any number of consoles and serial lines may be
+	  attached to a single portal, although what UML device you get when
+	  you telnet to that portal will be unpredictable.
+	  It is safe to say 'Y' here.
 
 config PTY_CHAN
 	bool "pty channel support"
 	help
-          This option enables support for attaching UML consoles and serial
-          lines to host pseudo-terminals.  Access to both traditional
-          pseudo-terminals (/dev/pty*) and pts pseudo-terminals are controlled
-          with this option.  The assignment of UML devices to host devices
-          will be announced in the kernel message log.
-          It is safe to say 'Y' here.
+	  This option enables support for attaching UML consoles and serial
+	  lines to host pseudo-terminals.  Access to both traditional
+	  pseudo-terminals (/dev/pty*) and pts pseudo-terminals are controlled
+	  with this option.  The assignment of UML devices to host devices
+	  will be announced in the kernel message log.
+	  It is safe to say 'Y' here.
 
 config TTY_CHAN
 	bool "tty channel support"
 	help
-          This option enables support for attaching UML consoles and serial
-          lines to host terminals.  Access to both virtual consoles
-          (/dev/tty*) and the slave side of pseudo-terminals (/dev/ttyp* and
-          /dev/pts/*) are controlled by this option.
-          It is safe to say 'Y' here.
+	  This option enables support for attaching UML consoles and serial
+	  lines to host terminals.  Access to both virtual consoles
+	  (/dev/tty*) and the slave side of pseudo-terminals (/dev/ttyp* and
+	  /dev/pts/*) are controlled by this option.
+	  It is safe to say 'Y' here.
 
 config XTERM_CHAN
 	bool "xterm channel support"
 	help
-          This option enables support for attaching UML consoles and serial
-          lines to xterms.  Each UML device so assigned will be brought up in
-          its own xterm.
-          It is safe to say 'Y' here.
+	  This option enables support for attaching UML consoles and serial
+	  lines to xterms.  Each UML device so assigned will be brought up in
+	  its own xterm.
+	  It is safe to say 'Y' here.
 
 config NOCONFIG_CHAN
 	bool
@@ -72,43 +72,43 @@
 	string "Default main console channel initialization"
 	default "fd:0,fd:1"
 	help
-          This is the string describing the channel to which the main console
-          will be attached by default.  This value can be overridden from the
-          command line.  The default value is "fd:0,fd:1", which attaches the
-          main console to stdin and stdout.
-          It is safe to leave this unchanged.
+	  This is the string describing the channel to which the main console
+	  will be attached by default.  This value can be overridden from the
+	  command line.  The default value is "fd:0,fd:1", which attaches the
+	  main console to stdin and stdout.
+	  It is safe to leave this unchanged.
 
 config CON_CHAN
 	string "Default console channel initialization"
 	default "xterm"
 	help
-          This is the string describing the channel to which all consoles
-          except the main console will be attached by default.  This value can
-          be overridden from the command line.  The default value is "xterm",
-          which brings them up in xterms.
-          It is safe to leave this unchanged, although you may wish to change
-          this if you expect the UML that you build to be run in environments
-          which don't have X or xterm available.
+	  This is the string describing the channel to which all consoles
+	  except the main console will be attached by default.  This value can
+	  be overridden from the command line.  The default value is "xterm",
+	  which brings them up in xterms.
+	  It is safe to leave this unchanged, although you may wish to change
+	  this if you expect the UML that you build to be run in environments
+	  which don't have X or xterm available.
 
 config SSL_CHAN
 	string "Default serial line channel initialization"
 	default "pty"
 	help
-          This is the string describing the channel to which the serial lines
-          will be attached by default.  This value can be overridden from the
-          command line.  The default value is "pty", which attaches them to
-          traditional pseudo-terminals.
-          It is safe to leave this unchanged, although you may wish to change
-          this if you expect the UML that you build to be run in environments
-          which don't have a set of /dev/pty* devices.
+	  This is the string describing the channel to which the serial lines
+	  will be attached by default.  This value can be overridden from the
+	  command line.  The default value is "pty", which attaches them to
+	  traditional pseudo-terminals.
+	  It is safe to leave this unchanged, although you may wish to change
+	  this if you expect the UML that you build to be run in environments
+	  which don't have a set of /dev/pty* devices.
 
 config UML_SOUND
 	tristate "Sound support"
 	help
-          This option enables UML sound support.  If enabled, it will pull in
-          soundcore and the UML hostaudio relay, which acts as a intermediary
-          between the host's dsp and mixer devices and the UML sound system.
-          It is safe to say 'Y' here.
+	  This option enables UML sound support.  If enabled, it will pull in
+	  soundcore and the UML hostaudio relay, which acts as a intermediary
+	  between the host's dsp and mixer devices and the UML sound system.
+	  It is safe to say 'Y' here.
 
 config SOUND
 	tristate
@@ -131,107 +131,107 @@
 config UML_NET
 	bool "Virtual network device"
 	help
-        While the User-Mode port cannot directly talk to any physical
-        hardware devices, this choice and the following transport options
-        provide one or more virtual network devices through which the UML
-        kernels can talk to each other, the host, and with the host's help,
-        machines on the outside world.
+	  While the User-Mode port cannot directly talk to any physical
+	  hardware devices, this choice and the following transport options
+	  provide one or more virtual network devices through which the UML
+	  kernels can talk to each other, the host, and with the host's help,
+	  machines on the outside world.
 
-        For more information, including explanations of the networking and
-        sample configurations, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>.
+	  For more information, including explanations of the networking and
+	  sample configurations, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>.
 
-        If you'd like to be able to enable networking in the User-Mode
-        linux environment, say Y; otherwise say N.  Note that you must
-        enable at least one of the following transport options to actually
-        make use of UML networking.
+	  If you'd like to be able to enable networking in the User-Mode
+	  linux environment, say Y; otherwise say N.  Note that you must
+	  enable at least one of the following transport options to actually
+	  make use of UML networking.
 
 config UML_NET_ETHERTAP
 	bool "Ethertap transport"
 	depends on UML_NET
 	help
-        The Ethertap User-Mode Linux network transport allows a single
-        running UML to exchange packets with its host over one of the
-        host's Ethertap devices, such as /dev/tap0.  Additional running
-        UMLs can use additional Ethertap devices, one per running UML.
-        While the UML believes it's on a (multi-device, broadcast) virtual
-        Ethernet network, it's in fact communicating over a point-to-point
-        link with the host.
+	  The Ethertap User-Mode Linux network transport allows a single
+	  running UML to exchange packets with its host over one of the
+	  host's Ethertap devices, such as /dev/tap0.  Additional running
+	  UMLs can use additional Ethertap devices, one per running UML.
+	  While the UML believes it's on a (multi-device, broadcast) virtual
+	  Ethernet network, it's in fact communicating over a point-to-point
+	  link with the host.
 
-        To use this, your host kernel must have support for Ethertap
-        devices.  Also, if your host kernel is 2.4.x, it must have
-        CONFIG_NETLINK_DEV configured as Y or M.
+	  To use this, your host kernel must have support for Ethertap
+	  devices.  Also, if your host kernel is 2.4.x, it must have
+	  CONFIG_NETLINK_DEV configured as Y or M.
 
-        For more information, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
-        has examples of the UML command line to use to enable Ethertap
-        networking.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
+	  has examples of the UML command line to use to enable Ethertap
+	  networking.
 
-        If you'd like to set up an IP network with the host and/or the
-        outside world, say Y to this, the Daemon Transport and/or the
-        Slip Transport.  You'll need at least one of them, but may choose
-        more than one without conflict.  If you don't need UML networking,
-        say N.
+	  If you'd like to set up an IP network with the host and/or the
+	  outside world, say Y to this, the Daemon Transport and/or the
+	  Slip Transport.  You'll need at least one of them, but may choose
+	  more than one without conflict.  If you don't need UML networking,
+	  say N.
 
 config UML_NET_TUNTAP
 	bool "TUN/TAP transport"
 	depends on UML_NET
 	help
-        The UML TUN/TAP network transport allows a UML instance to exchange
-        packets with the host over a TUN/TAP device.  This option will only
-        work with a 2.4 host, unless you've applied the TUN/TAP patch to
-        your 2.2 host kernel.
+	  The UML TUN/TAP network transport allows a UML instance to exchange
+	  packets with the host over a TUN/TAP device.  This option will only
+	  work with a 2.4 host, unless you've applied the TUN/TAP patch to
+	  your 2.2 host kernel.
 
-        To use this transport, your host kernel must have support for TUN/TAP
-        devices, either built-in or as a module.
+	  To use this transport, your host kernel must have support for TUN/TAP
+	  devices, either built-in or as a module.
 
 config UML_NET_SLIP
 	bool "SLIP transport"
 	depends on UML_NET
 	help
-        The slip User-Mode Linux network transport allows a running UML to
-        network with its host over a point-to-point link.  Unlike Ethertap,
-        which can carry any Ethernet frame (and hence even non-IP packets),
-        the slip transport can only carry IP packets.
+	  The slip User-Mode Linux network transport allows a running UML to
+	  network with its host over a point-to-point link.  Unlike Ethertap,
+	  which can carry any Ethernet frame (and hence even non-IP packets),
+	  the slip transport can only carry IP packets.
 
-        To use this, your host must support slip devices.
+	  To use this, your host must support slip devices.
 
-        For more information, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>.
-        has examples of the UML command line to use to enable slip
-        networking, and details of a few quirks with it.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>.
+	  has examples of the UML command line to use to enable slip
+	  networking, and details of a few quirks with it.
 
-        The Ethertap Transport is preferred over slip because of its
-        limitations.  If you prefer slip, however, say Y here.  Otherwise
-        choose the Multicast transport (to network multiple UMLs on
-        multiple hosts), Ethertap (to network with the host and the
-        outside world), and/or the Daemon transport (to network multiple
-        UMLs on a single host).  You may choose more than one without
-        conflict.  If you don't need UML networking, say N.
+	  The Ethertap Transport is preferred over slip because of its
+	  limitations.  If you prefer slip, however, say Y here.  Otherwise
+	  choose the Multicast transport (to network multiple UMLs on
+	  multiple hosts), Ethertap (to network with the host and the
+	  outside world), and/or the Daemon transport (to network multiple
+	  UMLs on a single host).  You may choose more than one without
+	  conflict.  If you don't need UML networking, say N.
 
 config UML_NET_DAEMON
 	bool "Daemon transport"
 	depends on UML_NET
 	help
-        This User-Mode Linux network transport allows one or more running
-        UMLs on a single host to communicate with each other, but not to
-        the host.
+	  This User-Mode Linux network transport allows one or more running
+	  UMLs on a single host to communicate with each other, but not to
+	  the host.
 
-        To use this form of networking, you'll need to run the UML
-        networking daemon on the host.
+	  To use this form of networking, you'll need to run the UML
+	  networking daemon on the host.
 
-        For more information, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
-        has examples of the UML command line to use to enable Daemon
-        networking.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
+	  has examples of the UML command line to use to enable Daemon
+	  networking.
 
-        If you'd like to set up a network with other UMLs on a single host,
-        say Y.  If you need a network between UMLs on multiple physical
-        hosts, choose the Multicast Transport.  To set up a network with
-        the host and/or other IP machines, say Y to the Ethertap or Slip
-        transports.  You'll need at least one of them, but may choose
-        more than one without conflict.  If you don't need UML networking,
-        say N.
+	  If you'd like to set up a network with other UMLs on a single host,
+	  say Y.  If you need a network between UMLs on multiple physical
+	  hosts, choose the Multicast Transport.  To set up a network with
+	  the host and/or other IP machines, say Y to the Ethertap or Slip
+	  transports.  You'll need at least one of them, but may choose
+	  more than one without conflict.  If you don't need UML networking,
+	  say N.
 
 config UML_NET_VECTOR
 	bool "Vector I/O high performance network devices"
@@ -270,26 +270,26 @@
 	bool "Multicast transport"
 	depends on UML_NET
 	help
-        This Multicast User-Mode Linux network transport allows multiple
-        UMLs (even ones running on different host machines!) to talk to
-        each other over a virtual ethernet network.  However, it requires
-        at least one UML with one of the other transports to act as a
-        bridge if any of them need to be able to talk to their hosts or any
-        other IP machines.
+	  This Multicast User-Mode Linux network transport allows multiple
+	  UMLs (even ones running on different host machines!) to talk to
+	  each other over a virtual ethernet network.  However, it requires
+	  at least one UML with one of the other transports to act as a
+	  bridge if any of them need to be able to talk to their hosts or any
+	  other IP machines.
 
-        To use this, your host kernel(s) must support IP Multicasting.
+	  To use this, your host kernel(s) must support IP Multicasting.
 
-        For more information, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
-        has examples of the UML command line to use to enable Multicast
-        networking, and notes about the security of this approach.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
+	  has examples of the UML command line to use to enable Multicast
+	  networking, and notes about the security of this approach.
 
-        If you need UMLs on multiple physical hosts to communicate as if
-        they shared an Ethernet network, say Y.  If you need to communicate
-        with other IP machines, make sure you select one of the other
-        transports (possibly in addition to Multicast; they're not
-        exclusive).  If you don't need to network UMLs say N to each of
-        the transports.
+	  If you need UMLs on multiple physical hosts to communicate as if
+	  they shared an Ethernet network, say Y.  If you need to communicate
+	  with other IP machines, make sure you select one of the other
+	  transports (possibly in addition to Multicast; they're not
+	  exclusive).  If you don't need to network UMLs say N to each of
+	  the transports.
 
 config UML_NET_PCAP
 	bool "pcap transport"
@@ -300,9 +300,9 @@
 	UML act as a network monitor for the host.  You must have libcap
 	installed in order to build the pcap transport into UML.
 
-        For more information, see
-        <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
-        has examples of the UML command line to use to enable this option.
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/old/networking.html>  That site
+	  has examples of the UML command line to use to enable this option.
 
 	If you intend to use UML as a network monitor for the host, say
 	Y here.  Otherwise, say N.
@@ -311,27 +311,34 @@
 	bool "SLiRP transport"
 	depends on UML_NET
 	help
-        The SLiRP User-Mode Linux network transport allows a running UML
-        to network by invoking a program that can handle SLIP encapsulated
-        packets.  This is commonly (but not limited to) the application
-        known as SLiRP, a program that can re-socket IP packets back onto
-        the host on which it is run.  Only IP packets are supported,
-        unlike other network transports that can handle all Ethernet
-        frames.  In general, slirp allows the UML the same IP connectivity
-        to the outside world that the host user is permitted, and unlike
-        other transports, SLiRP works without the need of root level
-        privleges, setuid binaries, or SLIP devices on the host.  This
-        also means not every type of connection is possible, but most
-        situations can be accommodated with carefully crafted slirp
-        commands that can be passed along as part of the network device's
-        setup string.  The effect of this transport on the UML is similar
-        that of a host behind a firewall that masquerades all network
-        connections passing through it (but is less secure).
+	  The SLiRP User-Mode Linux network transport allows a running UML
+	  to network by invoking a program that can handle SLIP encapsulated
+	  packets.  This is commonly (but not limited to) the application
+	  known as SLiRP, a program that can re-socket IP packets back onto
+	  he host on which it is run.  Only IP packets are supported,
+	  unlike other network transports that can handle all Ethernet
+	  frames.  In general, slirp allows the UML the same IP connectivity
+	  to the outside world that the host user is permitted, and unlike
+	  other transports, SLiRP works without the need of root level
+	  privleges, setuid binaries, or SLIP devices on the host.  This
+	  also means not every type of connection is possible, but most
+	  situations can be accommodated with carefully crafted slirp
+	  commands that can be passed along as part of the network device's
+	  setup string.  The effect of this transport on the UML is similar
+	  that of a host behind a firewall that masquerades all network
+	  connections passing through it (but is less secure).
 
-        To use this you should first have slirp compiled somewhere
-        accessible on the host, and have read its documentation.  If you
-        don't need UML networking, say N.
+	  To use this you should first have slirp compiled somewhere
+	  accessible on the host, and have read its documentation.  If you
+	  don't need UML networking, say N.
 
-        Startup example: "eth0=slirp,FE:FD:01:02:03:04,/usr/local/bin/slirp"
+	  Startup example: "eth0=slirp,FE:FD:01:02:03:04,/usr/local/bin/slirp"
 
 endmenu
+
+config VIRTIO_UML
+	tristate "UML driver for virtio devices"
+	select VIRTIO
+	help
+	  This driver provides support for virtio based paravirtual device
+	  drivers over vhost-user sockets.
diff --git a/arch/um/drivers/Makefile b/arch/um/drivers/Makefile
index 6933198..a290821 100644
--- a/arch/um/drivers/Makefile
+++ b/arch/um/drivers/Makefile
@@ -1,6 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
 # 
 # Copyright (C) 2000, 2002, 2003 Jeff Dike (jdike@karaya.com)
-# Licensed under the GPL
 #
 
 # pcap is broken in 2.5 because kbuild doesn't allow pcap.a to be linked
@@ -61,6 +61,7 @@
 obj-$(CONFIG_UML_WATCHDOG) += harddog.o
 obj-$(CONFIG_BLK_DEV_COW_COMMON) += cow_user.o
 obj-$(CONFIG_UML_RANDOM) += random.o
+obj-$(CONFIG_VIRTIO_UML) += virtio_uml.o
 
 # pcap_user.o must be added explicitly.
 USER_OBJS := fd.o null.o pty.o tty.o xterm.o slip_common.o pcap_user.o vde_user.o vector_user.o
diff --git a/arch/um/drivers/chan.h b/arch/um/drivers/chan.h
index c512b03..c37cc4f 100644
--- a/arch/um/drivers/chan.h
+++ b/arch/um/drivers/chan.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __CHAN_KERN_H__
diff --git a/arch/um/drivers/chan_kern.c b/arch/um/drivers/chan_kern.c
index 05588f9..6299705 100644
--- a/arch/um/drivers/chan_kern.c
+++ b/arch/um/drivers/chan_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <linux/slab.h>
@@ -171,19 +171,55 @@
 	return err;
 }
 
+/* Items are added in IRQ context, when free_irq can't be called, and
+ * removed in process context, when it can.
+ * This handles interrupt sources which disappear, and which need to
+ * be permanently disabled.  This is discovered in IRQ context, but
+ * the freeing of the IRQ must be done later.
+ */
+static DEFINE_SPINLOCK(irqs_to_free_lock);
+static LIST_HEAD(irqs_to_free);
+
+void free_irqs(void)
+{
+	struct chan *chan;
+	LIST_HEAD(list);
+	struct list_head *ele;
+	unsigned long flags;
+
+	spin_lock_irqsave(&irqs_to_free_lock, flags);
+	list_splice_init(&irqs_to_free, &list);
+	spin_unlock_irqrestore(&irqs_to_free_lock, flags);
+
+	list_for_each(ele, &list) {
+		chan = list_entry(ele, struct chan, free_list);
+
+		if (chan->input && chan->enabled)
+			um_free_irq(chan->line->driver->read_irq, chan);
+		if (chan->output && chan->enabled)
+			um_free_irq(chan->line->driver->write_irq, chan);
+		chan->enabled = 0;
+	}
+}
+
 static void close_one_chan(struct chan *chan, int delay_free_irq)
 {
+	unsigned long flags;
+
 	if (!chan->opened)
 		return;
 
-    /* we can safely call free now - it will be marked
-     *  as free and freed once the IRQ stopped processing
-     */
-	if (chan->input && chan->enabled)
-		um_free_irq(chan->line->driver->read_irq, chan);
-	if (chan->output && chan->enabled)
-		um_free_irq(chan->line->driver->write_irq, chan);
-	chan->enabled = 0;
+	if (delay_free_irq) {
+		spin_lock_irqsave(&irqs_to_free_lock, flags);
+		list_add(&chan->free_list, &irqs_to_free);
+		spin_unlock_irqrestore(&irqs_to_free_lock, flags);
+	} else {
+		if (chan->input && chan->enabled)
+			um_free_irq(chan->line->driver->read_irq, chan);
+		if (chan->output && chan->enabled)
+			um_free_irq(chan->line->driver->write_irq, chan);
+		chan->enabled = 0;
+	}
 	if (chan->ops->close != NULL)
 		(*chan->ops->close)(chan->fd, chan->data);
 
@@ -211,12 +247,6 @@
 		deactivate_fd(chan->fd, irq);
 }
 
-void reactivate_chan(struct chan *chan, int irq)
-{
-	if (chan && chan->enabled)
-		reactivate_fd(chan->fd, irq);
-}
-
 int write_chan(struct chan *chan, const char *buf, int len,
 	       int write_irq)
 {
@@ -228,8 +258,6 @@
 	n = chan->ops->write(chan->fd, buf, len, chan->data);
 	if (chan->primary) {
 		ret = n;
-		if ((ret == -EAGAIN) || ((ret >= 0) && (ret < len)))
-			reactivate_fd(chan->fd, write_irq);
 	}
 	return ret;
 }
@@ -527,8 +555,6 @@
 			tty_insert_flip_char(port, c, TTY_NORMAL);
 	} while (err > 0);
 
-	if (err == 0)
-		reactivate_fd(chan->fd, irq);
 	if (err == -EIO) {
 		if (chan->primary) {
 			tty_port_tty_hangup(&line->port, false);
diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
index 3fd7c3e..4d80526 100644
--- a/arch/um/drivers/chan_user.c
+++ b/arch/um/drivers/chan_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
diff --git a/arch/um/drivers/chan_user.h b/arch/um/drivers/chan_user.h
index 03f1b56..72222bb 100644
--- a/arch/um/drivers/chan_user.h
+++ b/arch/um/drivers/chan_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __CHAN_USER_H__
diff --git a/arch/um/drivers/cow_user.c b/arch/um/drivers/cow_user.c
index 0ee9cc6..74b0c26 100644
--- a/arch/um/drivers/cow_user.c
+++ b/arch/um/drivers/cow_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 /*
diff --git a/arch/um/drivers/daemon.h b/arch/um/drivers/daemon.h
index c2dd195..1509cc7 100644
--- a/arch/um/drivers/daemon.h
+++ b/arch/um/drivers/daemon.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __DAEMON_H__
diff --git a/arch/um/drivers/daemon_kern.c b/arch/um/drivers/daemon_kern.c
index 7568cc2..fd24026 100644
--- a/arch/um/drivers/daemon_kern.c
+++ b/arch/um/drivers/daemon_kern.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
 #include <linux/init.h>
diff --git a/arch/um/drivers/daemon_user.c b/arch/um/drivers/daemon_user.c
index 8813c10..3695821 100644
--- a/arch/um/drivers/daemon_user.c
+++ b/arch/um/drivers/daemon_user.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
 #include <stdint.h>
diff --git a/arch/um/drivers/fd.c b/arch/um/drivers/fd.c
index a13a427..082d739 100644
--- a/arch/um/drivers/fd.c
+++ b/arch/um/drivers/fd.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/drivers/harddog_kern.c b/arch/um/drivers/harddog_kern.c
index 6d38127..000cb69 100644
--- a/arch/um/drivers/harddog_kern.c
+++ b/arch/um/drivers/harddog_kern.c
@@ -85,7 +85,7 @@
 	timer_alive = 1;
 	spin_unlock(&lock);
 	mutex_unlock(&harddog_mutex);
-	return nonseekable_open(inode, file);
+	return stream_open(inode, file);
 err:
 	spin_unlock(&lock);
 	mutex_unlock(&harddog_mutex);
diff --git a/arch/um/drivers/harddog_user.c b/arch/um/drivers/harddog_user.c
index 3aa8b0d..070468d 100644
--- a/arch/um/drivers/harddog_user.c
+++ b/arch/um/drivers/harddog_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/drivers/hostaudio_kern.c b/arch/um/drivers/hostaudio_kern.c
index 7f9dbdb..bf75b1c 100644
--- a/arch/um/drivers/hostaudio_kern.c
+++ b/arch/um/drivers/hostaudio_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 Steve Schmidtke
- * Licensed under the GPL
  */
 
 #include <linux/fs.h>
diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
index 8d80b27..4f2a4ac 100644
--- a/arch/um/drivers/line.c
+++ b/arch/um/drivers/line.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/irqreturn.h>
@@ -235,14 +235,6 @@
 
 	line->throttled = 0;
 	chan_interrupt(line, line->driver->read_irq);
-
-	/*
-	 * Maybe there is enough stuff pending that calling the interrupt
-	 * throttles us again.  In this case, line->throttled will be 1
-	 * again and we shouldn't turn the interrupt back on.
-	 */
-	if (!line->throttled)
-		reactivate_chan(line->chan_in, line->driver->read_irq);
 }
 
 static irqreturn_t line_write_interrupt(int irq, void *data)
@@ -261,7 +253,7 @@
 	if (err == 0) {
 		spin_unlock(&line->lock);
 		return IRQ_NONE;
-	} else if (err < 0) {
+	} else if ((err < 0) && (err != -EAGAIN)) {
 		line->head = line->buffer;
 		line->tail = line->buffer;
 	}
@@ -284,7 +276,7 @@
 	if (err)
 		return err;
 	if (output)
-		err = um_request_irq(driver->write_irq, fd, IRQ_NONE,
+		err = um_request_irq(driver->write_irq, fd, IRQ_WRITE,
 				     line_write_interrupt, IRQF_SHARED,
 				     driver->write_irq_name, data);
 	return err;
@@ -667,8 +659,6 @@
 		tty_kref_put(tty);
 	}
  out:
-	if (winch->fd != -1)
-		reactivate_fd(winch->fd, WINCH_IRQ);
 	return IRQ_HANDLED;
 }
 
diff --git a/arch/um/drivers/line.h b/arch/um/drivers/line.h
index 138a145..a151ff5 100644
--- a/arch/um/drivers/line.h
+++ b/arch/um/drivers/line.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __LINE_H__
diff --git a/arch/um/drivers/mconsole.h b/arch/um/drivers/mconsole.h
index 44af737..6356378 100644
--- a/arch/um/drivers/mconsole.h
+++ b/arch/um/drivers/mconsole.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __MCONSOLE_H__
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index d5f9a2d..0117489 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
  * Copyright (C) 2001 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/console.h>
@@ -96,7 +96,6 @@
 	}
 	if (!list_empty(&mc_requests))
 		schedule_work(&mconsole_work);
-	reactivate_fd(fd, MCONSOLE_IRQ);
 	return IRQ_HANDLED;
 }
 
@@ -240,7 +239,6 @@
 		(*req->cmd->handler)(req);
 	}
 	os_set_fd_block(req->originating_fd, 0);
-	reactivate_fd(req->originating_fd, MCONSOLE_IRQ);
 	mconsole_reply(req, "", 0, 0);
 }
 
diff --git a/arch/um/drivers/mconsole_kern.h b/arch/um/drivers/mconsole_kern.h
index 7a0c6a1..56d8d6a 100644
--- a/arch/um/drivers/mconsole_kern.h
+++ b/arch/um/drivers/mconsole_kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __MCONSOLE_KERN_H__
diff --git a/arch/um/drivers/mconsole_user.c b/arch/um/drivers/mconsole_user.c
index 9920982..e24298a 100644
--- a/arch/um/drivers/mconsole_user.c
+++ b/arch/um/drivers/mconsole_user.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <errno.h>
diff --git a/arch/um/drivers/mmapper_kern.c b/arch/um/drivers/mmapper_kern.c
index 3645fcb..0bf78ff 100644
--- a/arch/um/drivers/mmapper_kern.c
+++ b/arch/um/drivers/mmapper_kern.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * arch/um/drivers/mmapper_kern.c
  *
diff --git a/arch/um/drivers/net_kern.c b/arch/um/drivers/net_kern.c
index 3ef1b48..327b728 100644
--- a/arch/um/drivers/net_kern.c
+++ b/arch/um/drivers/net_kern.c
@@ -1,12 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
-#include <linux/bootmem.h>
+#include <linux/memblock.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
 #include <linux/inetdevice.h>
@@ -137,8 +137,6 @@
 		schedule_work(&lp->work);
 		goto out;
 	}
-	reactivate_fd(lp->fd, UM_ETH_IRQ);
-
 out:
 	spin_unlock(&lp->lock);
 	return IRQ_HANDLED;
@@ -650,7 +648,10 @@
 		return 1;
 	}
 
-	new = alloc_bootmem(sizeof(*new));
+	new = memblock_alloc(sizeof(*new), SMP_CACHE_BYTES);
+	if (!new)
+		panic("%s: Failed to allocate %zu bytes\n", __func__,
+		      sizeof(*new));
 
 	INIT_LIST_HEAD(&new->list);
 	new->index = n;
diff --git a/arch/um/drivers/net_user.c b/arch/um/drivers/net_user.c
index e9f8445..4c95764 100644
--- a/arch/um/drivers/net_user.c
+++ b/arch/um/drivers/net_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/drivers/null.c b/arch/um/drivers/null.c
index 1049574..8708776 100644
--- a/arch/um/drivers/null.c
+++ b/arch/um/drivers/null.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <stddef.h>
diff --git a/arch/um/drivers/pcap_kern.c b/arch/um/drivers/pcap_kern.c
index be0fb57..cfe4cb1 100644
--- a/arch/um/drivers/pcap_kern.c
+++ b/arch/um/drivers/pcap_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <linux/init.h>
diff --git a/arch/um/drivers/pcap_user.c b/arch/um/drivers/pcap_user.c
index c07b9c7..bbd2063 100644
--- a/arch/um/drivers/pcap_user.c
+++ b/arch/um/drivers/pcap_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <errno.h>
diff --git a/arch/um/drivers/pcap_user.h b/arch/um/drivers/pcap_user.h
index 1ca7c76..216246f 100644
--- a/arch/um/drivers/pcap_user.h
+++ b/arch/um/drivers/pcap_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <net_user.h>
diff --git a/arch/um/drivers/port.h b/arch/um/drivers/port.h
index 372a80c..9085b33 100644
--- a/arch/um/drivers/port.h
+++ b/arch/um/drivers/port.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __PORT_H__
diff --git a/arch/um/drivers/port_kern.c b/arch/um/drivers/port_kern.c
index 40ca5cc..a47ca53 100644
--- a/arch/um/drivers/port_kern.c
+++ b/arch/um/drivers/port_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <linux/completion.h>
@@ -137,7 +137,6 @@
 		if (!port->has_connection)
 			continue;
 
-		reactivate_fd(port->fd, ACCEPT_IRQ);
 		while (port_accept(port))
 			;
 		port->has_connection = 0;
diff --git a/arch/um/drivers/port_user.c b/arch/um/drivers/port_user.c
index 9a8e1b6..5b5b64c 100644
--- a/arch/um/drivers/port_user.c
+++ b/arch/um/drivers/port_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
@@ -168,7 +168,7 @@
 {
 	int new, err;
 	char *argv[] = { "/usr/sbin/in.telnetd", "-L",
-			 "/usr/lib/uml/port-helper", NULL };
+			 OS_LIB_PATH "/uml/port-helper", NULL };
 	struct port_pre_exec_data data;
 
 	new = accept(fd, NULL, 0);
diff --git a/arch/um/drivers/pty.c b/arch/um/drivers/pty.c
index f1fcc2c..39c6006 100644
--- a/arch/um/drivers/pty.c
+++ b/arch/um/drivers/pty.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/drivers/random.c b/arch/um/drivers/random.c
index 778a0e5..1d5d305 100644
--- a/arch/um/drivers/random.c
+++ b/arch/um/drivers/random.c
@@ -73,7 +73,6 @@
 				return ret ? : -EAGAIN;
 
 			atomic_inc(&host_sleep_count);
-			reactivate_fd(random_fd, RANDOM_IRQ);
 			add_sigio_fd(random_fd);
 
 			add_wait_queue(&host_read_wait, &wait);
diff --git a/arch/um/drivers/slip_kern.c b/arch/um/drivers/slip_kern.c
index ed5249f..c58ccdc 100644
--- a/arch/um/drivers/slip_kern.c
+++ b/arch/um/drivers/slip_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <linux/if_arp.h>
diff --git a/arch/um/drivers/slip_user.c b/arch/um/drivers/slip_user.c
index 0d6b66c..8016d32 100644
--- a/arch/um/drivers/slip_user.c
+++ b/arch/um/drivers/slip_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <stdio.h>
diff --git a/arch/um/drivers/slirp_kern.c b/arch/um/drivers/slirp_kern.c
index 4ef11ca..2d97692 100644
--- a/arch/um/drivers/slirp_kern.c
+++ b/arch/um/drivers/slirp_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <linux/if_arp.h>
diff --git a/arch/um/drivers/slirp_user.c b/arch/um/drivers/slirp_user.c
index 98b6a41..8f633e2 100644
--- a/arch/um/drivers/slirp_user.c
+++ b/arch/um/drivers/slirp_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL.
  */
 
 #include <unistd.h>
diff --git a/arch/um/drivers/ssl.c b/arch/um/drivers/ssl.c
index b8d14fa..b213201 100644
--- a/arch/um/drivers/ssl.c
+++ b/arch/um/drivers/ssl.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2000, 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <linux/fs.h>
@@ -12,7 +12,6 @@
 #include <linux/console.h>
 #include <asm/termbits.h>
 #include <asm/irq.h>
-#include "ssl.h"
 #include "chan.h"
 #include <init.h>
 #include <irq_user.h>
diff --git a/arch/um/drivers/ssl.h b/arch/um/drivers/ssl.h
deleted file mode 100644
index 314d177..0000000
--- a/arch/um/drivers/ssl.h
+++ /dev/null
@@ -1,13 +0,0 @@
-/* 
- * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
- */
-
-#ifndef __SSL_H__
-#define __SSL_H__
-
-extern int ssl_read(int fd, int line);
-extern void ssl_receive_char(int line, char ch);
-
-#endif
-
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
index c90817b..0021d7f 100644
--- a/arch/um/drivers/stdio_console.c
+++ b/arch/um/drivers/stdio_console.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <linux/posix_types.h>
diff --git a/arch/um/drivers/stdio_console.h b/arch/um/drivers/stdio_console.h
index 6d8275f..3a409ec 100644
--- a/arch/um/drivers/stdio_console.h
+++ b/arch/um/drivers/stdio_console.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __STDIO_CONSOLE_H
diff --git a/arch/um/drivers/tty.c b/arch/um/drivers/tty.c
index eaa201b..884a762 100644
--- a/arch/um/drivers/tty.c
+++ b/arch/um/drivers/tty.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <errno.h>
diff --git a/arch/um/drivers/ubd.h b/arch/um/drivers/ubd.h
index cc1cc85..f016fe1 100644
--- a/arch/um/drivers/ubd.h
+++ b/arch/um/drivers/ubd.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
  * Copyright (C) 2001 RidgeRun, Inc (glonnon@ridgerun.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_UBD_USER_H
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 83c4703..6627d7c 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1,7 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
+ * Copyright (C) 2018 Cambridge Greys Ltd
  * Copyright (C) 2015-2016 Anton Ivanov (aivanov@brocade.com)
  * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 /* 2001-09-28...2002-04-17
@@ -23,6 +24,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/blkdev.h>
+#include <linux/blk-mq.h>
 #include <linux/ata.h>
 #include <linux/hdreg.h>
 #include <linux/cdrom.h>
@@ -42,11 +44,11 @@
 #include <os.h>
 #include "cow.h"
 
-enum ubd_req { UBD_READ, UBD_WRITE, UBD_FLUSH };
+/* Max request size is determined by sector mask - 32K */
+#define UBD_MAX_REQUEST (8 * sizeof(long))
 
 struct io_thread_req {
 	struct request *req;
-	enum ubd_req op;
 	int fds[2];
 	unsigned long offsets[2];
 	unsigned long long offset;
@@ -142,7 +144,6 @@
 #define MAX_SG 64
 
 struct ubd {
-	struct list_head restart;
 	/* name (and fd, below) of the file opened for writing, either the
 	 * backing or the cow file. */
 	char *file;
@@ -153,14 +154,12 @@
 	struct openflags openflags;
 	unsigned shared:1;
 	unsigned no_cow:1;
+	unsigned no_trim:1;
 	struct cow cow;
 	struct platform_device pdev;
 	struct request_queue *queue;
+	struct blk_mq_tag_set tag_set;
 	spinlock_t lock;
-	struct scatterlist sg[MAX_SG];
-	struct request *request;
-	int start_sg, end_sg;
-	sector_t rq_pos;
 };
 
 #define DEFAULT_COW { \
@@ -179,13 +178,10 @@
 	.boot_openflags =	OPEN_FLAGS, \
 	.openflags =		OPEN_FLAGS, \
 	.no_cow =               0, \
+	.no_trim =		0, \
 	.shared =		0, \
 	.cow =			DEFAULT_COW, \
 	.lock =			__SPIN_LOCK_UNLOCKED(ubd_devs.lock), \
-	.request =		NULL, \
-	.start_sg =		0, \
-	.end_sg =		0, \
-	.rq_pos =		0, \
 }
 
 /* Protected by ubd_lock */
@@ -196,6 +192,9 @@
 static struct proc_dir_entry *proc_ide_root = NULL;
 static struct proc_dir_entry *proc_ide = NULL;
 
+static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				 const struct blk_mq_queue_data *bd);
+
 static void make_proc_ide(void)
 {
 	proc_ide_root = proc_mkdir("ide", NULL);
@@ -277,14 +276,14 @@
 		str++;
 		if(!strcmp(str, "sync")){
 			global_openflags = of_sync(global_openflags);
-			goto out1;
+			return err;
 		}
 
 		err = -EINVAL;
 		major = simple_strtoul(str, &end, 0);
 		if((*end != '\0') || (end == str)){
 			*error_out = "Didn't parse major number";
-			goto out1;
+			return err;
 		}
 
 		mutex_lock(&ubd_lock);
@@ -326,7 +325,7 @@
 		*index_out = n;
 
 	err = -EINVAL;
-	for (i = 0; i < sizeof("rscd="); i++) {
+	for (i = 0; i < sizeof("rscdt="); i++) {
 		switch (*str) {
 		case 'r':
 			flags.w = 0;
@@ -340,12 +339,15 @@
 		case 'c':
 			ubd_dev->shared = 1;
 			break;
+		case 't':
+			ubd_dev->no_trim = 1;
+			break;
 		case '=':
 			str++;
 			goto break_loop;
 		default:
 			*error_out = "Expected '=' or flag letter "
-				"(r, s, c, or d)";
+				"(r, s, c, t or d)";
 			goto out;
 		}
 		str++;
@@ -418,6 +420,7 @@
 "    'c' will cause the device to be treated as being shared between multiple\n"
 "    UMLs and file locking will be turned off - this is appropriate for a\n"
 "    cluster filesystem and inappropriate at almost all other times.\n\n"
+"    't' will disable trim/discard support on the device (enabled by default).\n\n"
 );
 
 static int udb_setup(char *str)
@@ -436,11 +439,8 @@
 "    in the boot output.\n\n"
 );
 
-static void do_ubd_request(struct request_queue * q);
-
 /* Only changed by ubd_init, which is an initcall. */
 static int thread_fd = -1;
-static LIST_HEAD(restart);
 
 /* Function to read several request pointers at a time
 * handling fractional reads if (and as) needed
@@ -498,9 +498,6 @@
 /* Called without dev->lock held, and only in interrupt context. */
 static void ubd_handler(void)
 {
-	struct ubd *ubd;
-	struct list_head *list, *next_ele;
-	unsigned long flags;
 	int n;
 	int count;
 
@@ -520,22 +517,21 @@
 			return;
 		}
 		for (count = 0; count < n/sizeof(struct io_thread_req *); count++) {
-			blk_end_request(
-				(*irq_req_buffer)[count]->req,
-				BLK_STS_OK,
-				(*irq_req_buffer)[count]->length
-			);
-			kfree((*irq_req_buffer)[count]);
-		}
-	}
-	reactivate_fd(thread_fd, UBD_IRQ);
+			struct io_thread_req *io_req = (*irq_req_buffer)[count];
 
-	list_for_each_safe(list, next_ele, &restart){
-		ubd = container_of(list, struct ubd, restart);
-		list_del_init(&ubd->restart);
-		spin_lock_irqsave(&ubd->lock, flags);
-		do_ubd_request(ubd->queue);
-		spin_unlock_irqrestore(&ubd->lock, flags);
+			if ((io_req->error == BLK_STS_NOTSUPP) && (req_op(io_req->req) == REQ_OP_DISCARD)) {
+				blk_queue_max_discard_sectors(io_req->req->q, 0);
+				blk_queue_max_write_zeroes_sectors(io_req->req->q, 0);
+				blk_queue_flag_clear(QUEUE_FLAG_DISCARD, io_req->req->q);
+			}
+			if ((io_req->error) || (io_req->buffer == NULL))
+				blk_mq_end_request(io_req->req, io_req->error);
+			else {
+				if (!blk_update_request(io_req->req, io_req->error, io_req->length))
+					__blk_mq_end_request(io_req->req, io_req->error);
+			}
+			kfree(io_req);
+		}
 	}
 }
 
@@ -805,7 +801,7 @@
 
 	if((fd == -ENOENT) && create_cow){
 		fd = create_cow_file(ubd_dev->file, ubd_dev->cow.file,
-					  ubd_dev->openflags, 1 << 9, PAGE_SIZE,
+					  ubd_dev->openflags, SECTOR_SIZE, PAGE_SIZE,
 					  &ubd_dev->cow.bitmap_offset,
 					  &ubd_dev->cow.bitmap_len,
 					  &ubd_dev->cow.data_offset);
@@ -846,6 +842,14 @@
 		if(err < 0) goto error;
 		ubd_dev->cow.fd = err;
 	}
+	if (ubd_dev->no_trim == 0) {
+		ubd_dev->queue->limits.discard_granularity = SECTOR_SIZE;
+		ubd_dev->queue->limits.discard_alignment = SECTOR_SIZE;
+		blk_queue_max_discard_sectors(ubd_dev->queue, UBD_MAX_REQUEST);
+		blk_queue_max_write_zeroes_sectors(ubd_dev->queue, UBD_MAX_REQUEST);
+		blk_queue_flag_set(QUEUE_FLAG_DISCARD, ubd_dev->queue);
+	}
+	blk_queue_flag_set(QUEUE_FLAG_NONROT, ubd_dev->queue);
 	return 0;
  error:
 	os_close_file(ubd_dev->fd);
@@ -857,6 +861,7 @@
 	struct ubd *ubd_dev = dev_get_drvdata(dev);
 
 	blk_cleanup_queue(ubd_dev->queue);
+	blk_mq_free_tag_set(&ubd_dev->tag_set);
 	*ubd_dev = ((struct ubd) DEFAULT_UBD);
 }
 
@@ -891,13 +896,17 @@
 
 	disk->private_data = &ubd_devs[unit];
 	disk->queue = ubd_devs[unit].queue;
-	device_add_disk(parent, disk);
+	device_add_disk(parent, disk, NULL);
 
 	*disk_out = disk;
 	return 0;
 }
 
-#define ROUND_BLOCK(n) ((n + ((1 << 9) - 1)) & (-1 << 9))
+#define ROUND_BLOCK(n) ((n + (SECTOR_SIZE - 1)) & (-SECTOR_SIZE))
+
+static const struct blk_mq_ops ubd_mq_ops = {
+	.queue_rq = ubd_queue_rq,
+};
 
 static int ubd_add(int n, char **error_out)
 {
@@ -915,15 +924,23 @@
 
 	ubd_dev->size = ROUND_BLOCK(ubd_dev->size);
 
-	INIT_LIST_HEAD(&ubd_dev->restart);
-	sg_init_table(ubd_dev->sg, MAX_SG);
+	ubd_dev->tag_set.ops = &ubd_mq_ops;
+	ubd_dev->tag_set.queue_depth = 64;
+	ubd_dev->tag_set.numa_node = NUMA_NO_NODE;
+	ubd_dev->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+	ubd_dev->tag_set.driver_data = ubd_dev;
+	ubd_dev->tag_set.nr_hw_queues = 1;
 
-	err = -ENOMEM;
-	ubd_dev->queue = blk_init_queue(do_ubd_request, &ubd_dev->lock);
-	if (ubd_dev->queue == NULL) {
-		*error_out = "Failed to initialize device queue";
+	err = blk_mq_alloc_tag_set(&ubd_dev->tag_set);
+	if (err)
 		goto out;
+
+	ubd_dev->queue = blk_mq_init_queue(&ubd_dev->tag_set);
+	if (IS_ERR(ubd_dev->queue)) {
+		err = PTR_ERR(ubd_dev->queue);
+		goto out_cleanup_tags;
 	}
+
 	ubd_dev->queue->queuedata = ubd_dev;
 	blk_queue_write_cache(ubd_dev->queue, true, false);
 
@@ -931,7 +948,7 @@
 	err = ubd_disk_register(UBD_MAJOR, ubd_dev->size, n, &ubd_gendisk[n]);
 	if(err){
 		*error_out = "Failed to register device";
-		goto out_cleanup;
+		goto out_cleanup_tags;
 	}
 
 	if (fake_major != UBD_MAJOR)
@@ -949,8 +966,10 @@
 out:
 	return err;
 
-out_cleanup:
-	blk_cleanup_queue(ubd_dev->queue);
+out_cleanup_tags:
+	blk_mq_free_tag_set(&ubd_dev->tag_set);
+	if (!(IS_ERR(ubd_dev->queue)))
+		blk_cleanup_queue(ubd_dev->queue);
 	goto out;
 }
 
@@ -1235,10 +1254,10 @@
 			  __u64 bitmap_offset, unsigned long *bitmap_words,
 			  __u64 bitmap_len)
 {
-	__u64 sector = io_offset >> 9;
+	__u64 sector = io_offset >> SECTOR_SHIFT;
 	int i, update_bitmap = 0;
 
-	for(i = 0; i < length >> 9; i++){
+	for (i = 0; i < length >> SECTOR_SHIFT; i++) {
 		if(cow_mask != NULL)
 			ubd_set_bit(i, (unsigned char *) cow_mask);
 		if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
@@ -1272,14 +1291,14 @@
 static void cowify_req(struct io_thread_req *req, unsigned long *bitmap,
 		       __u64 bitmap_offset, __u64 bitmap_len)
 {
-	__u64 sector = req->offset >> 9;
+	__u64 sector = req->offset >> SECTOR_SHIFT;
 	int i;
 
-	if(req->length > (sizeof(req->sector_mask) * 8) << 9)
+	if (req->length > (sizeof(req->sector_mask) * 8) << SECTOR_SHIFT)
 		panic("Operation too long");
 
-	if(req->op == UBD_READ) {
-		for(i = 0; i < req->length >> 9; i++){
+	if (req_op(req->req) == REQ_OP_READ) {
+		for (i = 0; i < req->length >> SECTOR_SHIFT; i++) {
 			if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
 				ubd_set_bit(i, (unsigned char *)
 					    &req->sector_mask);
@@ -1290,123 +1309,108 @@
 			   req->bitmap_words, bitmap_len);
 }
 
-/* Called with dev->lock held */
-static void prepare_request(struct request *req, struct io_thread_req *io_req,
-			    unsigned long long offset, int page_offset,
-			    int len, struct page *page)
+static int ubd_queue_one_vec(struct blk_mq_hw_ctx *hctx, struct request *req,
+		u64 off, struct bio_vec *bvec)
 {
-	struct gendisk *disk = req->rq_disk;
-	struct ubd *ubd_dev = disk->private_data;
-
-	io_req->req = req;
-	io_req->fds[0] = (ubd_dev->cow.file != NULL) ? ubd_dev->cow.fd :
-		ubd_dev->fd;
-	io_req->fds[1] = ubd_dev->fd;
-	io_req->cow_offset = -1;
-	io_req->offset = offset;
-	io_req->length = len;
-	io_req->error = 0;
-	io_req->sector_mask = 0;
-
-	io_req->op = (rq_data_dir(req) == READ) ? UBD_READ : UBD_WRITE;
-	io_req->offsets[0] = 0;
-	io_req->offsets[1] = ubd_dev->cow.data_offset;
-	io_req->buffer = page_address(page) + page_offset;
-	io_req->sectorsize = 1 << 9;
-
-	if(ubd_dev->cow.file != NULL)
-		cowify_req(io_req, ubd_dev->cow.bitmap,
-			   ubd_dev->cow.bitmap_offset, ubd_dev->cow.bitmap_len);
-
-}
-
-/* Called with dev->lock held */
-static void prepare_flush_request(struct request *req,
-				  struct io_thread_req *io_req)
-{
-	struct gendisk *disk = req->rq_disk;
-	struct ubd *ubd_dev = disk->private_data;
-
-	io_req->req = req;
-	io_req->fds[0] = (ubd_dev->cow.file != NULL) ? ubd_dev->cow.fd :
-		ubd_dev->fd;
-	io_req->op = UBD_FLUSH;
-}
-
-static bool submit_request(struct io_thread_req *io_req, struct ubd *dev)
-{
-	int n = os_write_file(thread_fd, &io_req,
-			     sizeof(io_req));
-	if (n != sizeof(io_req)) {
-		if (n != -EAGAIN)
-			printk("write to io thread failed, "
-			       "errno = %d\n", -n);
-		else if (list_empty(&dev->restart))
-			list_add(&dev->restart, &restart);
-
-		kfree(io_req);
-		return false;
-	}
-	return true;
-}
-
-/* Called with dev->lock held */
-static void do_ubd_request(struct request_queue *q)
-{
+	struct ubd *dev = hctx->queue->queuedata;
 	struct io_thread_req *io_req;
-	struct request *req;
+	int ret;
 
-	while(1){
-		struct ubd *dev = q->queuedata;
-		if(dev->request == NULL){
-			struct request *req = blk_fetch_request(q);
-			if(req == NULL)
-				return;
+	io_req = kmalloc(sizeof(struct io_thread_req), GFP_ATOMIC);
+	if (!io_req)
+		return -ENOMEM;
 
-			dev->request = req;
-			dev->rq_pos = blk_rq_pos(req);
-			dev->start_sg = 0;
-			dev->end_sg = blk_rq_map_sg(q, req, dev->sg);
-		}
+	io_req->req = req;
+	if (dev->cow.file)
+		io_req->fds[0] = dev->cow.fd;
+	else
+		io_req->fds[0] = dev->fd;
+	io_req->error = 0;
 
-		req = dev->request;
-
-		if (req_op(req) == REQ_OP_FLUSH) {
-			io_req = kmalloc(sizeof(struct io_thread_req),
-					 GFP_ATOMIC);
-			if (io_req == NULL) {
-				if (list_empty(&dev->restart))
-					list_add(&dev->restart, &restart);
-				return;
-			}
-			prepare_flush_request(req, io_req);
-			if (submit_request(io_req, dev) == false)
-				return;
-		}
-
-		while(dev->start_sg < dev->end_sg){
-			struct scatterlist *sg = &dev->sg[dev->start_sg];
-
-			io_req = kmalloc(sizeof(struct io_thread_req),
-					 GFP_ATOMIC);
-			if(io_req == NULL){
-				if(list_empty(&dev->restart))
-					list_add(&dev->restart, &restart);
-				return;
-			}
-			prepare_request(req, io_req,
-					(unsigned long long)dev->rq_pos << 9,
-					sg->offset, sg->length, sg_page(sg));
-
-			if (submit_request(io_req, dev) == false)
-				return;
-
-			dev->rq_pos += sg->length >> 9;
-			dev->start_sg++;
-		}
-		dev->end_sg = 0;
-		dev->request = NULL;
+	if (bvec != NULL) {
+		io_req->buffer = page_address(bvec->bv_page) + bvec->bv_offset;
+		io_req->length = bvec->bv_len;
+	} else {
+		io_req->buffer = NULL;
+		io_req->length = blk_rq_bytes(req);
 	}
+
+	io_req->sectorsize = SECTOR_SIZE;
+	io_req->fds[1] = dev->fd;
+	io_req->cow_offset = -1;
+	io_req->offset = off;
+	io_req->sector_mask = 0;
+	io_req->offsets[0] = 0;
+	io_req->offsets[1] = dev->cow.data_offset;
+
+	if (dev->cow.file)
+		cowify_req(io_req, dev->cow.bitmap,
+			   dev->cow.bitmap_offset, dev->cow.bitmap_len);
+
+	ret = os_write_file(thread_fd, &io_req, sizeof(io_req));
+	if (ret != sizeof(io_req)) {
+		if (ret != -EAGAIN)
+			pr_err("write to io thread failed: %d\n", -ret);
+		kfree(io_req);
+	}
+	return ret;
+}
+
+static int queue_rw_req(struct blk_mq_hw_ctx *hctx, struct request *req)
+{
+	struct req_iterator iter;
+	struct bio_vec bvec;
+	int ret;
+	u64 off = (u64)blk_rq_pos(req) << SECTOR_SHIFT;
+
+	rq_for_each_segment(bvec, req, iter) {
+		ret = ubd_queue_one_vec(hctx, req, off, &bvec);
+		if (ret < 0)
+			return ret;
+		off += bvec.bv_len;
+	}
+	return 0;
+}
+
+static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				 const struct blk_mq_queue_data *bd)
+{
+	struct ubd *ubd_dev = hctx->queue->queuedata;
+	struct request *req = bd->rq;
+	int ret = 0, res = BLK_STS_OK;
+
+	blk_mq_start_request(req);
+
+	spin_lock_irq(&ubd_dev->lock);
+
+	switch (req_op(req)) {
+	/* operations with no lentgth/offset arguments */
+	case REQ_OP_FLUSH:
+		ret = ubd_queue_one_vec(hctx, req, 0, NULL);
+		break;
+	case REQ_OP_READ:
+	case REQ_OP_WRITE:
+		ret = queue_rw_req(hctx, req);
+		break;
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		ret = ubd_queue_one_vec(hctx, req, (u64)blk_rq_pos(req) << 9, NULL);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		res = BLK_STS_NOTSUPP;
+	}
+
+	spin_unlock_irq(&ubd_dev->lock);
+
+	if (ret < 0) {
+		if (ret == -ENOMEM)
+			res = BLK_STS_RESOURCE;
+		else
+			res = BLK_STS_DEV_RESOURCE;
+	}
+
+	return res;
 }
 
 static int ubd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
@@ -1451,39 +1455,60 @@
 	return -EINVAL;
 }
 
+static int map_error(int error_code)
+{
+	switch (error_code) {
+	case 0:
+		return BLK_STS_OK;
+	case ENOSYS:
+	case EOPNOTSUPP:
+		return BLK_STS_NOTSUPP;
+	case ENOSPC:
+		return BLK_STS_NOSPC;
+	}
+	return BLK_STS_IOERR;
+}
+
+/*
+ * Everything from here onwards *IS NOT PART OF THE KERNEL*
+ *
+ * The following functions are part of UML hypervisor code.
+ * All functions from here onwards are executed as a helper
+ * thread and are not allowed to execute any kernel functions.
+ *
+ * Any communication must occur strictly via shared memory and IPC.
+ *
+ * Do not add printks, locks, kernel memory operations, etc - it
+ * will result in unpredictable behaviour and/or crashes.
+ */
+
 static int update_bitmap(struct io_thread_req *req)
 {
 	int n;
 
 	if(req->cow_offset == -1)
-		return 0;
+		return map_error(0);
 
 	n = os_pwrite_file(req->fds[1], &req->bitmap_words,
 			  sizeof(req->bitmap_words), req->cow_offset);
-	if(n != sizeof(req->bitmap_words)){
-		printk("do_io - bitmap update failed, err = %d fd = %d\n", -n,
-		       req->fds[1]);
-		return 1;
-	}
+	if (n != sizeof(req->bitmap_words))
+		return map_error(-n);
 
-	return 0;
+	return map_error(0);
 }
 
 static void do_io(struct io_thread_req *req)
 {
-	char *buf;
+	char *buf = NULL;
 	unsigned long len;
 	int n, nsectors, start, end, bit;
 	__u64 off;
 
-	if (req->op == UBD_FLUSH) {
+	/* FLUSH is really a special case, we cannot "case" it with others */
+
+	if (req_op(req->req) == REQ_OP_FLUSH) {
 		/* fds[0] is always either the rw image or our cow file */
-		n = os_sync_file(req->fds[0]);
-		if (n != 0) {
-			printk("do_io - sync failed err = %d "
-			       "fd = %d\n", -n, req->fds[0]);
-			req->error = 1;
-		}
+		req->error = map_error(-os_sync_file(req->fds[0]));
 		return;
 	}
 
@@ -1500,30 +1525,42 @@
 		off = req->offset + req->offsets[bit] +
 			start * req->sectorsize;
 		len = (end - start) * req->sectorsize;
-		buf = &req->buffer[start * req->sectorsize];
+		if (req->buffer != NULL)
+			buf = &req->buffer[start * req->sectorsize];
 
-		if(req->op == UBD_READ){
+		switch (req_op(req->req)) {
+		case REQ_OP_READ:
 			n = 0;
 			do {
 				buf = &buf[n];
 				len -= n;
 				n = os_pread_file(req->fds[bit], buf, len, off);
 				if (n < 0) {
-					printk("do_io - read failed, err = %d "
-					       "fd = %d\n", -n, req->fds[bit]);
-					req->error = 1;
+					req->error = map_error(-n);
 					return;
 				}
 			} while((n < len) && (n != 0));
 			if (n < len) memset(&buf[n], 0, len - n);
-		} else {
+			break;
+		case REQ_OP_WRITE:
 			n = os_pwrite_file(req->fds[bit], buf, len, off);
 			if(n != len){
-				printk("do_io - write failed err = %d "
-				       "fd = %d\n", -n, req->fds[bit]);
-				req->error = 1;
+				req->error = map_error(-n);
 				return;
 			}
+			break;
+		case REQ_OP_DISCARD:
+		case REQ_OP_WRITE_ZEROES:
+			n = os_falloc_punch(req->fds[bit], off, len);
+			if (n) {
+				req->error = map_error(-n);
+				return;
+			}
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			req->error = BLK_STS_NOTSUPP;
+			return;
 		}
 
 		start = end;
@@ -1558,11 +1595,6 @@
 			if (n == -EAGAIN) {
 				ubd_read_poll(-1);
 				continue;
-			} else {
-				printk("io_thread - read failed, fd = %d, "
-				       "err = %d,"
-				       "reminder = %d\n",
-				       kernel_fd, -n, io_remainder_size);
 			}
 		}
 
@@ -1577,11 +1609,6 @@
 			res = os_write_file(kernel_fd, ((char *) io_req_buffer) + written, n);
 			if (res >= 0) {
 				written += res;
-			} else {
-				if (res != -EAGAIN) {
-					printk("io_thread - write failed, fd = %d, "
-					       "err = %d\n", kernel_fd, -n);
-				}
 			}
 			if (written < n) {
 				ubd_write_poll(-1);
diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index 6f74479..a1afe41 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -1,8 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2016 Anton Ivanov (aivanov@brocade.com)
  * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
  * Copyright (C) 2001 Ridgerun,Inc (glonnon@ridgerun.com)
- * Licensed under the GPL
  */
 
 #include <stddef.h>
diff --git a/arch/um/drivers/umcast.h b/arch/um/drivers/umcast.h
index c190c64..fe39bee 100644
--- a/arch/um/drivers/umcast.h
+++ b/arch/um/drivers/umcast.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __DRIVERS_UMCAST_H
diff --git a/arch/um/drivers/umcast_kern.c b/arch/um/drivers/umcast_kern.c
index f5ba6e3..595a54f 100644
--- a/arch/um/drivers/umcast_kern.c
+++ b/arch/um/drivers/umcast_kern.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * user-mode-linux networking multicast transport
  * Copyright (C) 2001 by Harald Welte <laforge@gnumonks.org>
@@ -8,7 +9,6 @@
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
  *
- * Licensed under the GPL.
  */
 
 #include <linux/init.h>
diff --git a/arch/um/drivers/umcast_user.c b/arch/um/drivers/umcast_user.c
index 6074184..b50b13c 100644
--- a/arch/um/drivers/umcast_user.c
+++ b/arch/um/drivers/umcast_user.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * user-mode-linux networking multicast transport
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
@@ -8,7 +9,6 @@
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
  *
- * Licensed under the GPL.
  *
  */
 
diff --git a/arch/um/drivers/vde.h b/arch/um/drivers/vde.h
index fc3a059..cab0379 100644
--- a/arch/um/drivers/vde.h
+++ b/arch/um/drivers/vde.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2007 Luca Bigliardi (shammash@artha.org).
- * Licensed under the GPL.
  */
 
 #ifndef __UM_VDE_H__
diff --git a/arch/um/drivers/vde_kern.c b/arch/um/drivers/vde_kern.c
index 6a365fa..bc6f22c 100644
--- a/arch/um/drivers/vde_kern.c
+++ b/arch/um/drivers/vde_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Luca Bigliardi (shammash@artha.org).
- * Licensed under the GPL.
  *
  * Transport usage:
  *  ethN=vde,<vde_switch>,<mac addr>,<port>,<group>,<mode>,<description>
diff --git a/arch/um/drivers/vde_user.c b/arch/um/drivers/vde_user.c
index 64cb630..bc7dc4e 100644
--- a/arch/um/drivers/vde_user.c
+++ b/arch/um/drivers/vde_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Luca Bigliardi (shammash@artha.org).
- * Licensed under the GPL.
  */
 
 #include <stddef.h>
diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
index 50ee3bb..769ffbd 100644
--- a/arch/um/drivers/vector_kern.c
+++ b/arch/um/drivers/vector_kern.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 - Cambridge Greys Limited
  * Copyright (C) 2011 - 2014 Cisco Systems Inc
@@ -5,11 +6,10 @@
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
 #include <linux/version.h>
-#include <linux/bootmem.h>
+#include <linux/memblock.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
 #include <linux/inetdevice.h>
@@ -76,6 +76,7 @@
 #define DEFAULT_VECTOR_SIZE 64
 #define TX_SMALL_PACKET 128
 #define MAX_IOV_SIZE (MAX_SKB_FRAGS + 1)
+#define MAX_ITERATIONS 64
 
 static const struct {
 	const char string[ETH_GSTRING_LEN];
@@ -121,7 +122,8 @@
 
 	if (mtu != NULL) {
 		if (kstrtoul(mtu, 10, &result) == 0)
-			return result;
+			if ((result < (1 << 16) - 1) && (result >= 576))
+				return result;
 	}
 	return ETH_MAX_PACKET;
 }
@@ -186,6 +188,8 @@
 
 
 	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
+		return 0;
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
 		return (vec_rx | VECTOR_BPF);
 	if (strncmp(transport, TRANS_RAW, TRANS_RAW_LEN) == 0)
 		return (vec_rx | vec_tx | VECTOR_QDISC_BYPASS);
@@ -415,6 +419,7 @@
 					if (net_ratelimit())
 						netdev_err(vp->dev, "sendmmsg err=%i\n",
 							result);
+					vp->in_error = true;
 					result = send_len;
 				}
 				if (result > 0) {
@@ -842,6 +847,10 @@
 	}
 
 	pkt_len = uml_vector_recvmsg(vp->fds->rx_fd, &hdr, 0);
+	if (pkt_len < 0) {
+		vp->in_error = true;
+		return pkt_len;
+	}
 
 	if (skb != NULL) {
 		if (pkt_len > vp->header_size) {
@@ -888,12 +897,16 @@
 
 	if (iov_count < 1)
 		goto drop;
+
 	pkt_len = uml_vector_writev(
 		vp->fds->tx_fd,
 		(struct iovec *) &iov,
 		iov_count
 	);
 
+	if (pkt_len < 0)
+		goto drop;
+
 	netif_trans_update(vp->dev);
 	netif_wake_queue(vp->dev);
 
@@ -908,6 +921,8 @@
 drop:
 	vp->dev->stats.tx_dropped++;
 	consume_skb(skb);
+	if (pkt_len < 0)
+		vp->in_error = true;
 	return pkt_len;
 }
 
@@ -936,6 +951,9 @@
 	packet_count = uml_vector_recvmmsg(
 		vp->fds->rx_fd, qi->mmsg_vector, qi->max_depth, 0);
 
+	if (packet_count < 0)
+		vp->in_error = true;
+
 	if (packet_count <= 0)
 		return packet_count;
 
@@ -1005,15 +1023,18 @@
 static void vector_rx(struct vector_private *vp)
 {
 	int err;
+	int iter = 0;
 
 	if ((vp->options & VECTOR_RX) > 0)
-		while ((err = vector_mmsg_rx(vp)) > 0)
-			;
+		while (((err = vector_mmsg_rx(vp)) > 0) && (iter < MAX_ITERATIONS))
+			iter++;
 	else
-		while ((err = vector_legacy_rx(vp)) > 0)
-			;
+		while (((err = vector_legacy_rx(vp)) > 0) && (iter < MAX_ITERATIONS))
+			iter++;
 	if ((err != 0) && net_ratelimit())
 		netdev_err(vp->dev, "vector_rx: error(%d)\n", err);
+	if (iter == MAX_ITERATIONS)
+		netdev_err(vp->dev, "vector_rx: device stuck, remote end may have closed the connection\n");
 }
 
 static int vector_net_start_xmit(struct sk_buff *skb, struct net_device *dev)
@@ -1021,6 +1042,13 @@
 	struct vector_private *vp = netdev_priv(dev);
 	int queue_depth = 0;
 
+	if (vp->in_error) {
+		deactivate_fd(vp->fds->rx_fd, vp->rx_irq);
+		if ((vp->fds->rx_fd != vp->fds->tx_fd) && (vp->tx_irq != 0))
+			deactivate_fd(vp->fds->tx_fd, vp->tx_irq);
+		return NETDEV_TX_BUSY;
+	}
+
 	if ((vp->options & VECTOR_TX) == 0) {
 		writev_tx(vp, skb);
 		return NETDEV_TX_OK;
@@ -1043,7 +1071,7 @@
 		vector_send(vp->tx_queue);
 		return NETDEV_TX_OK;
 	}
-	if (skb->xmit_more) {
+	if (netdev_xmit_more()) {
 		mod_timer(&vp->tl, vp->coalesce);
 		return NETDEV_TX_OK;
 	}
@@ -1118,16 +1146,11 @@
 		os_close_file(vp->fds->tx_fd);
 		vp->fds->tx_fd = -1;
 	}
-	if (vp->bpf != NULL)
-		kfree(vp->bpf);
-	if (vp->fds->remote_addr != NULL)
-		kfree(vp->fds->remote_addr);
-	if (vp->transport_data != NULL)
-		kfree(vp->transport_data);
-	if (vp->header_rxbuffer != NULL)
-		kfree(vp->header_rxbuffer);
-	if (vp->header_txbuffer != NULL)
-		kfree(vp->header_txbuffer);
+	kfree(vp->bpf);
+	kfree(vp->fds->remote_addr);
+	kfree(vp->transport_data);
+	kfree(vp->header_rxbuffer);
+	kfree(vp->header_txbuffer);
 	if (vp->rx_queue != NULL)
 		destroy_queue(vp->rx_queue);
 	if (vp->tx_queue != NULL)
@@ -1136,6 +1159,7 @@
 	vp->fds = NULL;
 	spin_lock_irqsave(&vp->lock, flags);
 	vp->opened = false;
+	vp->in_error = false;
 	spin_unlock_irqrestore(&vp->lock, flags);
 	return 0;
 }
@@ -1503,7 +1527,8 @@
 		.transport_data		= NULL,
 		.in_write_poll		= false,
 		.coalesce		= 2,
-		.req_size		= get_req_size(def)
+		.req_size		= get_req_size(def),
+		.in_error		= false
 		});
 
 	dev->features = dev->hw_features = (NETIF_F_SG | NETIF_F_FRAGLIST);
@@ -1580,7 +1605,10 @@
 				 str, error);
 		return 1;
 	}
-	new = alloc_bootmem(sizeof(*new));
+	new = memblock_alloc(sizeof(*new), SMP_CACHE_BYTES);
+	if (!new)
+		panic("%s: Failed to allocate %zu bytes\n", __func__,
+		      sizeof(*new));
 	INIT_LIST_HEAD(&new->list);
 	new->unit = n;
 	new->arguments = str;
diff --git a/arch/um/drivers/vector_kern.h b/arch/um/drivers/vector_kern.h
index 0b0a767..4d292e6 100644
--- a/arch/um/drivers/vector_kern.h
+++ b/arch/um/drivers/vector_kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_VECTOR_KERN_H
@@ -116,6 +116,7 @@
 	bool rexmit_scheduled;
 	bool opened;
 	bool in_write_poll;
+	bool in_error;
 
 	/* ethtool stats */
 
diff --git a/arch/um/drivers/vector_transports.c b/arch/um/drivers/vector_transports.c
index 77e4ebc..0794d23 100644
--- a/arch/um/drivers/vector_transports.c
+++ b/arch/um/drivers/vector_transports.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 - Cambridge Greys Limited
  * Copyright (C) 2011 - 2014 Cisco Systems Inc
- * Licensed under the GPL.
  */
 
 #include <linux/etherdevice.h>
@@ -418,7 +418,7 @@
 	return 0;
 }
 
-static int build_tap_transport_data(struct vector_private *vp)
+static int build_hybrid_transport_data(struct vector_private *vp)
 {
 	if (uml_raw_enable_vnet_headers(vp->fds->rx_fd)) {
 		vp->form_header = &raw_form_header;
@@ -432,7 +432,7 @@
 				NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
 		netdev_info(
 			vp->dev,
-			"tap/raw: using vnet headers for tso and tx/rx checksum"
+			"tap/raw hybrid: using vnet headers for tso and tx/rx checksum"
 		);
 	} else {
 		return 0; /* do not try to enable tap too if raw failed */
@@ -442,6 +442,38 @@
 	return -1;
 }
 
+static int build_tap_transport_data(struct vector_private *vp)
+{
+	/* "Pure" tap uses the same fd for rx and tx */
+	if (uml_tap_enable_vnet_headers(vp->fds->tx_fd)) {
+		vp->form_header = &raw_form_header;
+		vp->verify_header = &raw_verify_header;
+		vp->header_size = sizeof(struct virtio_net_hdr);
+		vp->rx_header_size = sizeof(struct virtio_net_hdr);
+		vp->dev->hw_features |=
+			(NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		vp->dev->features |=
+			(NETIF_F_RXCSUM | NETIF_F_HW_CSUM |
+				NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		netdev_info(
+			vp->dev,
+			"tap: using vnet headers for tso and tx/rx checksum"
+		);
+		return 0;
+	}
+	return -1;
+}
+
+
+static int build_bess_transport_data(struct vector_private *vp)
+{
+	vp->form_header = NULL;
+	vp->verify_header = NULL;
+	vp->header_size = 0;
+	vp->rx_header_size = 0;
+	return 0;
+}
+
 int build_transport_data(struct vector_private *vp)
 {
 	char *transport = uml_vector_fetch_arg(vp->parsed, "transport");
@@ -454,6 +486,10 @@
 		return build_raw_transport_data(vp);
 	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
 		return build_tap_transport_data(vp);
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
+		return build_hybrid_transport_data(vp);
+	if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
+		return build_bess_transport_data(vp);
 	return 0;
 }
 
diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
index 4d6a78e..e2c969b 100644
--- a/arch/um/drivers/vector_user.c
+++ b/arch/um/drivers/vector_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
@@ -16,15 +16,15 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-#include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/un.h>
 #include <net/ethernet.h>
 #include <netinet/ip.h>
 #include <netinet/ether.h>
 #include <linux/if_ether.h>
 #include <linux/if_packet.h>
-#include <sys/socket.h>
 #include <sys/wait.h>
+#include <sys/uio.h>
 #include <linux/virtio_net.h>
 #include <netdb.h>
 #include <stdlib.h>
@@ -34,7 +34,8 @@
 
 #define ID_GRE 0
 #define ID_L2TPV3 1
-#define ID_MAX 1
+#define ID_BESS 2
+#define ID_MAX 2
 
 #define TOKEN_IFNAME "ifname"
 
@@ -44,8 +45,11 @@
 #define VNET_HDR_FAIL "could not enable vnet headers on fd %d"
 #define TUN_GET_F_FAIL "tapraw: TUNGETFEATURES failed: %s"
 #define L2TPV3_BIND_FAIL "l2tpv3_open : could not bind socket err=%i"
+#define UNIX_BIND_FAIL "unix_open : could not bind socket err=%i"
 #define BPF_ATTACH_FAIL "Failed to attach filter size %d to %d, err %d\n"
 
+#define MAX_UN_LEN 107
+
 /* This is very ugly and brute force lookup, but it is done
  * only once at initialization so not worth doing hashes or
  * anything more intelligent
@@ -115,12 +119,76 @@
 
 #define PATH_NET_TUN "/dev/net/tun"
 
-static struct vector_fds *user_init_tap_fds(struct arglist *ifspec)
+
+static int create_tap_fd(char *iface)
+{
+	struct ifreq ifr;
+	int fd = -1;
+	int err = -ENOMEM, offload;
+
+	fd = open(PATH_NET_TUN, O_RDWR);
+	if (fd < 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to open tun device\n");
+		goto tap_fd_cleanup;
+	}
+	memset(&ifr, 0, sizeof(ifr));
+	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
+	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
+
+	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
+	if (err != 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to select tap interface\n");
+		goto tap_fd_cleanup;
+	}
+
+	offload = TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6;
+	ioctl(fd, TUNSETOFFLOAD, offload);
+	return fd;
+tap_fd_cleanup:
+	if (fd >= 0)
+		os_close_file(fd);
+	return err;
+}
+
+static int create_raw_fd(char *iface, int flags, int proto)
 {
 	struct ifreq ifr;
 	int fd = -1;
 	struct sockaddr_ll sock;
-	int err = -ENOMEM, offload;
+	int err = -ENOMEM;
+
+	fd = socket(AF_PACKET, SOCK_RAW, flags);
+	if (fd == -1) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
+	if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+
+	sock.sll_family = AF_PACKET;
+	sock.sll_protocol = htons(proto);
+	sock.sll_ifindex = ifr.ifr_ifindex;
+
+	if (bind(fd,
+		(struct sockaddr *) &sock, sizeof(struct sockaddr_ll)) < 0) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+	return fd;
+raw_fd_cleanup:
+	printk(UM_KERN_ERR "user_init_raw: init failed, error %d", err);
+	if (fd >= 0)
+		os_close_file(fd);
+	return err;
+}
+
+static struct vector_fds *user_init_tap_fds(struct arglist *ifspec)
+{
+	int fd = -1;
 	char *iface;
 	struct vector_fds *result = NULL;
 
@@ -142,117 +210,167 @@
 
 	/* TAP */
 
-	fd = open(PATH_NET_TUN, O_RDWR);
+	fd = create_tap_fd(iface);
 	if (fd < 0) {
-		printk(UM_KERN_ERR "uml_tap: failed to open tun device\n");
+		printk(UM_KERN_ERR "uml_tap: failed to create tun interface\n");
 		goto tap_cleanup;
 	}
 	result->tx_fd = fd;
-	memset(&ifr, 0, sizeof(ifr));
-	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
-	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
-
-	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
-	if (err != 0) {
-		printk(UM_KERN_ERR "uml_tap: failed to select tap interface\n");
-		goto tap_cleanup;
-	}
-
-	offload = TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6;
-	ioctl(fd, TUNSETOFFLOAD, offload);
-
-	/* RAW */
-
-	fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
-	if (fd == -1) {
-		printk(UM_KERN_ERR
-			"uml_tap: failed to create socket: %i\n", -errno);
-		goto tap_cleanup;
-	}
 	result->rx_fd = fd;
-	memset(&ifr, 0, sizeof(ifr));
-	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
-	if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
-		printk(UM_KERN_ERR
-			"uml_tap: failed to set interface: %i\n", -errno);
-		goto tap_cleanup;
-	}
-
-	sock.sll_family = AF_PACKET;
-	sock.sll_protocol = htons(ETH_P_ALL);
-	sock.sll_ifindex = ifr.ifr_ifindex;
-
-	if (bind(fd,
-		(struct sockaddr *) &sock, sizeof(struct sockaddr_ll)) < 0) {
-		printk(UM_KERN_ERR
-			"user_init_tap: failed to bind raw pair, err %d\n",
-				-errno);
-		goto tap_cleanup;
-	}
 	return result;
 tap_cleanup:
-	printk(UM_KERN_ERR "user_init_tap: init failed, error %d", err);
-	if (result != NULL) {
-		if (result->rx_fd >= 0)
-			os_close_file(result->rx_fd);
-		if (result->tx_fd >= 0)
-			os_close_file(result->tx_fd);
+	printk(UM_KERN_ERR "user_init_tap: init failed, error %d", fd);
+	if (result != NULL)
 		kfree(result);
-	}
 	return NULL;
 }
 
+static struct vector_fds *user_init_hybrid_fds(struct arglist *ifspec)
+{
+	char *iface;
+	struct vector_fds *result = NULL;
+
+	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
+	if (iface == NULL) {
+		printk(UM_KERN_ERR "uml_tap: failed to parse interface spec\n");
+		goto hybrid_cleanup;
+	}
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "uml_tap: failed to allocate file descriptors\n");
+		goto hybrid_cleanup;
+	}
+	result->rx_fd = -1;
+	result->tx_fd = -1;
+	result->remote_addr = NULL;
+	result->remote_addr_size = 0;
+
+	/* TAP */
+
+	result->tx_fd = create_tap_fd(iface);
+	if (result->tx_fd < 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to create tun interface: %i\n", result->tx_fd);
+		goto hybrid_cleanup;
+	}
+
+	/* RAW */
+
+	result->rx_fd = create_raw_fd(iface, ETH_P_ALL, ETH_P_ALL);
+	if (result->rx_fd == -1) {
+		printk(UM_KERN_ERR
+			"uml_tap: failed to create paired raw socket: %i\n", result->rx_fd);
+		goto hybrid_cleanup;
+	}
+	return result;
+hybrid_cleanup:
+	printk(UM_KERN_ERR "user_init_hybrid: init failed");
+	if (result != NULL)
+		kfree(result);
+	return NULL;
+}
+
+static struct vector_fds *user_init_unix_fds(struct arglist *ifspec, int id)
+{
+	int fd = -1;
+	int socktype;
+	char *src, *dst;
+	struct vector_fds *result = NULL;
+	struct sockaddr_un *local_addr = NULL, *remote_addr = NULL;
+
+	src = uml_vector_fetch_arg(ifspec, "src");
+	dst = uml_vector_fetch_arg(ifspec, "dst");
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "unix open:cannot allocate remote addr");
+		goto unix_cleanup;
+	}
+	remote_addr = uml_kmalloc(sizeof(struct sockaddr_un), UM_GFP_KERNEL);
+	if (remote_addr == NULL) {
+		printk(UM_KERN_ERR "unix open:cannot allocate remote addr");
+		goto unix_cleanup;
+	}
+
+	switch (id) {
+	case ID_BESS:
+		socktype = SOCK_SEQPACKET;
+		if ((src != NULL) && (strlen(src) <= MAX_UN_LEN)) {
+			local_addr = uml_kmalloc(sizeof(struct sockaddr_un), UM_GFP_KERNEL);
+			if (local_addr == NULL) {
+				printk(UM_KERN_ERR "bess open:cannot allocate local addr");
+				goto unix_cleanup;
+			}
+			local_addr->sun_family = AF_UNIX;
+			memcpy(local_addr->sun_path, src, strlen(src) + 1);
+		}
+		if ((dst == NULL) || (strlen(dst) > MAX_UN_LEN))
+			goto unix_cleanup;
+		remote_addr->sun_family = AF_UNIX;
+		memcpy(remote_addr->sun_path, dst, strlen(dst) + 1);
+		break;
+	default:
+		printk(KERN_ERR "Unsupported unix socket type\n");
+		return NULL;
+	}
+
+	fd = socket(AF_UNIX, socktype, 0);
+	if (fd == -1) {
+		printk(UM_KERN_ERR
+			"unix open: could not open socket, error = %d",
+			-errno
+		);
+		goto unix_cleanup;
+	}
+	if (local_addr != NULL) {
+		if (bind(fd, (struct sockaddr *) local_addr, sizeof(struct sockaddr_un))) {
+			printk(UM_KERN_ERR UNIX_BIND_FAIL, errno);
+			goto unix_cleanup;
+		}
+	}
+	switch (id) {
+	case ID_BESS:
+		if (connect(fd, remote_addr, sizeof(struct sockaddr_un)) < 0) {
+			printk(UM_KERN_ERR "bess open:cannot connect to %s %i", remote_addr->sun_path, -errno);
+			goto unix_cleanup;
+		}
+		break;
+	}
+	result->rx_fd = fd;
+	result->tx_fd = fd;
+	result->remote_addr_size = sizeof(struct sockaddr_un);
+	result->remote_addr = remote_addr;
+	return result;
+unix_cleanup:
+	if (fd >= 0)
+		os_close_file(fd);
+	if (remote_addr != NULL)
+		kfree(remote_addr);
+	if (result != NULL)
+		kfree(result);
+	return NULL;
+}
 
 static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
 {
-	struct ifreq ifr;
 	int rxfd = -1, txfd = -1;
-	struct sockaddr_ll sock;
 	int err = -ENOMEM;
 	char *iface;
 	struct vector_fds *result = NULL;
 
 	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
 	if (iface == NULL)
-		goto cleanup;
+		goto raw_cleanup;
 
-	rxfd = socket(AF_PACKET, SOCK_RAW, ETH_P_ALL);
+	rxfd = create_raw_fd(iface, ETH_P_ALL, ETH_P_ALL);
 	if (rxfd == -1) {
 		err = -errno;
-		goto cleanup;
+		goto raw_cleanup;
 	}
-	txfd = socket(AF_PACKET, SOCK_RAW, 0); /* Turn off RX on this fd */
+	txfd = create_raw_fd(iface, 0, ETH_P_IP); /* Turn off RX on this fd */
 	if (txfd == -1) {
 		err = -errno;
-		goto cleanup;
+		goto raw_cleanup;
 	}
-	memset(&ifr, 0, sizeof(ifr));
-	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
-	if (ioctl(rxfd, SIOCGIFINDEX, (void *) &ifr) < 0) {
-		err = -errno;
-		goto cleanup;
-	}
-
-	sock.sll_family = AF_PACKET;
-	sock.sll_protocol = htons(ETH_P_ALL);
-	sock.sll_ifindex = ifr.ifr_ifindex;
-
-	if (bind(rxfd,
-		(struct sockaddr *) &sock, sizeof(struct sockaddr_ll)) < 0) {
-		err = -errno;
-		goto cleanup;
-	}
-
-	sock.sll_family = AF_PACKET;
-	sock.sll_protocol = htons(ETH_P_IP);
-	sock.sll_ifindex = ifr.ifr_ifindex;
-
-	if (bind(txfd,
-		(struct sockaddr *) &sock, sizeof(struct sockaddr_ll)) < 0) {
-		err = -errno;
-		goto cleanup;
-	}
-
 	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
 	if (result != NULL) {
 		result->rx_fd = rxfd;
@@ -261,12 +379,8 @@
 		result->remote_addr_size = 0;
 	}
 	return result;
-cleanup:
+raw_cleanup:
 	printk(UM_KERN_ERR "user_init_raw: init failed, error %d", err);
-	if (rxfd >= 0)
-		os_close_file(rxfd);
-	if (txfd >= 0)
-		os_close_file(txfd);
 	if (result != NULL)
 		kfree(result);
 	return NULL;
@@ -434,8 +548,7 @@
 	if (fd >= 0)
 		os_close_file(fd);
 	if (result != NULL) {
-		if (result->remote_addr != NULL)
-			kfree(result->remote_addr);
+		kfree(result->remote_addr);
 		kfree(result);
 	}
 	return NULL;
@@ -459,12 +572,16 @@
 	}
 	if (strncmp(transport, TRANS_RAW, TRANS_RAW_LEN) == 0)
 		return user_init_raw_fds(parsed);
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
+		return user_init_hybrid_fds(parsed);
 	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
 		return user_init_tap_fds(parsed);
 	if (strncmp(transport, TRANS_GRE, TRANS_GRE_LEN) == 0)
 		return user_init_socket_fds(parsed, ID_GRE);
 	if (strncmp(transport, TRANS_L2TPV3, TRANS_L2TPV3_LEN) == 0)
 		return user_init_socket_fds(parsed, ID_L2TPV3);
+	if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
+		return user_init_unix_fds(parsed, ID_BESS);
 	return NULL;
 }
 
@@ -485,8 +602,9 @@
 int uml_vector_recvmsg(int fd, void *hdr, int flags)
 {
 	int n;
+	struct msghdr *msg = (struct msghdr *) hdr;
 
-	CATCH_EINTR(n = recvmsg(fd, (struct msghdr *) hdr,  flags));
+	CATCH_EINTR(n = readv(fd, msg->msg_iov, msg->msg_iovlen));
 	if ((n < 0) && (errno == EAGAIN))
 		return 0;
 	if (n >= 0)
@@ -500,7 +618,7 @@
 	int n;
 
 	CATCH_EINTR(n = writev(fd, (struct iovec *) hdr,  iovcount));
-	if ((n < 0) && (errno == EAGAIN))
+	if ((n < 0) && ((errno == EAGAIN) || (errno == ENOBUFS)))
 		return 0;
 	if (n >= 0)
 		return n;
@@ -517,7 +635,7 @@
 	int n;
 
 	CATCH_EINTR(n = sendmmsg(fd, (struct mmsghdr *) msgvec, vlen, flags));
-	if ((n < 0) && (errno == EAGAIN))
+	if ((n < 0) && ((errno == EAGAIN) || (errno == ENOBUFS)))
 		return 0;
 	if (n >= 0)
 		return n;
diff --git a/arch/um/drivers/vector_user.h b/arch/um/drivers/vector_user.h
index d7cbff7..649ec25 100644
--- a/arch/um/drivers/vector_user.h
+++ b/arch/um/drivers/vector_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_VECTOR_USER_H
@@ -16,13 +16,18 @@
 #define TRANS_TAP "tap"
 #define TRANS_TAP_LEN strlen(TRANS_TAP)
 
-
 #define TRANS_GRE "gre"
 #define TRANS_GRE_LEN strlen(TRANS_RAW)
 
 #define TRANS_L2TPV3 "l2tpv3"
 #define TRANS_L2TPV3_LEN strlen(TRANS_L2TPV3)
 
+#define TRANS_HYBRID "hybrid"
+#define TRANS_HYBRID_LEN strlen(TRANS_HYBRID)
+
+#define TRANS_BESS "bess"
+#define TRANS_BESS_LEN strlen(TRANS_BESS)
+
 #ifndef IPPROTO_GRE
 #define IPPROTO_GRE 0x2F
 #endif
diff --git a/arch/um/drivers/vhost_user.h b/arch/um/drivers/vhost_user.h
new file mode 100644
index 0000000..45ff5ea
--- /dev/null
+++ b/arch/um/drivers/vhost_user.h
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Vhost-user protocol */
+
+#ifndef __VHOST_USER_H__
+#define __VHOST_USER_H__
+
+/* Message flags */
+#define VHOST_USER_FLAG_REPLY		BIT(2)
+#define VHOST_USER_FLAG_NEED_REPLY	BIT(3)
+/* Feature bits */
+#define VHOST_USER_F_PROTOCOL_FEATURES	30
+/* Protocol feature bits */
+#define VHOST_USER_PROTOCOL_F_REPLY_ACK		3
+#define VHOST_USER_PROTOCOL_F_SLAVE_REQ		5
+#define VHOST_USER_PROTOCOL_F_CONFIG		9
+/* Vring state index masks */
+#define VHOST_USER_VRING_INDEX_MASK	0xff
+#define VHOST_USER_VRING_POLL_MASK	BIT(8)
+
+/* Supported version */
+#define VHOST_USER_VERSION		1
+/* Supported transport features */
+#define VHOST_USER_SUPPORTED_F		BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)
+/* Supported protocol features */
+#define VHOST_USER_SUPPORTED_PROTOCOL_F	(BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG))
+
+enum vhost_user_request {
+	VHOST_USER_GET_FEATURES = 1,
+	VHOST_USER_SET_FEATURES = 2,
+	VHOST_USER_SET_OWNER = 3,
+	VHOST_USER_RESET_OWNER = 4,
+	VHOST_USER_SET_MEM_TABLE = 5,
+	VHOST_USER_SET_LOG_BASE = 6,
+	VHOST_USER_SET_LOG_FD = 7,
+	VHOST_USER_SET_VRING_NUM = 8,
+	VHOST_USER_SET_VRING_ADDR = 9,
+	VHOST_USER_SET_VRING_BASE = 10,
+	VHOST_USER_GET_VRING_BASE = 11,
+	VHOST_USER_SET_VRING_KICK = 12,
+	VHOST_USER_SET_VRING_CALL = 13,
+	VHOST_USER_SET_VRING_ERR = 14,
+	VHOST_USER_GET_PROTOCOL_FEATURES = 15,
+	VHOST_USER_SET_PROTOCOL_FEATURES = 16,
+	VHOST_USER_GET_QUEUE_NUM = 17,
+	VHOST_USER_SET_VRING_ENABLE = 18,
+	VHOST_USER_SEND_RARP = 19,
+	VHOST_USER_NET_SEND_MTU = 20,
+	VHOST_USER_SET_SLAVE_REQ_FD = 21,
+	VHOST_USER_IOTLB_MSG = 22,
+	VHOST_USER_SET_VRING_ENDIAN = 23,
+	VHOST_USER_GET_CONFIG = 24,
+	VHOST_USER_SET_CONFIG = 25,
+};
+
+enum vhost_user_slave_request {
+	VHOST_USER_SLAVE_IOTLB_MSG = 1,
+	VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2,
+	VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3,
+};
+
+struct vhost_user_header {
+	/*
+	 * Use enum vhost_user_request for outgoing messages,
+	 * uses enum vhost_user_slave_request for incoming ones.
+	 */
+	u32 request;
+	u32 flags;
+	u32 size;
+} __packed;
+
+struct vhost_user_config {
+	u32 offset;
+	u32 size;
+	u32 flags;
+	u8 payload[0]; /* Variable length */
+} __packed;
+
+struct vhost_user_vring_state {
+	u32 index;
+	u32 num;
+} __packed;
+
+struct vhost_user_vring_addr {
+	u32 index;
+	u32 flags;
+	u64 desc, used, avail, log;
+} __packed;
+
+struct vhost_user_mem_region {
+	u64 guest_addr;
+	u64 size;
+	u64 user_addr;
+	u64 mmap_offset;
+} __packed;
+
+struct vhost_user_mem_regions {
+	u32 num;
+	u32 padding;
+	struct vhost_user_mem_region regions[2]; /* Currently supporting 2 */
+} __packed;
+
+union vhost_user_payload {
+	u64 integer;
+	struct vhost_user_config config;
+	struct vhost_user_vring_state vring_state;
+	struct vhost_user_vring_addr vring_addr;
+	struct vhost_user_mem_regions mem_regions;
+};
+
+struct vhost_user_msg {
+	struct vhost_user_header header;
+	union vhost_user_payload payload;
+} __packed;
+
+#endif
diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
new file mode 100644
index 0000000..fc8c52c
--- /dev/null
+++ b/arch/um/drivers/virtio_uml.c
@@ -0,0 +1,1177 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtio vhost-user driver
+ *
+ * Copyright(c) 2019 Intel Corporation
+ *
+ * This module allows virtio devices to be used over a vhost-user socket.
+ *
+ * Guest devices can be instantiated by kernel module or command line
+ * parameters. One device will be created for each parameter. Syntax:
+ *
+ *		[virtio_uml.]device=<socket>:<virtio_id>[:<platform_id>]
+ * where:
+ *		<socket>	:= vhost-user socket path to connect
+ *		<virtio_id>	:= virtio device id (as in virtio_ids.h)
+ *		<platform_id>	:= (optional) platform device id
+ *
+ * example:
+ *		virtio_uml.device=/var/uml.socket:1
+ *
+ * Based on Virtio MMIO driver by Pawel Moll, copyright 2011-2014, ARM Ltd.
+ */
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
+#include <shared/as-layout.h>
+#include <irq_kern.h>
+#include <init.h>
+#include <os.h>
+#include "vhost_user.h"
+
+/* Workaround due to a conflict between irq_user.h and irqreturn.h */
+#ifdef IRQ_NONE
+#undef IRQ_NONE
+#endif
+
+#define MAX_SUPPORTED_QUEUE_SIZE	256
+
+#define to_virtio_uml_device(_vdev) \
+	container_of(_vdev, struct virtio_uml_device, vdev)
+
+struct virtio_uml_device {
+	struct virtio_device vdev;
+	struct platform_device *pdev;
+
+	int sock, req_fd;
+	u64 features;
+	u64 protocol_features;
+	u8 status;
+};
+
+struct virtio_uml_vq_info {
+	int kick_fd, call_fd;
+	char name[32];
+};
+
+extern unsigned long long physmem_size, highmem;
+
+#define vu_err(vu_dev, ...)	dev_err(&(vu_dev)->pdev->dev, __VA_ARGS__)
+
+/* Vhost-user protocol */
+
+static int full_sendmsg_fds(int fd, const void *buf, unsigned int len,
+			    const int *fds, unsigned int fds_num)
+{
+	int rc;
+
+	do {
+		rc = os_sendmsg_fds(fd, buf, len, fds, fds_num);
+		if (rc > 0) {
+			buf += rc;
+			len -= rc;
+			fds = NULL;
+			fds_num = 0;
+		}
+	} while (len && (rc >= 0 || rc == -EINTR));
+
+	if (rc < 0)
+		return rc;
+	return 0;
+}
+
+static int full_read(int fd, void *buf, int len)
+{
+	int rc;
+
+	do {
+		rc = os_read_file(fd, buf, len);
+		if (rc > 0) {
+			buf += rc;
+			len -= rc;
+		}
+	} while (len && (rc > 0 || rc == -EINTR));
+
+	if (rc < 0)
+		return rc;
+	if (rc == 0)
+		return -ECONNRESET;
+	return 0;
+}
+
+static int vhost_user_recv_header(int fd, struct vhost_user_msg *msg)
+{
+	return full_read(fd, msg, sizeof(msg->header));
+}
+
+static int vhost_user_recv(int fd, struct vhost_user_msg *msg,
+			   size_t max_payload_size)
+{
+	size_t size;
+	int rc = vhost_user_recv_header(fd, msg);
+
+	if (rc)
+		return rc;
+	size = msg->header.size;
+	if (size > max_payload_size)
+		return -EPROTO;
+	return full_read(fd, &msg->payload, size);
+}
+
+static int vhost_user_recv_resp(struct virtio_uml_device *vu_dev,
+				struct vhost_user_msg *msg,
+				size_t max_payload_size)
+{
+	int rc = vhost_user_recv(vu_dev->sock, msg, max_payload_size);
+
+	if (rc)
+		return rc;
+
+	if (msg->header.flags != (VHOST_USER_FLAG_REPLY | VHOST_USER_VERSION))
+		return -EPROTO;
+
+	return 0;
+}
+
+static int vhost_user_recv_u64(struct virtio_uml_device *vu_dev,
+			       u64 *value)
+{
+	struct vhost_user_msg msg;
+	int rc = vhost_user_recv_resp(vu_dev, &msg,
+				      sizeof(msg.payload.integer));
+
+	if (rc)
+		return rc;
+	if (msg.header.size != sizeof(msg.payload.integer))
+		return -EPROTO;
+	*value = msg.payload.integer;
+	return 0;
+}
+
+static int vhost_user_recv_req(struct virtio_uml_device *vu_dev,
+			       struct vhost_user_msg *msg,
+			       size_t max_payload_size)
+{
+	int rc = vhost_user_recv(vu_dev->req_fd, msg, max_payload_size);
+
+	if (rc)
+		return rc;
+
+	if ((msg->header.flags & ~VHOST_USER_FLAG_NEED_REPLY) !=
+			VHOST_USER_VERSION)
+		return -EPROTO;
+
+	return 0;
+}
+
+static int vhost_user_send(struct virtio_uml_device *vu_dev,
+			   bool need_response, struct vhost_user_msg *msg,
+			   int *fds, size_t num_fds)
+{
+	size_t size = sizeof(msg->header) + msg->header.size;
+	bool request_ack;
+	int rc;
+
+	msg->header.flags |= VHOST_USER_VERSION;
+
+	/*
+	 * The need_response flag indicates that we already need a response,
+	 * e.g. to read the features. In these cases, don't request an ACK as
+	 * it is meaningless. Also request an ACK only if supported.
+	 */
+	request_ack = !need_response;
+	if (!(vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK)))
+		request_ack = false;
+
+	if (request_ack)
+		msg->header.flags |= VHOST_USER_FLAG_NEED_REPLY;
+
+	rc = full_sendmsg_fds(vu_dev->sock, msg, size, fds, num_fds);
+	if (rc < 0)
+		return rc;
+
+	if (request_ack) {
+		uint64_t status;
+
+		rc = vhost_user_recv_u64(vu_dev, &status);
+		if (rc)
+			return rc;
+
+		if (status) {
+			vu_err(vu_dev, "slave reports error: %llu\n", status);
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static int vhost_user_send_no_payload(struct virtio_uml_device *vu_dev,
+				      bool need_response, u32 request)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+	};
+
+	return vhost_user_send(vu_dev, need_response, &msg, NULL, 0);
+}
+
+static int vhost_user_send_no_payload_fd(struct virtio_uml_device *vu_dev,
+					 u32 request, int fd)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, &fd, 1);
+}
+
+static int vhost_user_send_u64(struct virtio_uml_device *vu_dev,
+			       u32 request, u64 value)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.integer),
+		.payload.integer = value,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_owner(struct virtio_uml_device *vu_dev)
+{
+	return vhost_user_send_no_payload(vu_dev, false, VHOST_USER_SET_OWNER);
+}
+
+static int vhost_user_get_features(struct virtio_uml_device *vu_dev,
+				   u64 *features)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+					    VHOST_USER_GET_FEATURES);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, features);
+}
+
+static int vhost_user_set_features(struct virtio_uml_device *vu_dev,
+				   u64 features)
+{
+	return vhost_user_send_u64(vu_dev, VHOST_USER_SET_FEATURES, features);
+}
+
+static int vhost_user_get_protocol_features(struct virtio_uml_device *vu_dev,
+					    u64 *protocol_features)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+			VHOST_USER_GET_PROTOCOL_FEATURES);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, protocol_features);
+}
+
+static int vhost_user_set_protocol_features(struct virtio_uml_device *vu_dev,
+					    u64 protocol_features)
+{
+	return vhost_user_send_u64(vu_dev, VHOST_USER_SET_PROTOCOL_FEATURES,
+				   protocol_features);
+}
+
+static void vhost_user_reply(struct virtio_uml_device *vu_dev,
+			     struct vhost_user_msg *msg, int response)
+{
+	struct vhost_user_msg reply = {
+		.payload.integer = response,
+	};
+	size_t size = sizeof(reply.header) + sizeof(reply.payload.integer);
+	int rc;
+
+	reply.header = msg->header;
+	reply.header.flags &= ~VHOST_USER_FLAG_NEED_REPLY;
+	reply.header.flags |= VHOST_USER_FLAG_REPLY;
+	reply.header.size = sizeof(reply.payload.integer);
+
+	rc = full_sendmsg_fds(vu_dev->req_fd, &reply, size, NULL, 0);
+
+	if (rc)
+		vu_err(vu_dev,
+		       "sending reply to slave request failed: %d (size %zu)\n",
+		       rc, size);
+}
+
+static irqreturn_t vu_req_interrupt(int irq, void *data)
+{
+	struct virtio_uml_device *vu_dev = data;
+	int response = 1;
+	struct {
+		struct vhost_user_msg msg;
+		u8 extra_payload[512];
+	} msg;
+	int rc;
+
+	rc = vhost_user_recv_req(vu_dev, &msg.msg,
+				 sizeof(msg.msg.payload) +
+				 sizeof(msg.extra_payload));
+
+	if (rc)
+		return IRQ_NONE;
+
+	switch (msg.msg.header.request) {
+	case VHOST_USER_SLAVE_CONFIG_CHANGE_MSG:
+		virtio_config_changed(&vu_dev->vdev);
+		response = 0;
+		break;
+	case VHOST_USER_SLAVE_IOTLB_MSG:
+		/* not supported - VIRTIO_F_IOMMU_PLATFORM */
+	case VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG:
+		/* not supported - VHOST_USER_PROTOCOL_F_HOST_NOTIFIER */
+	default:
+		vu_err(vu_dev, "unexpected slave request %d\n",
+		       msg.msg.header.request);
+	}
+
+	if (msg.msg.header.flags & VHOST_USER_FLAG_NEED_REPLY)
+		vhost_user_reply(vu_dev, &msg.msg, response);
+
+	return IRQ_HANDLED;
+}
+
+static int vhost_user_init_slave_req(struct virtio_uml_device *vu_dev)
+{
+	int rc, req_fds[2];
+
+	/* Use a pipe for slave req fd, SIGIO is not supported for eventfd */
+	rc = os_pipe(req_fds, true, true);
+	if (rc < 0)
+		return rc;
+	vu_dev->req_fd = req_fds[0];
+
+	rc = um_request_irq(VIRTIO_IRQ, vu_dev->req_fd, IRQ_READ,
+			    vu_req_interrupt, IRQF_SHARED,
+			    vu_dev->pdev->name, vu_dev);
+	if (rc)
+		goto err_close;
+
+	rc = vhost_user_send_no_payload_fd(vu_dev, VHOST_USER_SET_SLAVE_REQ_FD,
+					   req_fds[1]);
+	if (rc)
+		goto err_free_irq;
+
+	goto out;
+
+err_free_irq:
+	um_free_irq(VIRTIO_IRQ, vu_dev);
+err_close:
+	os_close_file(req_fds[0]);
+out:
+	/* Close unused write end of request fds */
+	os_close_file(req_fds[1]);
+	return rc;
+}
+
+static int vhost_user_init(struct virtio_uml_device *vu_dev)
+{
+	int rc = vhost_user_set_owner(vu_dev);
+
+	if (rc)
+		return rc;
+	rc = vhost_user_get_features(vu_dev, &vu_dev->features);
+	if (rc)
+		return rc;
+
+	if (vu_dev->features & BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)) {
+		rc = vhost_user_get_protocol_features(vu_dev,
+				&vu_dev->protocol_features);
+		if (rc)
+			return rc;
+		vu_dev->protocol_features &= VHOST_USER_SUPPORTED_PROTOCOL_F;
+		rc = vhost_user_set_protocol_features(vu_dev,
+				vu_dev->protocol_features);
+		if (rc)
+			return rc;
+	}
+
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
+		rc = vhost_user_init_slave_req(vu_dev);
+		if (rc)
+			return rc;
+	}
+
+	return 0;
+}
+
+static void vhost_user_get_config(struct virtio_uml_device *vu_dev,
+				  u32 offset, void *buf, u32 len)
+{
+	u32 cfg_size = offset + len;
+	struct vhost_user_msg *msg;
+	size_t payload_size = sizeof(msg->payload.config) + cfg_size;
+	size_t msg_size = sizeof(msg->header) + payload_size;
+	int rc;
+
+	if (!(vu_dev->protocol_features &
+	      BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG)))
+		return;
+
+	msg = kzalloc(msg_size, GFP_KERNEL);
+	if (!msg)
+		return;
+	msg->header.request = VHOST_USER_GET_CONFIG;
+	msg->header.size = payload_size;
+	msg->payload.config.offset = 0;
+	msg->payload.config.size = cfg_size;
+
+	rc = vhost_user_send(vu_dev, true, msg, NULL, 0);
+	if (rc) {
+		vu_err(vu_dev, "sending VHOST_USER_GET_CONFIG failed: %d\n",
+		       rc);
+		goto free;
+	}
+
+	rc = vhost_user_recv_resp(vu_dev, msg, msg_size);
+	if (rc) {
+		vu_err(vu_dev,
+		       "receiving VHOST_USER_GET_CONFIG response failed: %d\n",
+		       rc);
+		goto free;
+	}
+
+	if (msg->header.size != payload_size ||
+	    msg->payload.config.size != cfg_size) {
+		rc = -EPROTO;
+		vu_err(vu_dev,
+		       "Invalid VHOST_USER_GET_CONFIG sizes (payload %d expected %zu, config %u expected %u)\n",
+		       msg->header.size, payload_size,
+		       msg->payload.config.size, cfg_size);
+		goto free;
+	}
+	memcpy(buf, msg->payload.config.payload + offset, len);
+
+free:
+	kfree(msg);
+}
+
+static void vhost_user_set_config(struct virtio_uml_device *vu_dev,
+				  u32 offset, const void *buf, u32 len)
+{
+	struct vhost_user_msg *msg;
+	size_t payload_size = sizeof(msg->payload.config) + len;
+	size_t msg_size = sizeof(msg->header) + payload_size;
+	int rc;
+
+	if (!(vu_dev->protocol_features &
+	      BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG)))
+		return;
+
+	msg = kzalloc(msg_size, GFP_KERNEL);
+	if (!msg)
+		return;
+	msg->header.request = VHOST_USER_SET_CONFIG;
+	msg->header.size = payload_size;
+	msg->payload.config.offset = offset;
+	msg->payload.config.size = len;
+	memcpy(msg->payload.config.payload, buf, len);
+
+	rc = vhost_user_send(vu_dev, false, msg, NULL, 0);
+	if (rc)
+		vu_err(vu_dev, "sending VHOST_USER_SET_CONFIG failed: %d\n",
+		       rc);
+
+	kfree(msg);
+}
+
+static int vhost_user_init_mem_region(u64 addr, u64 size, int *fd_out,
+				      struct vhost_user_mem_region *region_out)
+{
+	unsigned long long mem_offset;
+	int rc = phys_mapping(addr, &mem_offset);
+
+	if (WARN(rc < 0, "phys_mapping of 0x%llx returned %d\n", addr, rc))
+		return -EFAULT;
+	*fd_out = rc;
+	region_out->guest_addr = addr;
+	region_out->user_addr = addr;
+	region_out->size = size;
+	region_out->mmap_offset = mem_offset;
+
+	/* Ensure mapping is valid for the entire region */
+	rc = phys_mapping(addr + size - 1, &mem_offset);
+	if (WARN(rc != *fd_out, "phys_mapping of 0x%llx failed: %d != %d\n",
+		 addr + size - 1, rc, *fd_out))
+		return -EFAULT;
+	return 0;
+}
+
+static int vhost_user_set_mem_table(struct virtio_uml_device *vu_dev)
+{
+	struct vhost_user_msg msg = {
+		.header.request = VHOST_USER_SET_MEM_TABLE,
+		.header.size = sizeof(msg.payload.mem_regions),
+		.payload.mem_regions.num = 1,
+	};
+	unsigned long reserved = uml_reserved - uml_physmem;
+	int fds[2];
+	int rc;
+
+	/*
+	 * This is a bit tricky, see also the comment with setup_physmem().
+	 *
+	 * Essentially, setup_physmem() uses a file to mmap() our physmem,
+	 * but the code and data we *already* have is omitted. To us, this
+	 * is no difference, since they both become part of our address
+	 * space and memory consumption. To somebody looking in from the
+	 * outside, however, it is different because the part of our memory
+	 * consumption that's already part of the binary (code/data) is not
+	 * mapped from the file, so it's not visible to another mmap from
+	 * the file descriptor.
+	 *
+	 * Thus, don't advertise this space to the vhost-user slave. This
+	 * means that the slave will likely abort or similar when we give
+	 * it an address from the hidden range, since it's not marked as
+	 * a valid address, but at least that way we detect the issue and
+	 * don't just have the slave read an all-zeroes buffer from the
+	 * shared memory file, or write something there that we can never
+	 * see (depending on the direction of the virtqueue traffic.)
+	 *
+	 * Since we usually don't want to use .text for virtio buffers,
+	 * this effectively means that you cannot use
+	 *  1) global variables, which are in the .bss and not in the shm
+	 *     file-backed memory
+	 *  2) the stack in some processes, depending on where they have
+	 *     their stack (or maybe only no interrupt stack?)
+	 *
+	 * The stack is already not typically valid for DMA, so this isn't
+	 * much of a restriction, but global variables might be encountered.
+	 *
+	 * It might be possible to fix it by copying around the data that's
+	 * between bss_start and where we map the file now, but it's not
+	 * something that you typically encounter with virtio drivers, so
+	 * it didn't seem worthwhile.
+	 */
+	rc = vhost_user_init_mem_region(reserved, physmem_size - reserved,
+					&fds[0],
+					&msg.payload.mem_regions.regions[0]);
+
+	if (rc < 0)
+		return rc;
+	if (highmem) {
+		msg.payload.mem_regions.num++;
+		rc = vhost_user_init_mem_region(__pa(end_iomem), highmem,
+				&fds[1], &msg.payload.mem_regions.regions[1]);
+		if (rc < 0)
+			return rc;
+	}
+
+	return vhost_user_send(vu_dev, false, &msg, fds,
+			       msg.payload.mem_regions.num);
+}
+
+static int vhost_user_set_vring_state(struct virtio_uml_device *vu_dev,
+				      u32 request, u32 index, u32 num)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.vring_state),
+		.payload.vring_state.index = index,
+		.payload.vring_state.num = num,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_vring_num(struct virtio_uml_device *vu_dev,
+				    u32 index, u32 num)
+{
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_NUM,
+					  index, num);
+}
+
+static int vhost_user_set_vring_base(struct virtio_uml_device *vu_dev,
+				     u32 index, u32 offset)
+{
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_BASE,
+					  index, offset);
+}
+
+static int vhost_user_set_vring_addr(struct virtio_uml_device *vu_dev,
+				     u32 index, u64 desc, u64 used, u64 avail,
+				     u64 log)
+{
+	struct vhost_user_msg msg = {
+		.header.request = VHOST_USER_SET_VRING_ADDR,
+		.header.size = sizeof(msg.payload.vring_addr),
+		.payload.vring_addr.index = index,
+		.payload.vring_addr.desc = desc,
+		.payload.vring_addr.used = used,
+		.payload.vring_addr.avail = avail,
+		.payload.vring_addr.log = log,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_vring_fd(struct virtio_uml_device *vu_dev,
+				   u32 request, int index, int fd)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.integer),
+		.payload.integer = index,
+	};
+
+	if (index & ~VHOST_USER_VRING_INDEX_MASK)
+		return -EINVAL;
+	if (fd < 0) {
+		msg.payload.integer |= VHOST_USER_VRING_POLL_MASK;
+		return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+	}
+	return vhost_user_send(vu_dev, false, &msg, &fd, 1);
+}
+
+static int vhost_user_set_vring_call(struct virtio_uml_device *vu_dev,
+				     int index, int fd)
+{
+	return vhost_user_set_vring_fd(vu_dev, VHOST_USER_SET_VRING_CALL,
+				       index, fd);
+}
+
+static int vhost_user_set_vring_kick(struct virtio_uml_device *vu_dev,
+				     int index, int fd)
+{
+	return vhost_user_set_vring_fd(vu_dev, VHOST_USER_SET_VRING_KICK,
+				       index, fd);
+}
+
+static int vhost_user_set_vring_enable(struct virtio_uml_device *vu_dev,
+				       u32 index, bool enable)
+{
+	if (!(vu_dev->features & BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)))
+		return 0;
+
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_ENABLE,
+					  index, enable);
+}
+
+
+/* Virtio interface */
+
+static bool vu_notify(struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+	const uint64_t n = 1;
+	int rc;
+
+	do {
+		rc = os_write_file(info->kick_fd, &n, sizeof(n));
+	} while (rc == -EINTR);
+	return !WARN(rc != sizeof(n), "write returned %d\n", rc);
+}
+
+static irqreturn_t vu_interrupt(int irq, void *opaque)
+{
+	struct virtqueue *vq = opaque;
+	struct virtio_uml_vq_info *info = vq->priv;
+	uint64_t n;
+	int rc;
+	irqreturn_t ret = IRQ_NONE;
+
+	do {
+		rc = os_read_file(info->call_fd, &n, sizeof(n));
+		if (rc == sizeof(n))
+			ret |= vring_interrupt(irq, vq);
+	} while (rc == sizeof(n) || rc == -EINTR);
+	WARN(rc != -EAGAIN, "read returned %d\n", rc);
+	return ret;
+}
+
+
+static void vu_get(struct virtio_device *vdev, unsigned offset,
+		   void *buf, unsigned len)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vhost_user_get_config(vu_dev, offset, buf, len);
+}
+
+static void vu_set(struct virtio_device *vdev, unsigned offset,
+		   const void *buf, unsigned len)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vhost_user_set_config(vu_dev, offset, buf, len);
+}
+
+static u8 vu_get_status(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->status;
+}
+
+static void vu_set_status(struct virtio_device *vdev, u8 status)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vu_dev->status = status;
+}
+
+static void vu_reset(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vu_dev->status = 0;
+}
+
+static void vu_del_vq(struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+
+	um_free_irq(VIRTIO_IRQ, vq);
+
+	os_close_file(info->call_fd);
+	os_close_file(info->kick_fd);
+
+	vring_del_virtqueue(vq);
+	kfree(info);
+}
+
+static void vu_del_vqs(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	struct virtqueue *vq, *n;
+	u64 features;
+
+	/* Note: reverse order as a workaround to a decoding bug in snabb */
+	list_for_each_entry_reverse(vq, &vdev->vqs, list)
+		WARN_ON(vhost_user_set_vring_enable(vu_dev, vq->index, false));
+
+	/* Ensure previous messages have been processed */
+	WARN_ON(vhost_user_get_features(vu_dev, &features));
+
+	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
+		vu_del_vq(vq);
+}
+
+static int vu_setup_vq_call_fd(struct virtio_uml_device *vu_dev,
+			       struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+	int call_fds[2];
+	int rc;
+
+	/* Use a pipe for call fd, since SIGIO is not supported for eventfd */
+	rc = os_pipe(call_fds, true, true);
+	if (rc < 0)
+		return rc;
+
+	info->call_fd = call_fds[0];
+	rc = um_request_irq(VIRTIO_IRQ, info->call_fd, IRQ_READ,
+			    vu_interrupt, IRQF_SHARED, info->name, vq);
+	if (rc)
+		goto close_both;
+
+	rc = vhost_user_set_vring_call(vu_dev, vq->index, call_fds[1]);
+	if (rc)
+		goto release_irq;
+
+	goto out;
+
+release_irq:
+	um_free_irq(VIRTIO_IRQ, vq);
+close_both:
+	os_close_file(call_fds[0]);
+out:
+	/* Close (unused) write end of call fds */
+	os_close_file(call_fds[1]);
+
+	return rc;
+}
+
+static struct virtqueue *vu_setup_vq(struct virtio_device *vdev,
+				     unsigned index, vq_callback_t *callback,
+				     const char *name, bool ctx)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	struct platform_device *pdev = vu_dev->pdev;
+	struct virtio_uml_vq_info *info;
+	struct virtqueue *vq;
+	int num = MAX_SUPPORTED_QUEUE_SIZE;
+	int rc;
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		rc = -ENOMEM;
+		goto error_kzalloc;
+	}
+	snprintf(info->name, sizeof(info->name), "%s.%d-%s", pdev->name,
+		 pdev->id, name);
+
+	vq = vring_create_virtqueue(index, num, PAGE_SIZE, vdev, true, true,
+				    ctx, vu_notify, callback, info->name);
+	if (!vq) {
+		rc = -ENOMEM;
+		goto error_create;
+	}
+	vq->priv = info;
+	num = virtqueue_get_vring_size(vq);
+
+	rc = os_eventfd(0, 0);
+	if (rc < 0)
+		goto error_kick;
+	info->kick_fd = rc;
+
+	rc = vu_setup_vq_call_fd(vu_dev, vq);
+	if (rc)
+		goto error_call;
+
+	rc = vhost_user_set_vring_num(vu_dev, index, num);
+	if (rc)
+		goto error_setup;
+
+	rc = vhost_user_set_vring_base(vu_dev, index, 0);
+	if (rc)
+		goto error_setup;
+
+	rc = vhost_user_set_vring_addr(vu_dev, index,
+				       virtqueue_get_desc_addr(vq),
+				       virtqueue_get_used_addr(vq),
+				       virtqueue_get_avail_addr(vq),
+				       (u64) -1);
+	if (rc)
+		goto error_setup;
+
+	return vq;
+
+error_setup:
+	um_free_irq(VIRTIO_IRQ, vq);
+	os_close_file(info->call_fd);
+error_call:
+	os_close_file(info->kick_fd);
+error_kick:
+	vring_del_virtqueue(vq);
+error_create:
+	kfree(info);
+error_kzalloc:
+	return ERR_PTR(rc);
+}
+
+static int vu_find_vqs(struct virtio_device *vdev, unsigned nvqs,
+		       struct virtqueue *vqs[], vq_callback_t *callbacks[],
+		       const char * const names[], const bool *ctx,
+		       struct irq_affinity *desc)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	int i, queue_idx = 0, rc;
+	struct virtqueue *vq;
+
+	rc = vhost_user_set_mem_table(vu_dev);
+	if (rc)
+		return rc;
+
+	for (i = 0; i < nvqs; ++i) {
+		if (!names[i]) {
+			vqs[i] = NULL;
+			continue;
+		}
+
+		vqs[i] = vu_setup_vq(vdev, queue_idx++, callbacks[i], names[i],
+				     ctx ? ctx[i] : false);
+		if (IS_ERR(vqs[i])) {
+			rc = PTR_ERR(vqs[i]);
+			goto error_setup;
+		}
+	}
+
+	list_for_each_entry(vq, &vdev->vqs, list) {
+		struct virtio_uml_vq_info *info = vq->priv;
+
+		rc = vhost_user_set_vring_kick(vu_dev, vq->index,
+					       info->kick_fd);
+		if (rc)
+			goto error_setup;
+
+		rc = vhost_user_set_vring_enable(vu_dev, vq->index, true);
+		if (rc)
+			goto error_setup;
+	}
+
+	return 0;
+
+error_setup:
+	vu_del_vqs(vdev);
+	return rc;
+}
+
+static u64 vu_get_features(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->features;
+}
+
+static int vu_finalize_features(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	u64 supported = vdev->features & VHOST_USER_SUPPORTED_F;
+
+	vring_transport_features(vdev);
+	vu_dev->features = vdev->features | supported;
+
+	return vhost_user_set_features(vu_dev, vu_dev->features);
+}
+
+static const char *vu_bus_name(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->pdev->name;
+}
+
+static const struct virtio_config_ops virtio_uml_config_ops = {
+	.get = vu_get,
+	.set = vu_set,
+	.get_status = vu_get_status,
+	.set_status = vu_set_status,
+	.reset = vu_reset,
+	.find_vqs = vu_find_vqs,
+	.del_vqs = vu_del_vqs,
+	.get_features = vu_get_features,
+	.finalize_features = vu_finalize_features,
+	.bus_name = vu_bus_name,
+};
+
+static void virtio_uml_release_dev(struct device *d)
+{
+	struct virtio_device *vdev =
+			container_of(d, struct virtio_device, dev);
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	/* might not have been opened due to not negotiating the feature */
+	if (vu_dev->req_fd >= 0) {
+		um_free_irq(VIRTIO_IRQ, vu_dev);
+		os_close_file(vu_dev->req_fd);
+	}
+
+	os_close_file(vu_dev->sock);
+}
+
+/* Platform device */
+
+struct virtio_uml_platform_data {
+	u32 virtio_device_id;
+	const char *socket_path;
+};
+
+static int virtio_uml_probe(struct platform_device *pdev)
+{
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+	struct virtio_uml_device *vu_dev;
+	int rc;
+
+	if (!pdata)
+		return -EINVAL;
+
+	vu_dev = devm_kzalloc(&pdev->dev, sizeof(*vu_dev), GFP_KERNEL);
+	if (!vu_dev)
+		return -ENOMEM;
+
+	vu_dev->vdev.dev.parent = &pdev->dev;
+	vu_dev->vdev.dev.release = virtio_uml_release_dev;
+	vu_dev->vdev.config = &virtio_uml_config_ops;
+	vu_dev->vdev.id.device = pdata->virtio_device_id;
+	vu_dev->vdev.id.vendor = VIRTIO_DEV_ANY_ID;
+	vu_dev->pdev = pdev;
+	vu_dev->req_fd = -1;
+
+	do {
+		rc = os_connect_socket(pdata->socket_path);
+	} while (rc == -EINTR);
+	if (rc < 0)
+		return rc;
+	vu_dev->sock = rc;
+
+	rc = vhost_user_init(vu_dev);
+	if (rc)
+		goto error_init;
+
+	platform_set_drvdata(pdev, vu_dev);
+
+	rc = register_virtio_device(&vu_dev->vdev);
+	if (rc)
+		put_device(&vu_dev->vdev.dev);
+	return rc;
+
+error_init:
+	os_close_file(vu_dev->sock);
+	return rc;
+}
+
+static int virtio_uml_remove(struct platform_device *pdev)
+{
+	struct virtio_uml_device *vu_dev = platform_get_drvdata(pdev);
+
+	unregister_virtio_device(&vu_dev->vdev);
+	return 0;
+}
+
+/* Command line device list */
+
+static void vu_cmdline_release_dev(struct device *d)
+{
+}
+
+static struct device vu_cmdline_parent = {
+	.init_name = "virtio-uml-cmdline",
+	.release = vu_cmdline_release_dev,
+};
+
+static bool vu_cmdline_parent_registered;
+static int vu_cmdline_id;
+
+static int vu_cmdline_set(const char *device, const struct kernel_param *kp)
+{
+	const char *ids = strchr(device, ':');
+	unsigned int virtio_device_id;
+	int processed, consumed, err;
+	char *socket_path;
+	struct virtio_uml_platform_data pdata;
+	struct platform_device *pdev;
+
+	if (!ids || ids == device)
+		return -EINVAL;
+
+	processed = sscanf(ids, ":%u%n:%d%n",
+			   &virtio_device_id, &consumed,
+			   &vu_cmdline_id, &consumed);
+
+	if (processed < 1 || ids[consumed])
+		return -EINVAL;
+
+	if (!vu_cmdline_parent_registered) {
+		err = device_register(&vu_cmdline_parent);
+		if (err) {
+			pr_err("Failed to register parent device!\n");
+			put_device(&vu_cmdline_parent);
+			return err;
+		}
+		vu_cmdline_parent_registered = true;
+	}
+
+	socket_path = kmemdup_nul(device, ids - device, GFP_KERNEL);
+	if (!socket_path)
+		return -ENOMEM;
+
+	pdata.virtio_device_id = (u32) virtio_device_id;
+	pdata.socket_path = socket_path;
+
+	pr_info("Registering device virtio-uml.%d id=%d at %s\n",
+		vu_cmdline_id, virtio_device_id, socket_path);
+
+	pdev = platform_device_register_data(&vu_cmdline_parent, "virtio-uml",
+					     vu_cmdline_id++, &pdata,
+					     sizeof(pdata));
+	err = PTR_ERR_OR_ZERO(pdev);
+	if (err)
+		goto free;
+	return 0;
+
+free:
+	kfree(socket_path);
+	return err;
+}
+
+static int vu_cmdline_get_device(struct device *dev, void *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+	char *buffer = data;
+	unsigned int len = strlen(buffer);
+
+	snprintf(buffer + len, PAGE_SIZE - len, "%s:%d:%d\n",
+		 pdata->socket_path, pdata->virtio_device_id, pdev->id);
+	return 0;
+}
+
+static int vu_cmdline_get(char *buffer, const struct kernel_param *kp)
+{
+	buffer[0] = '\0';
+	if (vu_cmdline_parent_registered)
+		device_for_each_child(&vu_cmdline_parent, buffer,
+				      vu_cmdline_get_device);
+	return strlen(buffer) + 1;
+}
+
+static const struct kernel_param_ops vu_cmdline_param_ops = {
+	.set = vu_cmdline_set,
+	.get = vu_cmdline_get,
+};
+
+device_param_cb(device, &vu_cmdline_param_ops, NULL, S_IRUSR);
+__uml_help(vu_cmdline_param_ops,
+"virtio_uml.device=<socket>:<virtio_id>[:<platform_id>]\n"
+"    Configure a virtio device over a vhost-user socket.\n"
+"    See virtio_ids.h for a list of possible virtio device id values.\n"
+"    Optionally use a specific platform_device id.\n\n"
+);
+
+
+static int vu_unregister_cmdline_device(struct device *dev, void *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+
+	kfree(pdata->socket_path);
+	platform_device_unregister(pdev);
+	return 0;
+}
+
+static void vu_unregister_cmdline_devices(void)
+{
+	if (vu_cmdline_parent_registered) {
+		device_for_each_child(&vu_cmdline_parent, NULL,
+				      vu_unregister_cmdline_device);
+		device_unregister(&vu_cmdline_parent);
+		vu_cmdline_parent_registered = false;
+	}
+}
+
+/* Platform driver */
+
+static const struct of_device_id virtio_uml_match[] = {
+	{ .compatible = "virtio,uml", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, virtio_uml_match);
+
+static struct platform_driver virtio_uml_driver = {
+	.probe = virtio_uml_probe,
+	.remove = virtio_uml_remove,
+	.driver = {
+		.name = "virtio-uml",
+		.of_match_table = virtio_uml_match,
+	},
+};
+
+static int __init virtio_uml_init(void)
+{
+	return platform_driver_register(&virtio_uml_driver);
+}
+
+static void __exit virtio_uml_exit(void)
+{
+	platform_driver_unregister(&virtio_uml_driver);
+	vu_unregister_cmdline_devices();
+}
+
+module_init(virtio_uml_init);
+module_exit(virtio_uml_exit);
+__uml_exitcall(virtio_uml_exit);
+
+MODULE_DESCRIPTION("UML driver for vhost-user virtio devices");
+MODULE_LICENSE("GPL");
diff --git a/arch/um/drivers/xterm.c b/arch/um/drivers/xterm.c
index 20e30be..fc7f1e7 100644
--- a/arch/um/drivers/xterm.c
+++ b/arch/um/drivers/xterm.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stddef.h>
diff --git a/arch/um/drivers/xterm.h b/arch/um/drivers/xterm.h
index 56b9c4a..5968da3 100644
--- a/arch/um/drivers/xterm.h
+++ b/arch/um/drivers/xterm.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __XTERM_H__
diff --git a/arch/um/drivers/xterm_kern.c b/arch/um/drivers/xterm_kern.c
index e8f9957..d64ef6d 100644
--- a/arch/um/drivers/xterm_kern.c
+++ b/arch/um/drivers/xterm_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/slab.h>
diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
index b10dde6..398006d 100644
--- a/arch/um/include/asm/Kbuild
+++ b/arch/um/include/asm/Kbuild
@@ -1,4 +1,4 @@
-generic-y += barrier.h
+# SPDX-License-Identifier: GPL-2.0
 generic-y += bpf_perf_event.h
 generic-y += bug.h
 generic-y += compat.h
@@ -10,14 +10,13 @@
 generic-y += extable.h
 generic-y += ftrace.h
 generic-y += futex.h
-generic-y += hardirq.h
 generic-y += hw_irq.h
-generic-y += io.h
 generic-y += irq_regs.h
 generic-y += irq_work.h
 generic-y += kdebug.h
 generic-y += mcs_spinlock.h
 generic-y += mm-arch-hooks.h
+generic-y += mmiowb.h
 generic-y += param.h
 generic-y += pci.h
 generic-y += percpu.h
diff --git a/arch/um/include/asm/a.out-core.h b/arch/um/include/asm/a.out-core.h
deleted file mode 100644
index 995643b..0000000
--- a/arch/um/include/asm/a.out-core.h
+++ /dev/null
@@ -1,27 +0,0 @@
-/* a.out coredump register dumper
- *
- * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public Licence
- * as published by the Free Software Foundation; either version
- * 2 of the Licence, or (at your option) any later version.
- */
-
-#ifndef __UM_A_OUT_CORE_H
-#define __UM_A_OUT_CORE_H
-
-#ifdef __KERNEL__
-
-#include <linux/user.h>
-
-/*
- * fill in the user structure for an a.out core dump
- */
-static inline void aout_dump_thread(struct pt_regs *regs, struct user *u)
-{
-}
-
-#endif /* __KERNEL__ */
-#endif /* __UM_A_OUT_CORE_H */
diff --git a/arch/um/include/asm/common.lds.S b/arch/um/include/asm/common.lds.S
index 7adb4e6..d7086b9 100644
--- a/arch/um/include/asm/common.lds.S
+++ b/arch/um/include/asm/common.lds.S
@@ -53,8 +53,6 @@
 	CON_INITCALL
   }
 
-  SECURITY_INIT
-
   .exitcall : {
 	__exitcall_begin = .;
 	*(.exitcall.exit)
@@ -85,8 +83,8 @@
 	__preinit_array_end = .;
   }
   .init_array : {
+        /* dummy - we call this ourselves */
 	__init_array_start = .;
-	*(.init_array)
 	__init_array_end = .;
   }
   .fini_array : {
diff --git a/arch/um/include/asm/irq.h b/arch/um/include/asm/irq.h
index 49ed3e3..42c6205 100644
--- a/arch/um/include/asm/irq.h
+++ b/arch/um/include/asm/irq.h
@@ -17,17 +17,18 @@
 #define TELNETD_IRQ 		12
 #define XTERM_IRQ 		13
 #define RANDOM_IRQ 		14
+#define VIRTIO_IRQ		15
 
 #ifdef CONFIG_UML_NET_VECTOR
 
-#define VECTOR_BASE_IRQ		15
+#define VECTOR_BASE_IRQ		(VIRTIO_IRQ + 1)
 #define VECTOR_IRQ_SPACE	8
 
-#define LAST_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ)
+#define LAST_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ - 1)
 
 #else
 
-#define LAST_IRQ RANDOM_IRQ
+#define LAST_IRQ VIRTIO_IRQ
 
 #endif
 
diff --git a/arch/um/include/asm/irqflags.h b/arch/um/include/asm/irqflags.h
index cbc6c00..0642ad9 100644
--- a/arch/um/include/asm/irqflags.h
+++ b/arch/um/include/asm/irqflags.h
@@ -32,7 +32,6 @@
 }
 
 #define ARCH_IRQ_DISABLED	0
-#define ARCh_IRQ_ENABLED	(SIGIO|SIGVTALRM)
 
 #include <asm-generic/irqflags.h>
 
diff --git a/arch/um/include/asm/kmap_types.h b/arch/um/include/asm/kmap_types.h
index 2e0a6b1..b0bd12d 100644
--- a/arch/um/include/asm/kmap_types.h
+++ b/arch/um/include/asm/kmap_types.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_KMAP_TYPES_H
diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h
index da70544..5b072ab 100644
--- a/arch/um/include/asm/mmu.h
+++ b/arch/um/include/asm/mmu.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __ARCH_UM_MMU_H
diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
index fca34b2..5aee062 100644
--- a/arch/um/include/asm/mmu_context.h
+++ b/arch/um/include/asm/mmu_context.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_MMU_CONTEXT_H
@@ -22,7 +22,6 @@
 }
 extern void arch_exit_mmap(struct mm_struct *mm);
 static inline void arch_unmap(struct mm_struct *mm,
-			struct vm_area_struct *vma,
 			unsigned long start, unsigned long end)
 {
 }
@@ -53,7 +52,7 @@
 	 * when the new ->mm is used for the first time.
 	 */
 	__switch_mm(&new->context.id);
-	down_write(&new->mmap_sem);
+	down_write_nested(&new->mmap_sem, 1);
 	uml_setup_stubs(new);
 	up_write(&new->mmap_sem);
 }
diff --git a/arch/um/include/asm/page.h b/arch/um/include/asm/page.h
index f878bec..95af12e 100644
--- a/arch/um/include/asm/page.h
+++ b/arch/um/include/asm/page.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2000 - 2003 Jeff Dike (jdike@addtoit.com)
  * Copyright 2003 PathScale, Inc.
- * Licensed under the GPL
  */
 
 #ifndef __UM_PAGE_H
diff --git a/arch/um/include/asm/pgalloc.h b/arch/um/include/asm/pgalloc.h
index bf90b2a..881e76d 100644
--- a/arch/um/include/asm/pgalloc.h
+++ b/arch/um/include/asm/pgalloc.h
@@ -1,8 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
  * Copyright 2003 PathScale, Inc.
  * Derived from include/asm-i386/pgalloc.h and include/asm-i386/pgtable.h
- * Licensed under the GPL
  */
 
 #ifndef __UM_PGALLOC_H
@@ -10,6 +10,8 @@
 
 #include <linux/mm.h>
 
+#include <asm-generic/pgalloc.h>	/* for pte_{alloc,free}_one */
+
 #define pmd_populate_kernel(mm, pmd, pte) \
 	set_pmd(pmd, __pmd(_PAGE_TABLE + (unsigned long) __pa(pte)))
 
@@ -25,23 +27,9 @@
 extern pgd_t *pgd_alloc(struct mm_struct *);
 extern void pgd_free(struct mm_struct *mm, pgd_t *pgd);
 
-extern pte_t *pte_alloc_one_kernel(struct mm_struct *, unsigned long);
-extern pgtable_t pte_alloc_one(struct mm_struct *, unsigned long);
-
-static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte)
-{
-	free_page((unsigned long) pte);
-}
-
-static inline void pte_free(struct mm_struct *mm, pgtable_t pte)
-{
-	pgtable_page_dtor(pte);
-	__free_page(pte);
-}
-
 #define __pte_free_tlb(tlb,pte, address)		\
 do {							\
-	pgtable_page_dtor(pte);				\
+	pgtable_pte_page_dtor(pte);			\
 	tlb_remove_page((tlb),(pte));			\
 } while (0)
 
@@ -55,7 +43,5 @@
 #define __pmd_free_tlb(tlb,x, address)   tlb_remove_page((tlb),virt_to_page(x))
 #endif
 
-#define check_pgt_cache()	do { } while (0)
-
 #endif
 
diff --git a/arch/um/include/asm/pgtable-2level.h b/arch/um/include/asm/pgtable-2level.h
index 179c0ea..32b3d26 100644
--- a/arch/um/include/asm/pgtable-2level.h
+++ b/arch/um/include/asm/pgtable-2level.h
@@ -1,8 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
  * Copyright 2003 PathScale, Inc.
  * Derived from include/asm-i386/pgtable.h
- * Licensed under the GPL
  */
 
 #ifndef __UM_PGTABLE_2LEVEL_H
diff --git a/arch/um/include/asm/pgtable-3level.h b/arch/um/include/asm/pgtable-3level.h
index c4d876d..9812269 100644
--- a/arch/um/include/asm/pgtable-3level.h
+++ b/arch/um/include/asm/pgtable-3level.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright 2003 PathScale Inc
  * Derived from include/asm-i386/pgtable.h
- * Licensed under the GPL
  */
 
 #ifndef __UM_PGTABLE_3LEVEL_H
diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
index 7485398..36a44d5 100644
--- a/arch/um/include/asm/pgtable.h
+++ b/arch/um/include/asm/pgtable.h
@@ -1,8 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright 2003 PathScale, Inc.
  * Derived from include/asm-i386/pgtable.h
- * Licensed under the GPL
  */
 
 #ifndef __UM_PGTABLE_H
@@ -32,8 +32,6 @@
 /* zero page used for uninitialized stuff */
 extern unsigned long *empty_zero_page;
 
-#define pgtable_cache_init() do ; while (0)
-
 /* Just any arbitrary offset to the start of the vmalloc VM area: the
  * current 8MB value just means that there will be a 8MB "hole" after the
  * physical memory until the kernel virtual memory starts.  That means that
@@ -197,12 +195,17 @@
 
 static inline pte_t pte_wrprotect(pte_t pte)
 { 
-	pte_clear_bits(pte, _PAGE_RW);
+	if (likely(pte_get_bits(pte, _PAGE_RW)))
+		pte_clear_bits(pte, _PAGE_RW);
+	else
+		return pte;
 	return(pte_mknewprot(pte)); 
 }
 
 static inline pte_t pte_mkread(pte_t pte)
 { 
+	if (unlikely(pte_get_bits(pte, _PAGE_USER)))
+		return pte;
 	pte_set_bits(pte, _PAGE_USER);
 	return(pte_mknewprot(pte)); 
 }
@@ -221,6 +224,8 @@
 
 static inline pte_t pte_mkwrite(pte_t pte)	
 {
+	if (unlikely(pte_get_bits(pte,  _PAGE_RW)))
+		return pte;
 	pte_set_bits(pte, _PAGE_RW);
 	return(pte_mknewprot(pte)); 
 }
@@ -256,7 +261,12 @@
 	*pteptr = pte_mknewpage(*pteptr);
 	if(pte_present(*pteptr)) *pteptr = pte_mknewprot(*pteptr);
 }
-#define set_pte_at(mm,addr,ptep,pteval) set_pte(ptep,pteval)
+
+static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
+			      pte_t *pteptr, pte_t pteval)
+{
+	set_pte(pteptr, pteval);
+}
 
 #define __HAVE_ARCH_PTE_SAME
 static inline int pte_same(pte_t pte_a, pte_t pte_b)
diff --git a/arch/um/include/asm/processor-generic.h b/arch/um/include/asm/processor-generic.h
index b58b746..afd9b26 100644
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_PROCESSOR_GENERIC_H
diff --git a/arch/um/include/asm/ptrace-generic.h b/arch/um/include/asm/ptrace-generic.h
index 5ab2062..81c647e 100644
--- a/arch/um/include/asm/ptrace-generic.h
+++ b/arch/um/include/asm/ptrace-generic.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_PTRACE_GENERIC_H
diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
index 9fb9cf8..2984feb 100644
--- a/arch/um/include/asm/syscall-generic.h
+++ b/arch/um/include/asm/syscall-generic.h
@@ -1,13 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * Access to user system call parameters and results
  *
  * See asm-generic/syscall.h for function descriptions.
  *
  * Copyright (C) 2015 Mickaël Salaün <mic@digikod.net>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #ifndef __UM_SYSCALL_GENERIC_H
@@ -53,84 +50,30 @@
 
 static inline void syscall_get_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
-					 unsigned int i, unsigned int n,
 					 unsigned long *args)
 {
 	const struct uml_pt_regs *r = &regs->regs;
 
-	switch (i) {
-	case 0:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG1(r);
-	case 1:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG2(r);
-	case 2:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG3(r);
-	case 3:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG4(r);
-	case 4:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG5(r);
-	case 5:
-		if (!n--)
-			break;
-		*args++ = UPT_SYSCALL_ARG6(r);
-	case 6:
-		if (!n--)
-			break;
-	default:
-		BUG();
-		break;
-	}
+	*args++ = UPT_SYSCALL_ARG1(r);
+	*args++ = UPT_SYSCALL_ARG2(r);
+	*args++ = UPT_SYSCALL_ARG3(r);
+	*args++ = UPT_SYSCALL_ARG4(r);
+	*args++ = UPT_SYSCALL_ARG5(r);
+	*args   = UPT_SYSCALL_ARG6(r);
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
-					 unsigned int i, unsigned int n,
 					 const unsigned long *args)
 {
 	struct uml_pt_regs *r = &regs->regs;
 
-	switch (i) {
-	case 0:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG1(r) = *args++;
-	case 1:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG2(r) = *args++;
-	case 2:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG3(r) = *args++;
-	case 3:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG4(r) = *args++;
-	case 4:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG5(r) = *args++;
-	case 5:
-		if (!n--)
-			break;
-		UPT_SYSCALL_ARG6(r) = *args++;
-	case 6:
-		if (!n--)
-			break;
-	default:
-		BUG();
-		break;
-	}
+	UPT_SYSCALL_ARG1(r) = *args++;
+	UPT_SYSCALL_ARG2(r) = *args++;
+	UPT_SYSCALL_ARG3(r) = *args++;
+	UPT_SYSCALL_ARG4(r) = *args++;
+	UPT_SYSCALL_ARG5(r) = *args++;
+	UPT_SYSCALL_ARG6(r) = *args;
 }
 
 /* See arch/x86/um/asm/syscall.h for syscall_get_arch() definition. */
diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
index 4eecd96..4c19ce4 100644
--- a/arch/um/include/asm/thread_info.h
+++ b/arch/um/include/asm/thread_info.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_THREAD_INFO_H
diff --git a/arch/um/include/asm/tlb.h b/arch/um/include/asm/tlb.h
index dce6db1..70ee603 100644
--- a/arch/um/include/asm/tlb.h
+++ b/arch/um/include/asm/tlb.h
@@ -2,162 +2,8 @@
 #ifndef __UM_TLB_H
 #define __UM_TLB_H
 
-#include <linux/pagemap.h>
-#include <linux/swap.h>
-#include <asm/percpu.h>
-#include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
-
-#define tlb_start_vma(tlb, vma) do { } while (0)
-#define tlb_end_vma(tlb, vma) do { } while (0)
-#define tlb_flush(tlb) flush_tlb_mm((tlb)->mm)
-
-/* struct mmu_gather is an opaque type used by the mm code for passing around
- * any data needed by arch specific code for tlb_remove_page.
- */
-struct mmu_gather {
-	struct mm_struct	*mm;
-	unsigned int		need_flush; /* Really unmapped some ptes? */
-	unsigned long		start;
-	unsigned long		end;
-	unsigned int		fullmm; /* non-zero means full mm flush */
-};
-
-static inline void __tlb_remove_tlb_entry(struct mmu_gather *tlb, pte_t *ptep,
-					  unsigned long address)
-{
-	if (tlb->start > address)
-		tlb->start = address;
-	if (tlb->end < address + PAGE_SIZE)
-		tlb->end = address + PAGE_SIZE;
-}
-
-static inline void init_tlb_gather(struct mmu_gather *tlb)
-{
-	tlb->need_flush = 0;
-
-	tlb->start = TASK_SIZE;
-	tlb->end = 0;
-
-	if (tlb->fullmm) {
-		tlb->start = 0;
-		tlb->end = TASK_SIZE;
-	}
-}
-
-static inline void
-arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
-		unsigned long start, unsigned long end)
-{
-	tlb->mm = mm;
-	tlb->start = start;
-	tlb->end = end;
-	tlb->fullmm = !(start | (end+1));
-
-	init_tlb_gather(tlb);
-}
-
-extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
-			       unsigned long end);
-
-static inline void
-tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
-{
-	flush_tlb_mm_range(tlb->mm, tlb->start, tlb->end);
-}
-
-static inline void
-tlb_flush_mmu_free(struct mmu_gather *tlb)
-{
-	init_tlb_gather(tlb);
-}
-
-static inline void
-tlb_flush_mmu(struct mmu_gather *tlb)
-{
-	if (!tlb->need_flush)
-		return;
-
-	tlb_flush_mmu_tlbonly(tlb);
-	tlb_flush_mmu_free(tlb);
-}
-
-/* arch_tlb_finish_mmu
- *	Called at the end of the shootdown operation to free up any resources
- *	that were required.
- */
-static inline void
-arch_tlb_finish_mmu(struct mmu_gather *tlb,
-		unsigned long start, unsigned long end, bool force)
-{
-	if (force) {
-		tlb->start = start;
-		tlb->end = end;
-		tlb->need_flush = 1;
-	}
-	tlb_flush_mmu(tlb);
-
-	/* keep the page table cache within bounds */
-	check_pgt_cache();
-}
-
-/* tlb_remove_page
- *	Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)),
- *	while handling the additional races in SMP caused by other CPUs
- *	caching valid mappings in their TLBs.
- */
-static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
-{
-	tlb->need_flush = 1;
-	free_page_and_swap_cache(page);
-	return false; /* avoid calling tlb_flush_mmu */
-}
-
-static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
-{
-	__tlb_remove_page(tlb, page);
-}
-
-static inline bool __tlb_remove_page_size(struct mmu_gather *tlb,
-					  struct page *page, int page_size)
-{
-	return __tlb_remove_page(tlb, page);
-}
-
-static inline void tlb_remove_page_size(struct mmu_gather *tlb,
-					struct page *page, int page_size)
-{
-	return tlb_remove_page(tlb, page);
-}
-
-/**
- * tlb_remove_tlb_entry - remember a pte unmapping for later tlb invalidation.
- *
- * Record the fact that pte's were really umapped in ->need_flush, so we can
- * later optimise away the tlb invalidate.   This helps when userspace is
- * unmapping already-unmapped pages, which happens quite a lot.
- */
-#define tlb_remove_tlb_entry(tlb, ptep, address)		\
-	do {							\
-		tlb->need_flush = 1;				\
-		__tlb_remove_tlb_entry(tlb, ptep, address);	\
-	} while (0)
-
-#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address)	\
-	tlb_remove_tlb_entry(tlb, ptep, address)
-
-#define tlb_remove_check_page_size_change tlb_remove_check_page_size_change
-static inline void tlb_remove_check_page_size_change(struct mmu_gather *tlb,
-						     unsigned int page_size)
-{
-}
-
-#define pte_free_tlb(tlb, ptep, addr) __pte_free_tlb(tlb, ptep, addr)
-
-#define pud_free_tlb(tlb, pudp, addr) __pud_free_tlb(tlb, pudp, addr)
-
-#define pmd_free_tlb(tlb, pmdp, addr) __pmd_free_tlb(tlb, pmdp, addr)
-
-#define tlb_migrate_finish(mm) do {} while (0)
+#include <asm-generic/cacheflush.h>
+#include <asm-generic/tlb.h>
 
 #endif
diff --git a/arch/um/include/asm/tlbflush.h b/arch/um/include/asm/tlbflush.h
index 614f2c0..a5bda89 100644
--- a/arch/um/include/asm/tlbflush.h
+++ b/arch/um/include/asm/tlbflush.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_TLBFLUSH_H
diff --git a/arch/um/include/asm/uaccess.h b/arch/um/include/asm/uaccess.h
index cc00fc5..fe66d65 100644
--- a/arch/um/include/asm/uaccess.h
+++ b/arch/um/include/asm/uaccess.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
  * Copyright (C) 2015 Richard Weinberger (richard@nod.at)
- * Licensed under the GPL
  */
 
 #ifndef __UM_UACCESS_H
diff --git a/arch/um/include/shared/aio.h b/arch/um/include/shared/aio.h
deleted file mode 100644
index 423bae9..0000000
--- a/arch/um/include/shared/aio.h
+++ /dev/null
@@ -1,28 +0,0 @@
-/*
- * Copyright (C) 2004 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
- */
-
-#ifndef AIO_H__
-#define AIO_H__
-
-enum aio_type { AIO_READ, AIO_WRITE, AIO_MMAP };
-
-struct aio_thread_reply {
-	void *data;
-	int err;
-};
-
-struct aio_context {
-	int reply_fd;
-	struct aio_context *next;
-};
-
-#define INIT_AIO_CONTEXT { .reply_fd	= -1, \
-			   .next	= NULL }
-
-extern int submit_aio(enum aio_type type, int fd, char *buf, int len,
-		      unsigned long long offset, int reply_fd,
-                      struct aio_context *aio);
-
-#endif
diff --git a/arch/um/include/shared/arch.h b/arch/um/include/shared/arch.h
index 4f46abd..880ee42 100644
--- a/arch/um/include/shared/arch.h
+++ b/arch/um/include/shared/arch.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __ARCH_H__
diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index ca1843e..5f286ef 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __START_H__
diff --git a/arch/um/include/shared/elf_user.h b/arch/um/include/shared/elf_user.h
index 53516b6..fd461ee 100644
--- a/arch/um/include/shared/elf_user.h
+++ b/arch/um/include/shared/elf_user.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2004 Fujitsu Siemens Computers GmbH
  * Author: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
- * Licensed under the GPL
  */
 
 #ifndef __ELF_USER_H__
diff --git a/arch/um/include/shared/frame_kern.h b/arch/um/include/shared/frame_kern.h
index a5cde5c..ed952ac 100644
--- a/arch/um/include/shared/frame_kern.h
+++ b/arch/um/include/shared/frame_kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __FRAME_KERN_H_
diff --git a/arch/um/include/shared/irq_kern.h b/arch/um/include/shared/irq_kern.h
index e05bd66..7cd1a10 100644
--- a/arch/um/include/shared/irq_kern.h
+++ b/arch/um/include/shared/irq_kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __IRQ_KERN_H__
diff --git a/arch/um/include/shared/irq_user.h b/arch/um/include/shared/irq_user.h
index a7a6120..107751d 100644
--- a/arch/um/include/shared/irq_user.h
+++ b/arch/um/include/shared/irq_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __IRQ_USER_H__
@@ -31,7 +31,6 @@
 struct siginfo;
 extern void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);
 extern void free_irq_by_fd(int fd);
-extern void reactivate_fd(int fd, int irqnum);
 extern void deactivate_fd(int fd, int irqnum);
 extern int deactivate_all_fds(void);
 extern int activate_ipi(int fd, int pid);
diff --git a/arch/um/include/shared/kern.h b/arch/um/include/shared/kern.h
index 6cd0124..3a9c75a 100644
--- a/arch/um/include/shared/kern.h
+++ b/arch/um/include/shared/kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __KERN_H__
diff --git a/arch/um/include/shared/kern_util.h b/arch/um/include/shared/kern_util.h
index 35ab97e..ccafb62 100644
--- a/arch/um/include/shared/kern_util.h
+++ b/arch/um/include/shared/kern_util.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __KERN_UTIL_H__
diff --git a/arch/um/include/shared/longjmp.h b/arch/um/include/shared/longjmp.h
index b3315c1..85a1cc2 100644
--- a/arch/um/include/shared/longjmp.h
+++ b/arch/um/include/shared/longjmp.h
@@ -18,7 +18,7 @@
 	enable = get_signals(); \
 	n = setjmp(*buf); \
 	if(n != 0) \
-		set_signals(enable); \
+		set_signals_trace(enable); \
 	n; })
 
 #endif
diff --git a/arch/um/include/shared/mem.h b/arch/um/include/shared/mem.h
index 5cd40e9..4862c91 100644
--- a/arch/um/include/shared/mem.h
+++ b/arch/um/include/shared/mem.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __MEM_H__
diff --git a/arch/um/include/shared/net_kern.h b/arch/um/include/shared/net_kern.h
index 40442b9..a87be13 100644
--- a/arch/um/include/shared/net_kern.h
+++ b/arch/um/include/shared/net_kern.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_NET_KERN_H
diff --git a/arch/um/include/shared/net_user.h b/arch/um/include/shared/net_user.h
index 3dabbe1..1b05317 100644
--- a/arch/um/include/shared/net_user.h
+++ b/arch/um/include/shared/net_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_NET_USER_H__
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 048ae37..506bcd1 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -1,8 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __OS_H__
@@ -36,6 +36,8 @@
 #define OS_LIB_PATH	"/usr/lib/"
 #endif
 
+#define OS_SENDMSG_MAX_FDS 8
+
 /*
  * types taken from stat_file() in hostfs_user.c
  * (if they are wrong here, they are wrong there...).
@@ -175,6 +177,10 @@
 extern unsigned os_major(unsigned long long dev);
 extern unsigned os_minor(unsigned long long dev);
 extern unsigned long long os_makedev(unsigned major, unsigned minor);
+extern int os_falloc_punch(int fd, unsigned long long offset, int count);
+extern int os_eventfd(unsigned int initval, int flags);
+extern int os_sendmsg_fds(int fd, const void *buf, unsigned int len,
+			  const int *fds, unsigned int fds_num);
 
 /* start_up.c */
 extern void os_early_checks(void);
@@ -231,6 +237,7 @@
 extern void unblock_signals(void);
 extern int get_signals(void);
 extern int set_signals(int enable);
+extern int set_signals_trace(int enable);
 extern int os_is_signal_stack(void);
 extern void deliver_alarm(void);
 
@@ -249,15 +256,13 @@
 
 /* time.c */
 extern void os_idle_sleep(unsigned long long nsecs);
-extern int os_timer_create(void* timer);
-extern int os_timer_set_interval(void* timer, void* its);
-extern int os_timer_one_shot(int ticks);
-extern long long os_timer_disable(void);
-extern long os_timer_remain(void* timer);
+extern int os_timer_create(void);
+extern int os_timer_set_interval(unsigned long long nsecs);
+extern int os_timer_one_shot(unsigned long long nsecs);
+extern void os_timer_disable(void);
 extern void uml_idle_timer(void);
 extern long long os_persistent_clock_emulation(void);
 extern long long os_nsecs(void);
-extern long long os_vnsecs(void);
 
 /* skas/mem.c */
 extern long run_syscall_stub(struct mm_id * mm_idp,
@@ -318,4 +323,10 @@
 
 long syscall(long number, ...);
 
+/* irqflags tracing */
+extern void block_signals_trace(void);
+extern void unblock_signals_trace(void);
+extern void um_trace_signals_on(void);
+extern void um_trace_signals_off(void);
+
 #endif
diff --git a/arch/um/include/shared/ptrace_user.h b/arch/um/include/shared/ptrace_user.h
index 56b2f28..95455e8 100644
--- a/arch/um/include/shared/ptrace_user.h
+++ b/arch/um/include/shared/ptrace_user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __PTRACE_USER_H__
diff --git a/arch/um/include/shared/registers.h b/arch/um/include/shared/registers.h
index a74449b..0c50fa6 100644
--- a/arch/um/include/shared/registers.h
+++ b/arch/um/include/shared/registers.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2004 PathScale, Inc
- * Licensed under the GPL
  */
 
 #ifndef __REGISTERS_H
diff --git a/arch/um/include/shared/sigio.h b/arch/um/include/shared/sigio.h
index 434f1a9..8fe8f57 100644
--- a/arch/um/include/shared/sigio.h
+++ b/arch/um/include/shared/sigio.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __SIGIO_H__
diff --git a/arch/um/include/shared/skas/mm_id.h b/arch/um/include/shared/skas/mm_id.h
index 48dd098..4337b4c 100644
--- a/arch/um/include/shared/skas/mm_id.h
+++ b/arch/um/include/shared/skas/mm_id.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2005 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __MM_ID_H
diff --git a/arch/um/include/shared/skas/skas.h b/arch/um/include/shared/skas/skas.h
index 911f3c4..c93d2cb 100644
--- a/arch/um/include/shared/skas/skas.h
+++ b/arch/um/include/shared/skas/skas.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __SKAS_H
diff --git a/arch/um/include/shared/skas/stub-data.h b/arch/um/include/shared/skas/stub-data.h
index 13f404e..6b01d97 100644
--- a/arch/um/include/shared/skas/stub-data.h
+++ b/arch/um/include/shared/skas/stub-data.h
@@ -1,8 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
 
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2005 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #ifndef __STUB_DATA_H
diff --git a/arch/um/include/shared/timer-internal.h b/arch/um/include/shared/timer-internal.h
index 03e6f21..2d2d13c 100644
--- a/arch/um/include/shared/timer-internal.h
+++ b/arch/um/include/shared/timer-internal.h
@@ -1,7 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2012 - 2014 Cisco Systems
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __TIMER_INTERNAL_H__
@@ -10,4 +10,67 @@
 #define TIMER_MULTIPLIER 256
 #define TIMER_MIN_DELTA  500
 
+enum time_travel_mode {
+	TT_MODE_OFF,
+	TT_MODE_BASIC,
+	TT_MODE_INFCPU,
+};
+
+enum time_travel_timer_mode {
+	TT_TMR_DISABLED,
+	TT_TMR_ONESHOT,
+	TT_TMR_PERIODIC,
+};
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+extern enum time_travel_mode time_travel_mode;
+extern unsigned long long time_travel_time;
+extern enum time_travel_timer_mode time_travel_timer_mode;
+extern unsigned long long time_travel_timer_expiry;
+extern unsigned long long time_travel_timer_interval;
+
+static inline void time_travel_set_time(unsigned long long ns)
+{
+	time_travel_time = ns;
+}
+
+static inline void time_travel_set_timer_mode(enum time_travel_timer_mode mode)
+{
+	time_travel_timer_mode = mode;
+}
+
+static inline void time_travel_set_timer_expiry(unsigned long long expiry)
+{
+	time_travel_timer_expiry = expiry;
+}
+
+static inline void time_travel_set_timer_interval(unsigned long long interval)
+{
+	time_travel_timer_interval = interval;
+}
+#else
+#define time_travel_mode TT_MODE_OFF
+#define time_travel_time 0
+#define time_travel_timer_expiry 0
+#define time_travel_timer_interval 0
+
+static inline void time_travel_set_time(unsigned long long ns)
+{
+}
+
+static inline void time_travel_set_timer_mode(enum time_travel_timer_mode mode)
+{
+}
+
+static inline void time_travel_set_timer_expiry(unsigned long long expiry)
+{
+}
+
+static inline void time_travel_set_timer_interval(unsigned long long interval)
+{
+}
+
+#define time_travel_timer_mode TT_TMR_DISABLED
+#endif
+
 #endif
diff --git a/arch/um/include/shared/um_malloc.h b/arch/um/include/shared/um_malloc.h
index 6395fef..13da932 100644
--- a/arch/um/include/shared/um_malloc.h
+++ b/arch/um/include/shared/um_malloc.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
- * Licensed under the GPL
  */
 
 #ifndef __UM_MALLOC_H__
diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index 4cff19f..e793e42 100644
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __USER_H__
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index 2f36d51..5aa8820 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -1,6 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
 #
 # Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux,intel}.com)
-# Licensed under the GPL
 #
 
 # Don't instrument UML-specific code; without this, we may crash when
@@ -13,7 +13,6 @@
                         -DELF_FORMAT=$(LDS_ELF_FORMAT)	\
 			$(LDS_EXTRA)
 extra-y := vmlinux.lds
-clean-files :=
 
 obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
 	physmem.o process.o ptrace.o reboot.o sigio.o \
diff --git a/arch/um/kernel/config.c.in b/arch/um/kernel/config.c.in
index 972bf16..3ece3c3 100644
--- a/arch/um/kernel/config.c.in
+++ b/arch/um/kernel/config.c.in
@@ -1,6 +1,6 @@
-/* 
+// SPDX-License-Identifier: GPL-2.0
+/*
  * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
index 5568cf8..c69d69e 100644
--- a/arch/um/kernel/dyn.lds.S
+++ b/arch/um/kernel/dyn.lds.S
@@ -70,6 +70,8 @@
     SCHED_TEXT
     CPUIDLE_TEXT
     LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
     *(.fixup)
     *(.stub .text.* .gnu.linkonce.t.*)
     /* .gnu.warning sections are handled specially by elf32.em.  */
@@ -101,7 +103,6 @@
      be empty, which isn't pretty.  */
   . = ALIGN(32 / 8);
   .preinit_array     : { *(.preinit_array) }
-  .init_array     : { *(.init_array) }
   .fini_array     : { *(.fini_array) }
   .data           : {
     INIT_TASK_DATA(KERNEL_STACK_SIZE)
diff --git a/arch/um/kernel/early_printk.c b/arch/um/kernel/early_printk.c
index 4a0800b..c350c23 100644
--- a/arch/um/kernel/early_printk.c
+++ b/arch/um/kernel/early_printk.c
@@ -1,9 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2011 Richard Weinberger <richrd@nod.at>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/kernel.h>
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
index a43d42b..e8fd5d5 100644
--- a/arch/um/kernel/exec.c
+++ b/arch/um/kernel/exec.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/stddef.h>
@@ -32,7 +32,7 @@
 	if (ret) {
 		printk(KERN_ERR "flush_thread - clearing address space failed, "
 		       "err = %d\n", ret);
-		force_sig(SIGKILL, current);
+		force_sig(SIGKILL);
 	}
 	get_safe_registers(current_pt_regs()->regs.gp,
 			   current_pt_regs()->regs.fp);
diff --git a/arch/um/kernel/exitcode.c b/arch/um/kernel/exitcode.c
index 546302e..369fd84 100644
--- a/arch/um/kernel/exitcode.c
+++ b/arch/um/kernel/exitcode.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/ctype.h>
diff --git a/arch/um/kernel/gmon_syms.c b/arch/um/kernel/gmon_syms.c
index f138a4a..9361a8e 100644
--- a/arch/um/kernel/gmon_syms.c
+++ b/arch/um/kernel/gmon_syms.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/module.h>
diff --git a/arch/um/kernel/gprof_syms.c b/arch/um/kernel/gprof_syms.c
index 74ddb44..84d5369 100644
--- a/arch/um/kernel/gprof_syms.c
+++ b/arch/um/kernel/gprof_syms.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/module.h>
diff --git a/arch/um/kernel/initrd.c b/arch/um/kernel/initrd.c
index 6f6e789..c1981ff 100644
--- a/arch/um/kernel/initrd.c
+++ b/arch/um/kernel/initrd.c
@@ -1,10 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/init.h>
-#include <linux/bootmem.h>
+#include <linux/memblock.h>
 #include <linux/initrd.h>
 #include <asm/types.h>
 #include <init.h>
@@ -36,7 +36,9 @@
 		return 0;
 	}
 
-	area = alloc_bootmem(size);
+	area = memblock_alloc(size, SMP_CACHE_BYTES);
+	if (!area)
+		panic("%s: Failed to allocate %llu bytes\n", __func__, size);
 
 	if (load_initrd(initrd, area, size) == -1)
 		return 0;
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 6b7f382..3577118 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -1,8 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 - Cambridge Greys Ltd
  * Copyright (C) 2011 - 2014 Cisco Systems Inc
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
  *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
  */
@@ -21,6 +21,8 @@
 #include <irq_user.h>
 
 
+extern void free_irqs(void);
+
 /* When epoll triggers we do not know why it did so
  * we can also have different IRQs for read and write.
  * This is why we keep a small irq_fd array for each fd -
@@ -100,6 +102,8 @@
 			}
 		}
 	}
+
+	free_irqs();
 }
 
 static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
@@ -244,8 +248,7 @@
 			to_free = NULL;
 		}
 		walk = walk->next;
-		if (to_free != NULL)
-			kfree(to_free);
+		kfree(to_free);
 	}
 }
 
@@ -351,11 +354,6 @@
 }
 
 
-void reactivate_fd(int fd, int irqnum)
-{
-	/** NOP - we do auto-EOI now **/
-}
-
 void deactivate_fd(int fd, int irqnum)
 {
 	struct irq_entry *to_free;
@@ -386,10 +384,8 @@
  */
 int deactivate_all_fds(void)
 {
-	unsigned long flags;
 	struct irq_entry *to_free;
 
-	spin_lock_irqsave(&irq_lock, flags);
 	/* Stop IO. The IRQ loop has no lock so this is our
 	 * only way of making sure we are safe to dispose
 	 * of all IRQ handlers
@@ -405,8 +401,7 @@
 		);
 		to_free = to_free->next;
 	}
-	garbage_collect_irq_entries();
-	spin_unlock_irqrestore(&irq_lock, flags);
+	/* don't garbage collect - we can no longer call kfree() here */
 	os_close_epoll_fd();
 	return 0;
 }
@@ -450,7 +445,6 @@
 }
 
 EXPORT_SYMBOL(um_request_irq);
-EXPORT_SYMBOL(reactivate_fd);
 
 /*
  * irq_chip must define at least enable/disable and ack when
@@ -486,7 +480,7 @@
 	irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);
 
 
-	for (i = 1; i < NR_IRQS; i++)
+	for (i = 1; i <= LAST_IRQ; i++)
 		irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
 	/* Initialize EPOLL Loop */
 	os_setup_epoll();
diff --git a/arch/um/kernel/ksyms.c b/arch/um/kernel/ksyms.c
index 232b223..8ade54a 100644
--- a/arch/um/kernel/ksyms.c
+++ b/arch/um/kernel/ksyms.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/module.h>
@@ -38,6 +38,8 @@
 EXPORT_SYMBOL(os_major);
 EXPORT_SYMBOL(os_minor);
 EXPORT_SYMBOL(os_makedev);
+EXPORT_SYMBOL(os_eventfd);
+EXPORT_SYMBOL(os_sendmsg_fds);
 
 EXPORT_SYMBOL(add_sigio_fd);
 EXPORT_SYMBOL(ignore_sigio_fd);
diff --git a/arch/um/kernel/maccess.c b/arch/um/kernel/maccess.c
index 1f3d5c4..67b2e0f 100644
--- a/arch/um/kernel/maccess.c
+++ b/arch/um/kernel/maccess.c
@@ -1,9 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/uaccess.h>
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index 3c0e470..417ff64 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -1,11 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/stddef.h>
 #include <linux/module.h>
-#include <linux/bootmem.h>
+#include <linux/memblock.h>
 #include <linux/highmem.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
@@ -31,6 +31,7 @@
 
 /* Initialized at boot time, and readonly after that */
 unsigned long long highmem;
+EXPORT_SYMBOL(highmem);
 int kmalloc_ok = 0;
 
 /* Used during early boot */
@@ -46,13 +47,13 @@
 	 */
 	brk_end = (unsigned long) UML_ROUND_UP(sbrk(0));
 	map_memory(brk_end, __pa(brk_end), uml_reserved - brk_end, 1, 1, 0);
-	free_bootmem(__pa(brk_end), uml_reserved - brk_end);
+	memblock_free(__pa(brk_end), uml_reserved - brk_end);
 	uml_reserved = brk_end;
 
 	/* this will put all low memory onto the freelists */
-	free_all_bootmem();
-	max_low_pfn = totalram_pages;
-	max_pfn = totalram_pages;
+	memblock_free_all();
+	max_low_pfn = totalram_pages();
+	max_pfn = max_low_pfn;
 	mem_init_print_info(NULL);
 	kmalloc_ok = 1;
 }
@@ -64,7 +65,12 @@
 static void __init one_page_table_init(pmd_t *pmd)
 {
 	if (pmd_none(*pmd)) {
-		pte_t *pte = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+		pte_t *pte = (pte_t *) memblock_alloc_low(PAGE_SIZE,
+							  PAGE_SIZE);
+		if (!pte)
+			panic("%s: Failed to allocate %lu bytes align=%lx\n",
+			      __func__, PAGE_SIZE, PAGE_SIZE);
+
 		set_pmd(pmd, __pmd(_KERNPG_TABLE +
 					   (unsigned long) __pa(pte)));
 		if (pte != pte_offset_kernel(pmd, 0))
@@ -75,7 +81,11 @@
 static void __init one_md_table_init(pud_t *pud)
 {
 #ifdef CONFIG_3_LEVEL_PGTABLES
-	pmd_t *pmd_table = (pmd_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+	pmd_t *pmd_table = (pmd_t *) memblock_alloc_low(PAGE_SIZE, PAGE_SIZE);
+	if (!pmd_table)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, PAGE_SIZE, PAGE_SIZE);
+
 	set_pud(pud, __pud(_KERNPG_TABLE + (unsigned long) __pa(pmd_table)));
 	if (pmd_table != pmd_offset(pud, 0))
 		BUG();
@@ -124,7 +134,11 @@
 		return;
 
 	fixrange_init( FIXADDR_USER_START, FIXADDR_USER_END, swapper_pg_dir);
-	v = (unsigned long) alloc_bootmem_low_pages(size);
+	v = (unsigned long) memblock_alloc_low(size, PAGE_SIZE);
+	if (!v)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, size, PAGE_SIZE);
+
 	memcpy((void *) v , (void *) FIXADDR_USER_START, size);
 	p = __pa(v);
 	for ( ; size > 0; size -= PAGE_SIZE, vaddr += PAGE_SIZE,
@@ -143,7 +157,12 @@
 	unsigned long zones_size[MAX_NR_ZONES], vaddr;
 	int i;
 
-	empty_zero_page = (unsigned long *) alloc_bootmem_low_pages(PAGE_SIZE);
+	empty_zero_page = (unsigned long *) memblock_alloc_low(PAGE_SIZE,
+							       PAGE_SIZE);
+	if (!empty_zero_page)
+		panic("%s: Failed to allocate %lu bytes align=%lx\n",
+		      __func__, PAGE_SIZE, PAGE_SIZE);
+
 	for (i = 0; i < ARRAY_SIZE(zones_size); i++)
 		zones_size[i] = 0;
 
@@ -170,13 +189,6 @@
 {
 }
 
-#ifdef CONFIG_BLK_DEV_INITRD
-void free_initrd_mem(unsigned long start, unsigned long end)
-{
-	free_reserved_area((void *)start, (void *)end, -1, "initrd");
-}
-#endif
-
 /* Allocate and free page tables. */
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
@@ -197,28 +209,6 @@
 	free_page((unsigned long) pgd);
 }
 
-pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
-{
-	pte_t *pte;
-
-	pte = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
-	return pte;
-}
-
-pgtable_t pte_alloc_one(struct mm_struct *mm, unsigned long address)
-{
-	struct page *pte;
-
-	pte = alloc_page(GFP_KERNEL|__GFP_ZERO);
-	if (!pte)
-		return NULL;
-	if (!pgtable_page_ctor(pte)) {
-		__free_page(pte);
-		return NULL;
-	}
-	return pte;
-}
-
 #ifdef CONFIG_3_LEVEL_PGTABLES
 pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
 {
diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
index f02596e..e7c7b53 100644
--- a/arch/um/kernel/physmem.c
+++ b/arch/um/kernel/physmem.c
@@ -1,10 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/module.h>
-#include <linux/bootmem.h>
+#include <linux/memblock.h>
 #include <linux/mm.h>
 #include <linux/pfn.h>
 #include <asm/page.h>
@@ -80,28 +80,23 @@
 			  unsigned long len, unsigned long long highmem)
 {
 	unsigned long reserve = reserve_end - start;
-	unsigned long pfn = PFN_UP(__pa(reserve_end));
-	unsigned long delta = (len - reserve) >> PAGE_SHIFT;
-	unsigned long offset, bootmap_size;
-	long map_size;
+	long map_size = len - reserve;
 	int err;
 
-	offset = uml_reserved - uml_physmem;
-	map_size = len - offset;
 	if(map_size <= 0) {
 		os_warn("Too few physical memory! Needed=%lu, given=%lu\n",
-			offset, len);
+			reserve, len);
 		exit(1);
 	}
 
 	physmem_fd = create_mem_file(len + highmem);
 
-	err = os_map_memory((void *) uml_reserved, physmem_fd, offset,
+	err = os_map_memory((void *) reserve_end, physmem_fd, reserve,
 			    map_size, 1, 1, 1);
 	if (err < 0) {
 		os_warn("setup_physmem - mapping %ld bytes of memory at 0x%p "
 			"failed - errno = %d\n", map_size,
-			(void *) uml_reserved, err);
+			(void *) reserve_end, err);
 		exit(1);
 	}
 
@@ -113,9 +108,11 @@
 	os_write_file(physmem_fd, __syscall_stub_start, PAGE_SIZE);
 	os_fsync_file(physmem_fd);
 
-	bootmap_size = init_bootmem(pfn, pfn + delta);
-	free_bootmem(__pa(reserve_end) + bootmap_size,
-		     len - bootmap_size - reserve);
+	memblock_add(__pa(start), len + highmem);
+	memblock_reserve(__pa(start), reserve);
+
+	min_low_pfn = PFN_UP(__pa(reserve_end));
+	max_low_pfn = min_low_pfn + (map_size >> PAGE_SHIFT);
 }
 
 int phys_mapping(unsigned long phys, unsigned long long *offset_out)
@@ -146,6 +143,7 @@
 
 	return fd;
 }
+EXPORT_SYMBOL(phys_mapping);
 
 static int __init uml_mem_setup(char *line, int *add)
 {
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 691b83b..263a8f0 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright 2003 PathScale, Inc.
- * Licensed under the GPL
  */
 
 #include <linux/stddef.h>
@@ -203,10 +203,58 @@
 	kmalloc_ok = save_kmalloc_ok;
 }
 
+static void time_travel_sleep(unsigned long long duration)
+{
+	unsigned long long next = time_travel_time + duration;
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_disable();
+
+	while (time_travel_timer_mode == TT_TMR_PERIODIC &&
+	       time_travel_timer_expiry < time_travel_time)
+		time_travel_set_timer_expiry(time_travel_timer_expiry +
+					     time_travel_timer_interval);
+
+	if (time_travel_timer_mode != TT_TMR_DISABLED &&
+	    time_travel_timer_expiry < next) {
+		if (time_travel_timer_mode == TT_TMR_ONESHOT)
+			time_travel_set_timer_mode(TT_TMR_DISABLED);
+		/*
+		 * In basic mode, time_travel_time will be adjusted in
+		 * the timer IRQ handler so it works even when the signal
+		 * comes from the OS timer, see there.
+		 */
+		if (time_travel_mode != TT_MODE_BASIC)
+			time_travel_set_time(time_travel_timer_expiry);
+
+		deliver_alarm();
+	} else {
+		time_travel_set_time(next);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU) {
+		if (time_travel_timer_mode == TT_TMR_PERIODIC)
+			os_timer_set_interval(time_travel_timer_interval);
+		else if (time_travel_timer_mode == TT_TMR_ONESHOT)
+			os_timer_one_shot(time_travel_timer_expiry - next);
+	}
+}
+
+static void um_idle_sleep(void)
+{
+	unsigned long long duration = UM_NSEC_PER_SEC;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_sleep(duration);
+	} else {
+		os_idle_sleep(duration);
+	}
+}
+
 void arch_cpu_idle(void)
 {
 	cpu_tasks[current_thread_info()->cpu].pid = os_getpid();
-	os_idle_sleep(UM_NSEC_PER_SEC);
+	um_idle_sleep();
 	local_irq_enable();
 }
 
diff --git a/arch/um/kernel/ptrace.c b/arch/um/kernel/ptrace.c
index 1a1d88a..b425f47 100644
--- a/arch/um/kernel/ptrace.c
+++ b/arch/um/kernel/ptrace.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/audit.h>
@@ -66,7 +66,7 @@
 
 #ifdef PTRACE_GETREGS
 	case PTRACE_GETREGS: { /* Get all gp regs from the child. */
-		if (!access_ok(VERIFY_WRITE, p, MAX_REG_OFFSET)) {
+		if (!access_ok(p, MAX_REG_OFFSET)) {
 			ret = -EIO;
 			break;
 		}
@@ -81,7 +81,7 @@
 #ifdef PTRACE_SETREGS
 	case PTRACE_SETREGS: { /* Set all gp regs in the child. */
 		unsigned long tmp = 0;
-		if (!access_ok(VERIFY_READ, p, MAX_REG_OFFSET)) {
+		if (!access_ok(p, MAX_REG_OFFSET)) {
 			ret = -EIO;
 			break;
 		}
@@ -112,13 +112,12 @@
 	return ret;
 }
 
-static void send_sigtrap(struct task_struct *tsk, struct uml_pt_regs *regs,
-		  int error_code)
+static void send_sigtrap(struct uml_pt_regs *regs, int error_code)
 {
 	/* Send us the fake SIGTRAP */
 	force_sig_fault(SIGTRAP, TRAP_BRKPT,
 			/* User-mode eip? */
-			UPT_IS_USER(regs) ? (void __user *) UPT_IP(regs) : NULL, tsk);
+			UPT_IS_USER(regs) ? (void __user *) UPT_IP(regs) : NULL);
 }
 
 /*
@@ -147,7 +146,7 @@
 
 	/* Fake a debug trap */
 	if (ptraced & PT_DTRACE)
-		send_sigtrap(current, &regs->regs, 0);
+		send_sigtrap(&regs->regs, 0);
 
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
 		return;
diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
index 71f3e92..48c0610 100644
--- a/arch/um/kernel/reboot.c
+++ b/arch/um/kernel/reboot.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/sched/signal.h>
diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
index b5e0cbb..10c99e0 100644
--- a/arch/um/kernel/sigio.c
+++ b/arch/um/kernel/sigio.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
- * Licensed under the GPL
  */
 
 #include <linux/interrupt.h>
@@ -16,7 +16,6 @@
 	char c;
 
 	os_read_file(sigio_irq_fd, &c, sizeof(c));
-	reactivate_fd(sigio_irq_fd, SIGIO_WRITE_IRQ);
 	return IRQ_HANDLED;
 }
 
diff --git a/arch/um/kernel/signal.c b/arch/um/kernel/signal.c
index 57acbd6..3d57c71 100644
--- a/arch/um/kernel/signal.c
+++ b/arch/um/kernel/signal.c
@@ -1,20 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/module.h>
 #include <linux/ptrace.h>
 #include <linux/sched.h>
+#include <linux/ftrace.h>
 #include <asm/siginfo.h>
 #include <asm/signal.h>
 #include <asm/unistd.h>
 #include <frame_kern.h>
 #include <kern_util.h>
+#include <os.h>
 
 EXPORT_SYMBOL(block_signals);
 EXPORT_SYMBOL(unblock_signals);
 
+void block_signals_trace(void)
+{
+	block_signals();
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
+void unblock_signals_trace(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+	unblock_signals();
+}
+
+void um_trace_signals_on(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+}
+
+void um_trace_signals_off(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
 /*
  * OK, we're invoking a handler
  */
diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
index 0b76d88..f3d494a 100644
--- a/arch/um/kernel/skas/Makefile
+++ b/arch/um/kernel/skas/Makefile
@@ -1,6 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
 #
 # Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
-# Licensed under the GPL
 #
 
 obj-y := clone.o mmu.o process.o syscall.o uaccess.o
@@ -12,4 +12,6 @@
 CFLAGS_clone.o := $(CFLAGS_NO_HARDENING)
 UNPROFILE_OBJS := clone.o
 
+KCOV_INSTRUMENT := n
+
 include arch/um/scripts/Makefile.rules
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index 0f25d41..bfb70c4 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <signal.h>
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index 7a1f2a9..b5e3d91 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/mm.h>
@@ -63,12 +63,12 @@
 	if (current->mm != NULL && current->mm != &init_mm)
 		from_mm = &current->mm->context;
 
-	block_signals();
+	block_signals_trace();
 	if (from_mm)
 		to_mm->id.u.pid = copy_context_skas0(stack,
 						     from_mm->id.u.pid);
 	else to_mm->id.u.pid = start_userspace(stack);
-	unblock_signals();
+	unblock_signals_trace();
 
 	if (to_mm->id.u.pid < 0) {
 		ret = to_mm->id.u.pid;
@@ -119,7 +119,7 @@
 	return;
 
 out:
-	force_sigsegv(SIGSEGV, current);
+	force_sigsegv(SIGSEGV);
 }
 
 void arch_exit_mmap(struct mm_struct *mm)
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index d4dbf08..f2ac134 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/init.h>
@@ -19,7 +19,7 @@
 {
 	int pid;
 
-	block_signals();
+	block_signals_trace();
 	pid = os_getpid();
 
 	cpu_tasks[0].pid = pid;
diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index b783ac8..f574b18 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/kernel.h>
@@ -10,12 +10,23 @@
 #include <sysdep/ptrace.h>
 #include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
+#include <shared/timer-internal.h>
 
 void handle_syscall(struct uml_pt_regs *r)
 {
 	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
 	int syscall;
 
+	/*
+	 * If we have infinite CPU resources, then make every syscall also a
+	 * preemption point, since we don't have any other preemption in this
+	 * case, and kernel threads would basically never run until userspace
+	 * went to sleep, even if said userspace interacts with the kernel in
+	 * various ways.
+	 */
+	if (time_travel_mode == TT_MODE_INFCPU)
+		schedule();
+
 	/* Initialize the syscall number and default return value. */
 	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
 	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
index d450797..3236052 100644
--- a/arch/um/kernel/skas/uaccess.c
+++ b/arch/um/kernel/skas/uaccess.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/err.h>
@@ -59,30 +59,30 @@
 static int do_op_one_page(unsigned long addr, int len, int is_write,
 		 int (*op)(unsigned long addr, int len, void *arg), void *arg)
 {
-	jmp_buf buf;
 	struct page *page;
 	pte_t *pte;
-	int n, faulted;
+	int n;
 
 	pte = maybe_map(addr, is_write);
 	if (pte == NULL)
 		return -1;
 
 	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	addr = (unsigned long) page_address(page) +
+		(addr & ~PAGE_MASK);
+#else
 	addr = (unsigned long) kmap_atomic(page) +
 		(addr & ~PAGE_MASK);
+#endif
+	n = (*op)(addr, len, arg);
 
-	current->thread.fault_catcher = &buf;
-
-	faulted = UML_SETJMP(&buf);
-	if (faulted == 0)
-		n = (*op)(addr, len, arg);
-	else
-		n = -1;
-
-	current->thread.fault_catcher = NULL;
-
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
 	kunmap_atomic((void *)addr);
+#endif
 
 	return n;
 }
diff --git a/arch/um/kernel/stacktrace.c b/arch/um/kernel/stacktrace.c
index ebe7bcf..86df521 100644
--- a/arch/um/kernel/stacktrace.c
+++ b/arch/um/kernel/stacktrace.c
@@ -1,11 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2013 Richard Weinberger <richard@nod.at>
  * Copyright (C) 2014 Google Inc., Author: Daniel Walter <dwalter@google.com>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/kallsyms.h>
@@ -63,8 +60,6 @@
 static void __save_stack_trace(struct task_struct *tsk, struct stack_trace *trace)
 {
 	dump_trace(tsk, &dump_ops, trace);
-	if (trace->nr_entries < trace->max_entries)
-		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
 
 void save_stack_trace(struct stack_trace *trace)
diff --git a/arch/um/kernel/syscall.c b/arch/um/kernel/syscall.c
index 35f7047..eed54c5 100644
--- a/arch/um/kernel/syscall.c
+++ b/arch/um/kernel/syscall.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/file.h>
diff --git a/arch/um/kernel/sysrq.c b/arch/um/kernel/sysrq.c
index 6b995e8..c71b5ef 100644
--- a/arch/um/kernel/sysrq.c
+++ b/arch/um/kernel/sysrq.c
@@ -1,10 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
  */
 
 #include <linux/kallsyms.h>
@@ -20,7 +17,7 @@
 
 static void _print_addr(void *data, unsigned long address, int reliable)
 {
-	pr_info(" [<%08lx>] %s%pF\n", address, reliable ? "" : "? ",
+	pr_info(" [<%08lx>] %s%pS\n", address, reliable ? "" : "? ",
 		(void *)address);
 }
 
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 052de4c..94ea87b 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2012-2014 Cisco Systems
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/clockchips.h>
@@ -19,11 +19,37 @@
 #include <kern_util.h>
 #include <os.h>
 #include <timer-internal.h>
+#include <shared/init.h>
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+enum time_travel_mode time_travel_mode;
+unsigned long long time_travel_time;
+enum time_travel_timer_mode time_travel_timer_mode;
+unsigned long long time_travel_timer_expiry;
+unsigned long long time_travel_timer_interval;
+
+static bool time_travel_start_set;
+static unsigned long long time_travel_start;
+#else
+#define time_travel_start_set 0
+#define time_travel_start 0
+#endif
 
 void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 {
 	unsigned long flags;
 
+	/*
+	 * In basic time-travel mode we still get real interrupts
+	 * (signals) but since we don't read time from the OS, we
+	 * must update the simulated time here to the expiry when
+	 * we get a signal.
+	 * This is not the case in inf-cpu mode, since there we
+	 * never get any real signals from the OS.
+	 */
+	if (time_travel_mode == TT_MODE_BASIC)
+		time_travel_set_time(time_travel_timer_expiry);
+
 	local_irq_save(flags);
 	do_IRQ(TIMER_IRQ, regs);
 	local_irq_restore(flags);
@@ -31,32 +57,56 @@
 
 static int itimer_shutdown(struct clock_event_device *evt)
 {
-	os_timer_disable();
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_set_timer_mode(TT_TMR_DISABLED);
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_disable();
+
 	return 0;
 }
 
 static int itimer_set_periodic(struct clock_event_device *evt)
 {
-	os_timer_set_interval(NULL, NULL);
+	unsigned long long interval = NSEC_PER_SEC / HZ;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_set_timer_mode(TT_TMR_PERIODIC);
+		time_travel_set_timer_expiry(time_travel_time + interval);
+		time_travel_set_timer_interval(interval);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		os_timer_set_interval(interval);
+
 	return 0;
 }
 
 static int itimer_next_event(unsigned long delta,
 			     struct clock_event_device *evt)
 {
-	return os_timer_one_shot(delta);
+	delta += 1;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_set_timer_mode(TT_TMR_ONESHOT);
+		time_travel_set_timer_expiry(time_travel_time + delta);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU)
+		return os_timer_one_shot(delta);
+
+	return 0;
 }
 
 static int itimer_one_shot(struct clock_event_device *evt)
 {
-	os_timer_one_shot(1);
-	return 0;
+	return itimer_next_event(0, evt);
 }
 
 static struct clock_event_device timer_clockevent = {
 	.name			= "posix-timer",
 	.rating			= 250,
-	.cpumask		= cpu_all_mask,
+	.cpumask		= cpu_possible_mask,
 	.features		= CLOCK_EVT_FEAT_PERIODIC |
 				  CLOCK_EVT_FEAT_ONESHOT,
 	.set_state_shutdown	= itimer_shutdown,
@@ -87,6 +137,17 @@
 
 static u64 timer_read(struct clocksource *cs)
 {
+	if (time_travel_mode != TT_MODE_OFF) {
+		/*
+		 * We make reading the timer cost a bit so that we don't get
+		 * stuck in loops that expect time to move more than the
+		 * exact requested sleep amount, e.g. python's socket server,
+		 * see https://bugs.python.org/issue37026.
+		 */
+		time_travel_set_time(time_travel_time + TIMER_MULTIPLIER);
+		return time_travel_time / TIMER_MULTIPLIER;
+	}
+
 	return os_nsecs() / TIMER_MULTIPLIER;
 }
 
@@ -107,7 +168,7 @@
 		printk(KERN_ERR "register_timer : request_irq failed - "
 		       "errno = %d\n", -err);
 
-	err = os_timer_create(NULL);
+	err = os_timer_create();
 	if (err != 0) {
 		printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
 		return;
@@ -123,7 +184,12 @@
 
 void read_persistent_clock64(struct timespec64 *ts)
 {
-	long long nsecs = os_persistent_clock_emulation();
+	long long nsecs;
+
+	if (time_travel_start_set)
+		nsecs = time_travel_start + time_travel_time;
+	else
+		nsecs = os_persistent_clock_emulation();
 
 	set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
 				  nsecs % NSEC_PER_SEC);
@@ -134,3 +200,65 @@
 	timer_set_signal_handler();
 	late_time_init = um_timer_setup;
 }
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+unsigned long calibrate_delay_is_known(void)
+{
+	if (time_travel_mode == TT_MODE_INFCPU)
+		return 1;
+	return 0;
+}
+
+int setup_time_travel(char *str)
+{
+	if (strcmp(str, "=inf-cpu") == 0) {
+		time_travel_mode = TT_MODE_INFCPU;
+		timer_clockevent.name = "time-travel-timer-infcpu";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	if (!*str) {
+		time_travel_mode = TT_MODE_BASIC;
+		timer_clockevent.name = "time-travel-timer";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	return -EINVAL;
+}
+
+__setup("time-travel", setup_time_travel);
+__uml_help(setup_time_travel,
+"time-travel\n"
+"This option just enables basic time travel mode, in which the clock/timers\n"
+"inside the UML instance skip forward when there's nothing to do, rather than\n"
+"waiting for real time to elapse. However, instance CPU speed is limited by\n"
+"the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
+"clock (but quicker when there's nothing to do).\n"
+"\n"
+"time-travel=inf-cpu\n"
+"This enables time travel mode with infinite processing power, in which there\n"
+"are no wall clock timers, and any CPU processing happens - as seen from the\n"
+"guest - instantly. This can be useful for accurate simulation regardless of\n"
+"debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
+"easily lead to getting stuck (e.g. if anything in the system busy loops).\n");
+
+int setup_time_travel_start(char *str)
+{
+	int err;
+
+	err = kstrtoull(str, 0, &time_travel_start);
+	if (err)
+		return err;
+
+	time_travel_start_set = 1;
+	return 1;
+}
+
+__setup("time-travel-start", setup_time_travel_start);
+__uml_help(setup_time_travel_start,
+"time-travel-start=<seconds>\n"
+"Configure the UML instance's wall clock to start at this value rather than\n"
+"the host's wall clock at the time of UML boot.\n");
+#endif
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
index 37508b1..b7eaf65 100644
--- a/arch/um/kernel/tlb.c
+++ b/arch/um/kernel/tlb.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/mm.h>
@@ -37,17 +37,19 @@
 			} mprotect;
 		} u;
 	} ops[1];
+	int userspace;
 	int index;
-	struct mm_id *id;
+	struct mm_struct *mm;
 	void *data;
 	int force;
 };
 
-#define INIT_HVC(mm, force) \
+#define INIT_HVC(mm, force, userspace) \
 	((struct host_vm_change) \
 	 { .ops		= { { .type = NONE } },	\
-	   .id		= &mm->context.id, \
+	   .mm		= mm, \
        	   .data	= NULL, \
+	   .userspace	= userspace, \
 	   .index	= 0, \
 	   .force	= force })
 
@@ -68,18 +70,40 @@
 		op = &hvc->ops[i];
 		switch (op->type) {
 		case MMAP:
-			ret = map(hvc->id, op->u.mmap.addr, op->u.mmap.len,
-				  op->u.mmap.prot, op->u.mmap.fd,
-				  op->u.mmap.offset, finished, &hvc->data);
+			if (hvc->userspace)
+				ret = map(&hvc->mm->context.id, op->u.mmap.addr,
+					  op->u.mmap.len, op->u.mmap.prot,
+					  op->u.mmap.fd,
+					  op->u.mmap.offset, finished,
+					  &hvc->data);
+			else
+				map_memory(op->u.mmap.addr, op->u.mmap.offset,
+					   op->u.mmap.len, 1, 1, 1);
 			break;
 		case MUNMAP:
-			ret = unmap(hvc->id, op->u.munmap.addr,
-				    op->u.munmap.len, finished, &hvc->data);
+			if (hvc->userspace)
+				ret = unmap(&hvc->mm->context.id,
+					    op->u.munmap.addr,
+					    op->u.munmap.len, finished,
+					    &hvc->data);
+			else
+				ret = os_unmap_memory(
+					(void *) op->u.munmap.addr,
+						      op->u.munmap.len);
+
 			break;
 		case MPROTECT:
-			ret = protect(hvc->id, op->u.mprotect.addr,
-				      op->u.mprotect.len, op->u.mprotect.prot,
-				      finished, &hvc->data);
+			if (hvc->userspace)
+				ret = protect(&hvc->mm->context.id,
+					      op->u.mprotect.addr,
+					      op->u.mprotect.len,
+					      op->u.mprotect.prot,
+					      finished, &hvc->data);
+			else
+				ret = os_protect_memory(
+					(void *) op->u.mprotect.addr,
+							op->u.mprotect.len,
+							1, 1, 1);
 			break;
 		default:
 			printk(KERN_ERR "Unknown op type %d in do_ops\n",
@@ -100,9 +124,12 @@
 {
 	__u64 offset;
 	struct host_vm_op *last;
-	int fd, ret = 0;
+	int fd = -1, ret = 0;
 
-	fd = phys_mapping(phys, &offset);
+	if (hvc->userspace)
+		fd = phys_mapping(phys, &offset);
+	else
+		offset = phys;
 	if (hvc->index != 0) {
 		last = &hvc->ops[hvc->index - 1];
 		if ((last->type == MMAP) &&
@@ -215,10 +242,11 @@
 		prot = ((r ? UM_PROT_READ : 0) | (w ? UM_PROT_WRITE : 0) |
 			(x ? UM_PROT_EXEC : 0));
 		if (hvc->force || pte_newpage(*pte)) {
-			if (pte_present(*pte))
-				ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
-					       PAGE_SIZE, prot, hvc);
-			else
+			if (pte_present(*pte)) {
+				if (pte_newpage(*pte))
+					ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+						       PAGE_SIZE, prot, hvc);
+			} else
 				ret = add_munmap(addr, PAGE_SIZE, hvc);
 		} else if (pte_newprot(*pte))
 			ret = add_mprotect(addr, PAGE_SIZE, prot, hvc);
@@ -277,9 +305,9 @@
 	pgd_t *pgd;
 	struct host_vm_change hvc;
 	unsigned long addr = start_addr, next;
-	int ret = 0;
+	int ret = 0, userspace = 1;
 
-	hvc = INIT_HVC(mm, force);
+	hvc = INIT_HVC(mm, force, userspace);
 	pgd = pgd_offset(mm, addr);
 	do {
 		next = pgd_addr_end(addr, end_addr);
@@ -301,7 +329,7 @@
 		       "process: %d\n", task_tgid_vnr(current));
 		/* We are under mmap_sem, release it such that current can terminate */
 		up_write(&current->mm->mmap_sem);
-		force_sig(SIGKILL, current);
+		force_sig(SIGKILL);
 		do_signal(&current->thread.regs);
 	}
 }
@@ -314,9 +342,11 @@
 	pmd_t *pmd;
 	pte_t *pte;
 	unsigned long addr, last;
-	int updated = 0, err;
+	int updated = 0, err = 0, force = 0, userspace = 0;
+	struct host_vm_change hvc;
 
 	mm = &init_mm;
+	hvc = INIT_HVC(mm, force, userspace);
 	for (addr = start; addr < end;) {
 		pgd = pgd_offset(mm, addr);
 		if (!pgd_present(*pgd)) {
@@ -325,8 +355,7 @@
 				last = end;
 			if (pgd_newpage(*pgd)) {
 				updated = 1;
-				err = os_unmap_memory((void *) addr,
-						      last - addr);
+				err = add_munmap(addr, last - addr, &hvc);
 				if (err < 0)
 					panic("munmap failed, errno = %d\n",
 					      -err);
@@ -342,8 +371,7 @@
 				last = end;
 			if (pud_newpage(*pud)) {
 				updated = 1;
-				err = os_unmap_memory((void *) addr,
-						      last - addr);
+				err = add_munmap(addr, last - addr, &hvc);
 				if (err < 0)
 					panic("munmap failed, errno = %d\n",
 					      -err);
@@ -359,8 +387,7 @@
 				last = end;
 			if (pmd_newpage(*pmd)) {
 				updated = 1;
-				err = os_unmap_memory((void *) addr,
-						      last - addr);
+				err = add_munmap(addr, last - addr, &hvc);
 				if (err < 0)
 					panic("munmap failed, errno = %d\n",
 					      -err);
@@ -372,22 +399,25 @@
 		pte = pte_offset_kernel(pmd, addr);
 		if (!pte_present(*pte) || pte_newpage(*pte)) {
 			updated = 1;
-			err = os_unmap_memory((void *) addr,
-					      PAGE_SIZE);
+			err = add_munmap(addr, PAGE_SIZE, &hvc);
 			if (err < 0)
 				panic("munmap failed, errno = %d\n",
 				      -err);
 			if (pte_present(*pte))
-				map_memory(addr,
-					   pte_val(*pte) & PAGE_MASK,
-					   PAGE_SIZE, 1, 1, 1);
+				err = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+					       PAGE_SIZE, 0, &hvc);
 		}
 		else if (pte_newprot(*pte)) {
 			updated = 1;
-			os_protect_memory((void *) addr, PAGE_SIZE, 1, 1, 1);
+			err = add_mprotect(addr, PAGE_SIZE, 0, &hvc);
 		}
 		addr += PAGE_SIZE;
 	}
+	if (!err)
+		err = do_ops(&hvc, hvc.index, 1);
+
+	if (err < 0)
+		panic("flush_tlb_kernel failed, errno = %d\n", err);
 	return updated;
 }
 
@@ -457,7 +487,7 @@
 
 kill:
 	printk(KERN_ERR "Failed to flush page for address 0x%lx\n", address);
-	force_sig(SIGKILL, current);
+	force_sig(SIGKILL);
 }
 
 pgd_t *pgd_offset_proc(struct mm_struct *mm, unsigned long address)
@@ -491,6 +521,13 @@
 
 void flush_tlb_all(void)
 {
+	/*
+	 * Don't bother flushing if this address space is about to be
+	 * destroyed.
+	 */
+	if (atomic_read(&current->mm->mm_users) == 0)
+		return;
+
 	flush_tlb_mm(current->mm);
 }
 
@@ -512,6 +549,13 @@
 static void fix_range(struct mm_struct *mm, unsigned long start_addr,
 		      unsigned long end_addr, int force)
 {
+	/*
+	 * Don't bother flushing if this address space is about to be
+	 * destroyed.
+	 */
+	if (atomic_read(&mm->mm_users) == 0)
+		return;
+
 	fix_range_common(mm, start_addr, end_addr, force);
 }
 
@@ -527,13 +571,6 @@
 void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 			unsigned long end)
 {
-	/*
-	 * Don't bother flushing if this address space is about to be
-	 * destroyed.
-	 */
-	if (atomic_read(&mm->mm_users) == 0)
-		return;
-
 	fix_range(mm, start, end, 0);
 }
 
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index cced829..e62296c 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/mm.h>
@@ -19,7 +19,7 @@
 #include <skas.h>
 
 /*
- * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
+ * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
  * segv().
  */
 int handle_page_fault(unsigned long address, unsigned long ip,
@@ -163,13 +163,12 @@
 static void bad_segv(struct faultinfo fi, unsigned long ip)
 {
 	current->thread.arch.faultinfo = fi;
-	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi),
-			current);
+	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
 }
 
 void fatal_sigsegv(void)
 {
-	force_sigsegv(SIGSEGV, current);
+	force_sigsegv(SIGSEGV);
 	do_signal(&current->thread.regs);
 	/*
 	 * This is to tell gcc that we're not returning - do_signal
@@ -268,13 +267,11 @@
 
 	if (err == -EACCES) {
 		current->thread.arch.faultinfo = fi;
-		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address,
-				current);
+		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
 	} else {
 		BUG_ON(err != -EFAULT);
 		current->thread.arch.faultinfo = fi;
-		force_sig_fault(SIGSEGV, si_code, (void __user *) address,
-				current);
+		force_sig_fault(SIGSEGV, si_code, (void __user *) address);
 	}
 
 out:
@@ -304,12 +301,11 @@
 	if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
 		struct faultinfo *fi = UPT_FAULTINFO(regs);
 		current->thread.arch.faultinfo = *fi;
-		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi),
-				current);
+		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
 	} else {
 		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
 		       sig, code, err);
-		force_sig(sig, current);
+		force_sig(sig);
 	}
 }
 
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index a818cce..0f40ecc 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/delay.h>
@@ -113,6 +113,7 @@
 
 /* Set in uml_mem_setup and modified in linux_main */
 long long physmem_size = 32 * 1024 * 1024;
+EXPORT_SYMBOL(physmem_size);
 
 static const char *usage_string =
 "User Mode Linux v%s\n"
diff --git a/arch/um/kernel/umid.c b/arch/um/kernel/umid.c
index 10bf4ac..8031a03 100644
--- a/arch/um/kernel/umid.c
+++ b/arch/um/kernel/umid.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <asm/errno.h>
diff --git a/arch/um/kernel/uml.lds.S b/arch/um/kernel/uml.lds.S
index 36b07ec..9f21443 100644
--- a/arch/um/kernel/uml.lds.S
+++ b/arch/um/kernel/uml.lds.S
@@ -31,6 +31,8 @@
     SCHED_TEXT
     CPUIDLE_TEXT
     LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
     *(.fixup)
     /* .gnu.warning sections are handled specially by elf32.em.  */
     *(.gnu.warning)
diff --git a/arch/um/os-Linux/Makefile b/arch/um/os-Linux/Makefile
index ada473b..839915b 100644
--- a/arch/um/os-Linux/Makefile
+++ b/arch/um/os-Linux/Makefile
@@ -1,23 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0
 # 
 # Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
-# Licensed under the GPL
 #
 
 # Don't instrument UML-specific code
 KCOV_INSTRUMENT                := n
 
-obj-y = aio.o execvp.o file.o helper.o irq.o main.o mem.o process.o \
+obj-y = execvp.o file.o helper.o irq.o main.o mem.o process.o \
 	registers.o sigio.o signal.o start_up.o time.o tty.o \
 	umid.o user_syms.o util.o drivers/ skas/
 
 obj-$(CONFIG_ARCH_REUSE_HOST_VSYSCALL_AREA) += elf_aux.o
 
-USER_OBJS := $(user-objs-y) aio.o elf_aux.o execvp.o file.o helper.o irq.o \
+USER_OBJS := $(user-objs-y) elf_aux.o execvp.o file.o helper.o irq.o \
 	main.o mem.o process.o registers.o sigio.o signal.o start_up.o time.o \
 	tty.o umid.o util.o
 
-HAVE_AIO_ABI := $(shell [ -r /usr/include/linux/aio_abi.h ] && \
-	echo -DHAVE_AIO_ABI )
-CFLAGS_aio.o += $(HAVE_AIO_ABI)
-
 include arch/um/scripts/Makefile.rules
diff --git a/arch/um/os-Linux/aio.c b/arch/um/os-Linux/aio.c
deleted file mode 100644
index 014eb35..0000000
--- a/arch/um/os-Linux/aio.c
+++ /dev/null
@@ -1,390 +0,0 @@
-/*
- * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
- */
-
-#include <unistd.h>
-#include <sched.h>
-#include <signal.h>
-#include <errno.h>
-#include <sys/time.h>
-#include <asm/unistd.h>
-#include <aio.h>
-#include <init.h>
-#include <kern_util.h>
-#include <os.h>
-
-struct aio_thread_req {
-	enum aio_type type;
-	int io_fd;
-	unsigned long long offset;
-	char *buf;
-	int len;
-	struct aio_context *aio;
-};
-
-#if defined(HAVE_AIO_ABI)
-#include <linux/aio_abi.h>
-
-/*
- * If we have the headers, we are going to build with AIO enabled.
- * If we don't have aio in libc, we define the necessary stubs here.
- */
-
-#if !defined(HAVE_AIO_LIBC)
-
-static long io_setup(int n, aio_context_t *ctxp)
-{
-	return syscall(__NR_io_setup, n, ctxp);
-}
-
-static long io_submit(aio_context_t ctx, long nr, struct iocb **iocbpp)
-{
-	return syscall(__NR_io_submit, ctx, nr, iocbpp);
-}
-
-static long io_getevents(aio_context_t ctx_id, long min_nr, long nr,
-			 struct io_event *events, struct timespec *timeout)
-{
-	return syscall(__NR_io_getevents, ctx_id, min_nr, nr, events, timeout);
-}
-
-#endif
-
-/*
- * The AIO_MMAP cases force the mmapped page into memory here
- * rather than in whatever place first touches the data.  I used
- * to do this by touching the page, but that's delicate because
- * gcc is prone to optimizing that away.  So, what's done here
- * is we read from the descriptor from which the page was
- * mapped.  The caller is required to pass an offset which is
- * inside the page that was mapped.  Thus, when the read
- * returns, we know that the page is in the page cache, and
- * that it now backs the mmapped area.
- */
-
-static int do_aio(aio_context_t ctx, enum aio_type type, int fd, char *buf,
-		  int len, unsigned long long offset, struct aio_context *aio)
-{
-	struct iocb *iocbp = & ((struct iocb) {
-				    .aio_data       = (unsigned long) aio,
-				    .aio_fildes     = fd,
-				    .aio_buf        = (unsigned long) buf,
-				    .aio_nbytes     = len,
-				    .aio_offset     = offset
-			     });
-	char c;
-
-	switch (type) {
-	case AIO_READ:
-		iocbp->aio_lio_opcode = IOCB_CMD_PREAD;
-		break;
-	case AIO_WRITE:
-		iocbp->aio_lio_opcode = IOCB_CMD_PWRITE;
-		break;
-	case AIO_MMAP:
-		iocbp->aio_lio_opcode = IOCB_CMD_PREAD;
-		iocbp->aio_buf = (unsigned long) &c;
-		iocbp->aio_nbytes = sizeof(c);
-		break;
-	default:
-		printk(UM_KERN_ERR "Bogus op in do_aio - %d\n", type);
-		return -EINVAL;
-	}
-
-	return (io_submit(ctx, 1, &iocbp) > 0) ? 0 : -errno;
-}
-
-/* Initialized in an initcall and unchanged thereafter */
-static aio_context_t ctx = 0;
-
-static int aio_thread(void *arg)
-{
-	struct aio_thread_reply reply;
-	struct io_event event;
-	int err, n, reply_fd;
-
-	os_fix_helper_signals();
-	while (1) {
-		n = io_getevents(ctx, 1, 1, &event, NULL);
-		if (n < 0) {
-			if (errno == EINTR)
-				continue;
-			printk(UM_KERN_ERR "aio_thread - io_getevents failed, "
-			       "errno = %d\n", errno);
-		}
-		else {
-			reply = ((struct aio_thread_reply)
-				{ .data = (void *) (long) event.data,
-						.err	= event.res });
-			reply_fd = ((struct aio_context *) reply.data)->reply_fd;
-			err = write(reply_fd, &reply, sizeof(reply));
-			if (err != sizeof(reply))
-				printk(UM_KERN_ERR "aio_thread - write failed, "
-				       "fd = %d, err = %d\n", reply_fd, errno);
-		}
-	}
-	return 0;
-}
-
-#endif
-
-static int do_not_aio(struct aio_thread_req *req)
-{
-	char c;
-	unsigned long long actual;
-	int n;
-
-	actual = lseek64(req->io_fd, req->offset, SEEK_SET);
-	if (actual != req->offset)
-		return -errno;
-
-	switch (req->type) {
-	case AIO_READ:
-		n = read(req->io_fd, req->buf, req->len);
-		break;
-	case AIO_WRITE:
-		n = write(req->io_fd, req->buf, req->len);
-		break;
-	case AIO_MMAP:
-		n = read(req->io_fd, &c, sizeof(c));
-		break;
-	default:
-		printk(UM_KERN_ERR "do_not_aio - bad request type : %d\n",
-		       req->type);
-		return -EINVAL;
-	}
-
-	if (n < 0)
-		return -errno;
-	return 0;
-}
-
-/* These are initialized in initcalls and not changed */
-static int aio_req_fd_r = -1;
-static int aio_req_fd_w = -1;
-static int aio_pid = -1;
-static unsigned long aio_stack;
-
-static int not_aio_thread(void *arg)
-{
-	struct aio_thread_req req;
-	struct aio_thread_reply reply;
-	int err;
-
-	os_fix_helper_signals();
-	while (1) {
-		err = read(aio_req_fd_r, &req, sizeof(req));
-		if (err != sizeof(req)) {
-			if (err < 0)
-				printk(UM_KERN_ERR "not_aio_thread - "
-				       "read failed, fd = %d, err = %d\n",
-				       aio_req_fd_r,
-				       errno);
-			else {
-				printk(UM_KERN_ERR "not_aio_thread - short "
-				       "read, fd = %d, length = %d\n",
-				       aio_req_fd_r, err);
-			}
-			continue;
-		}
-		err = do_not_aio(&req);
-		reply = ((struct aio_thread_reply) { .data 	= req.aio,
-						     .err	= err });
-		err = write(req.aio->reply_fd, &reply, sizeof(reply));
-		if (err != sizeof(reply))
-			printk(UM_KERN_ERR "not_aio_thread - write failed, "
-			       "fd = %d, err = %d\n", req.aio->reply_fd, errno);
-	}
-
-	return 0;
-}
-
-static int init_aio_24(void)
-{
-	int fds[2], err;
-
-	err = os_pipe(fds, 1, 1);
-	if (err)
-		goto out;
-
-	aio_req_fd_w = fds[0];
-	aio_req_fd_r = fds[1];
-
-	err = os_set_fd_block(aio_req_fd_w, 0);
-	if (err)
-		goto out_close_pipe;
-
-	err = run_helper_thread(not_aio_thread, NULL,
-				CLONE_FILES | CLONE_VM, &aio_stack);
-	if (err < 0)
-		goto out_close_pipe;
-
-	aio_pid = err;
-	goto out;
-
-out_close_pipe:
-	close(fds[0]);
-	close(fds[1]);
-	aio_req_fd_w = -1;
-	aio_req_fd_r = -1;
-out:
-#ifndef HAVE_AIO_ABI
-	printk(UM_KERN_INFO "/usr/include/linux/aio_abi.h not present during "
-	       "build\n");
-#endif
-	printk(UM_KERN_INFO "2.6 host AIO support not used - falling back to "
-	       "I/O thread\n");
-	return 0;
-}
-
-#ifdef HAVE_AIO_ABI
-#define DEFAULT_24_AIO 0
-static int init_aio_26(void)
-{
-	int err;
-
-	if (io_setup(256, &ctx)) {
-		err = -errno;
-		printk(UM_KERN_ERR "aio_thread failed to initialize context, "
-		       "err = %d\n", errno);
-		return err;
-	}
-
-	err = run_helper_thread(aio_thread, NULL,
-				CLONE_FILES | CLONE_VM, &aio_stack);
-	if (err < 0)
-		return err;
-
-	aio_pid = err;
-
-	printk(UM_KERN_INFO "Using 2.6 host AIO\n");
-	return 0;
-}
-
-static int submit_aio_26(enum aio_type type, int io_fd, char *buf, int len,
-			 unsigned long long offset, struct aio_context *aio)
-{
-	struct aio_thread_reply reply;
-	int err;
-
-	err = do_aio(ctx, type, io_fd, buf, len, offset, aio);
-	if (err) {
-		reply = ((struct aio_thread_reply) { .data = aio,
-					 .err  = err });
-		err = write(aio->reply_fd, &reply, sizeof(reply));
-		if (err != sizeof(reply)) {
-			err = -errno;
-			printk(UM_KERN_ERR "submit_aio_26 - write failed, "
-			       "fd = %d, err = %d\n", aio->reply_fd, -err);
-		}
-		else err = 0;
-	}
-
-	return err;
-}
-
-#else
-#define DEFAULT_24_AIO 1
-static int init_aio_26(void)
-{
-	return -ENOSYS;
-}
-
-static int submit_aio_26(enum aio_type type, int io_fd, char *buf, int len,
-			 unsigned long long offset, struct aio_context *aio)
-{
-	return -ENOSYS;
-}
-#endif
-
-/* Initialized in an initcall and unchanged thereafter */
-static int aio_24 = DEFAULT_24_AIO;
-
-static int __init set_aio_24(char *name, int *add)
-{
-	aio_24 = 1;
-	return 0;
-}
-
-__uml_setup("aio=2.4", set_aio_24,
-"aio=2.4\n"
-"    This is used to force UML to use 2.4-style AIO even when 2.6 AIO is\n"
-"    available.  2.4 AIO is a single thread that handles one request at a\n"
-"    time, synchronously.  2.6 AIO is a thread which uses the 2.6 AIO \n"
-"    interface to handle an arbitrary number of pending requests.  2.6 AIO \n"
-"    is not available in tt mode, on 2.4 hosts, or when UML is built with\n"
-"    /usr/include/linux/aio_abi.h not available.  Many distributions don't\n"
-"    include aio_abi.h, so you will need to copy it from a kernel tree to\n"
-"    your /usr/include/linux in order to build an AIO-capable UML\n\n"
-);
-
-static int init_aio(void)
-{
-	int err;
-
-	if (!aio_24) {
-		err = init_aio_26();
-		if (err && (errno == ENOSYS)) {
-			printk(UM_KERN_INFO "2.6 AIO not supported on the "
-			       "host - reverting to 2.4 AIO\n");
-			aio_24 = 1;
-		}
-		else return err;
-	}
-
-	if (aio_24)
-		return init_aio_24();
-
-	return 0;
-}
-
-/*
- * The reason for the __initcall/__uml_exitcall asymmetry is that init_aio
- * needs to be called when the kernel is running because it calls run_helper,
- * which needs get_free_page.  exit_aio is a __uml_exitcall because the generic
- * kernel does not run __exitcalls on shutdown, and can't because many of them
- * break when called outside of module unloading.
- */
-__initcall(init_aio);
-
-static void exit_aio(void)
-{
-	if (aio_pid != -1) {
-		os_kill_process(aio_pid, 1);
-		free_stack(aio_stack, 0);
-	}
-}
-
-__uml_exitcall(exit_aio);
-
-static int submit_aio_24(enum aio_type type, int io_fd, char *buf, int len,
-			 unsigned long long offset, struct aio_context *aio)
-{
-	struct aio_thread_req req = { .type 		= type,
-				      .io_fd		= io_fd,
-				      .offset		= offset,
-				      .buf		= buf,
-				      .len		= len,
-				      .aio		= aio,
-	};
-	int err;
-
-	err = write(aio_req_fd_w, &req, sizeof(req));
-	if (err == sizeof(req))
-		err = 0;
-	else err = -errno;
-
-	return err;
-}
-
-int submit_aio(enum aio_type type, int io_fd, char *buf, int len,
-	       unsigned long long offset, int reply_fd,
-	       struct aio_context *aio)
-{
-	aio->reply_fd = reply_fd;
-	if (aio_24)
-		return submit_aio_24(type, io_fd, buf, len, offset, aio);
-	else
-		return submit_aio_26(type, io_fd, buf, len, offset, aio);
-}
diff --git a/arch/um/os-Linux/drivers/Makefile b/arch/um/os-Linux/drivers/Makefile
index 6c546dc..d79e75f 100644
--- a/arch/um/os-Linux/drivers/Makefile
+++ b/arch/um/os-Linux/drivers/Makefile
@@ -1,6 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
 # 
 # Copyright (C) 2000, 2002 Jeff Dike (jdike@karaya.com)
-# Licensed under the GPL
 #
 
 ethertap-objs := ethertap_kern.o ethertap_user.o
diff --git a/arch/um/os-Linux/drivers/etap.h b/arch/um/os-Linux/drivers/etap.h
index 54183a6..a475259 100644
--- a/arch/um/os-Linux/drivers/etap.h
+++ b/arch/um/os-Linux/drivers/etap.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __DRIVERS_ETAP_H
diff --git a/arch/um/os-Linux/drivers/ethertap_kern.c b/arch/um/os-Linux/drivers/ethertap_kern.c
index f424600..3182e75 100644
--- a/arch/um/os-Linux/drivers/ethertap_kern.c
+++ b/arch/um/os-Linux/drivers/ethertap_kern.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
 #include <linux/init.h>
diff --git a/arch/um/os-Linux/drivers/ethertap_user.c b/arch/um/os-Linux/drivers/ethertap_user.c
index 6d49182..9483021 100644
--- a/arch/um/os-Linux/drivers/ethertap_user.c
+++ b/arch/um/os-Linux/drivers/ethertap_user.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
  * James Leu (jleu@mindspring.net).
  * Copyright (C) 2001 by various other people who didn't put their name here.
- * Licensed under the GPL.
  */
 
 #include <stdio.h>
diff --git a/arch/um/os-Linux/drivers/tuntap.h b/arch/um/os-Linux/drivers/tuntap.h
index 7367354..e364e42 100644
--- a/arch/um/os-Linux/drivers/tuntap.h
+++ b/arch/um/os-Linux/drivers/tuntap.h
@@ -1,6 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #ifndef __UM_TUNTAP_H
diff --git a/arch/um/os-Linux/drivers/tuntap_kern.c b/arch/um/os-Linux/drivers/tuntap_kern.c
index d9d56e5..adcb671 100644
--- a/arch/um/os-Linux/drivers/tuntap_kern.c
+++ b/arch/um/os-Linux/drivers/tuntap_kern.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <linux/netdevice.h>
diff --git a/arch/um/os-Linux/drivers/tuntap_user.c b/arch/um/os-Linux/drivers/tuntap_user.c
index db24ce0..53eb3d5 100644
--- a/arch/um/os-Linux/drivers/tuntap_user.c
+++ b/arch/um/os-Linux/drivers/tuntap_user.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
index c019709..5133e3a 100644
--- a/arch/um/os-Linux/file.c
+++ b/arch/um/os-Linux/file.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
@@ -15,6 +15,7 @@
 #include <sys/sysmacros.h>
 #include <sys/un.h>
 #include <sys/types.h>
+#include <sys/eventfd.h>
 #include <os.h>
 
 static void copy_stat(struct uml_stat *dst, const struct stat64 *src)
@@ -610,3 +611,56 @@
 {
 	return makedev(major, minor);
 }
+
+int os_falloc_punch(int fd, unsigned long long offset, int len)
+{
+	int n = fallocate(fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, offset, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_eventfd(unsigned int initval, int flags)
+{
+	int fd = eventfd(initval, flags);
+
+	if (fd < 0)
+		return -errno;
+	return fd;
+}
+
+int os_sendmsg_fds(int fd, const void *buf, unsigned int len, const int *fds,
+		   unsigned int fds_num)
+{
+	struct iovec iov = {
+		.iov_base = (void *) buf,
+		.iov_len = len,
+	};
+	union {
+		char control[CMSG_SPACE(sizeof(*fds) * OS_SENDMSG_MAX_FDS)];
+		struct cmsghdr align;
+	} u;
+	unsigned int fds_size = sizeof(*fds) * fds_num;
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = u.control,
+		.msg_controllen = CMSG_SPACE(fds_size),
+	};
+	struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+	int err;
+
+	if (fds_num > OS_SENDMSG_MAX_FDS)
+		return -EINVAL;
+	memset(u.control, 0, sizeof(u.control));
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	cmsg->cmsg_len = CMSG_LEN(fds_size);
+	memcpy(CMSG_DATA(cmsg), fds, fds_size);
+	err = sendmsg(fd, &msg, 0);
+
+	if (err < 0)
+		return -errno;
+	return err;
+}
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index 3f02d42..9fa6e41 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
diff --git a/arch/um/os-Linux/irq.c b/arch/um/os-Linux/irq.c
index 3658230..d508310 100644
--- a/arch/um/os-Linux/irq.c
+++ b/arch/um/os-Linux/irq.c
@@ -1,8 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 - Cambridge Greys Ltd
  * Copyright (C) 2011 - 2014 Cisco Systems Inc
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
index f1fee2b..8014dfa 100644
--- a/arch/um/os-Linux/main.c
+++ b/arch/um/os-Linux/main.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
@@ -170,7 +170,7 @@
 	 * that they won't be delivered after the exec, when
 	 * they are definitely not expected.
 	 */
-	unblock_signals();
+	unblock_signals_trace();
 
 	os_info("\n");
 	/* Reboot */
diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index e162a95..3c1b774 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index b3e0d40..e52dd37 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/os-Linux/registers.c b/arch/um/os-Linux/registers.c
index 2ff8d4f..2d92705 100644
--- a/arch/um/os-Linux/registers.c
+++ b/arch/um/os-Linux/registers.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2004 PathScale, Inc
  * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <errno.h>
diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
index 46e762f..7555808 100644
--- a/arch/um/os-Linux/sigio.c
+++ b/arch/um/os-Linux/sigio.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <unistd.h>
@@ -132,7 +132,7 @@
 	int n;
 	char c;
 
-	flags = set_signals(0);
+	flags = set_signals_trace(0);
 	CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
 	if (n != sizeof(c)) {
 		printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
@@ -147,7 +147,7 @@
 		goto fail;
 	}
 
-	set_signals(flags);
+	set_signals_trace(flags);
 	return;
  fail:
 	/* Critical section start */
@@ -161,7 +161,7 @@
 	close(write_sigio_fds[0]);
 	close(write_sigio_fds[1]);
 	/* Critical section end */
-	set_signals(flags);
+	set_signals_trace(flags);
 }
 
 int add_sigio_fd(int fd)
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index bf0acb8..b58bc68 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -1,15 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2004 PathScale, Inc
  * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
 #include <stdarg.h>
 #include <errno.h>
 #include <signal.h>
+#include <string.h>
 #include <strings.h>
 #include <as-layout.h>
 #include <kern_util.h>
@@ -26,34 +27,27 @@
 	[SIGBUS]	= bus_handler,
 	[SIGSEGV]	= segv_handler,
 	[SIGIO]		= sigio_handler,
-	[SIGALRM]	= timer_handler
 };
 
 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 {
-	struct uml_pt_regs *r;
+	struct uml_pt_regs r;
 	int save_errno = errno;
 
-	r = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-	if (!r)
-		panic("out of memory");
-
-	r->is_user = 0;
+	r.is_user = 0;
 	if (sig == SIGSEGV) {
 		/* For segfaults, we want the data from the sigcontext. */
-		get_regs_from_mc(r, mc);
-		GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
+		get_regs_from_mc(&r, mc);
+		GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
 	}
 
 	/* enable signals if sig isn't IRQ signal */
-	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
-		unblock_signals();
+	if ((sig != SIGIO) && (sig != SIGWINCH))
+		unblock_signals_trace();
 
-	(*sig_info[sig])(sig, si, r);
+	(*sig_info[sig])(sig, si, &r);
 
 	errno = save_errno;
-
-	free(r);
 }
 
 /*
@@ -82,26 +76,22 @@
 		return;
 	}
 
-	block_signals();
+	block_signals_trace();
 
 	sig_handler_common(sig, si, mc);
 
-	set_signals(enabled);
+	set_signals_trace(enabled);
 }
 
 static void timer_real_alarm_handler(mcontext_t *mc)
 {
-	struct uml_pt_regs *regs;
-
-	regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-	if (!regs)
-		panic("out of memory");
+	struct uml_pt_regs regs;
 
 	if (mc != NULL)
-		get_regs_from_mc(regs, mc);
-	timer_handler(SIGALRM, NULL, regs);
-
-	free(regs);
+		get_regs_from_mc(&regs, mc);
+	else
+		memset(&regs, 0, sizeof(regs));
+	timer_handler(SIGALRM, NULL, &regs);
 }
 
 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
@@ -114,7 +104,7 @@
 		return;
 	}
 
-	block_signals();
+	block_signals_trace();
 
 	signals_active |= SIGALRM_MASK;
 
@@ -122,7 +112,7 @@
 
 	signals_active &= ~SIGALRM_MASK;
 
-	set_signals(enabled);
+	set_signals_trace(enabled);
 }
 
 void deliver_alarm(void) {
@@ -263,6 +253,8 @@
 	if (signals_enabled == 1)
 		return;
 
+	signals_enabled = 1;
+
 	/*
 	 * We loop because the IRQ handler returns with interrupts off.  So,
 	 * interrupts may have arrived and we need to re-enable them and
@@ -272,12 +264,9 @@
 		/*
 		 * Save and reset save_pending after enabling signals.  This
 		 * way, signals_pending won't be changed while we're reading it.
-		 */
-		signals_enabled = 1;
-
-		/*
+		 *
 		 * Setting signals_enabled and reading signals_pending must
-		 * happen in this order.
+		 * happen in this order, so have the barrier here.
 		 */
 		barrier();
 
@@ -290,10 +279,13 @@
 		/*
 		 * We have pending interrupts, so disable signals, as the
 		 * handlers expect them off when they are called.  They will
-		 * be enabled again above.
+		 * be enabled again above. We need to trace this, as we're
+		 * expected to be enabling interrupts already, but any more
+		 * tracing that happens inside the handlers we call for the
+		 * pending signals will mess up the tracing state.
 		 */
-
 		signals_enabled = 0;
+		um_trace_signals_off();
 
 		/*
 		 * Deal with SIGIO first because the alarm handler might
@@ -316,6 +308,9 @@
 		if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
 			return;
 
+		/* Re-enable signals and trace that we're doing so. */
+		um_trace_signals_on();
+		signals_enabled = 1;
 	}
 }
 
@@ -338,6 +333,21 @@
 	return ret;
 }
 
+int set_signals_trace(int enable)
+{
+	int ret;
+	if (signals_enabled == enable)
+		return enable;
+
+	ret = signals_enabled;
+	if (enable)
+		unblock_signals_trace();
+	else
+		block_signals_trace();
+
+	return ret;
+}
+
 int os_is_signal_stack(void)
 {
 	stack_t ss;
diff --git a/arch/um/os-Linux/skas/Makefile b/arch/um/os-Linux/skas/Makefile
index d2ea340..c4566e7 100644
--- a/arch/um/os-Linux/skas/Makefile
+++ b/arch/um/os-Linux/skas/Makefile
@@ -1,6 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
 #
 # Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
-# Licensed under the GPL
 #
 
 obj-y := mem.o process.o
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
index 35015e3..c546d16 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stddef.h>
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index df4a985..4fb877b 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -1,7 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
@@ -425,9 +425,9 @@
 			case SIGBUS:
 			case SIGFPE:
 			case SIGWINCH:
-				block_signals();
+				block_signals_trace();
 				(*sig_info[sig])(sig, (struct siginfo *)&si, regs);
-				unblock_signals();
+				unblock_signals_trace();
 				break;
 			default:
 				printk(UM_KERN_ERR "userspace - child stopped "
@@ -625,10 +625,10 @@
 	cb_arg = arg;
 	cb_back = &here;
 
-	block_signals();
+	block_signals_trace();
 	if (UML_SETJMP(&here) == 0)
 		UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
-	unblock_signals();
+	unblock_signals_trace();
 
 	cb_proc = NULL;
 	cb_arg = NULL;
@@ -637,13 +637,13 @@
 
 void halt_skas(void)
 {
-	block_signals();
+	block_signals_trace();
 	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
 }
 
 void reboot_skas(void)
 {
-	block_signals();
+	block_signals_trace();
 	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
 }
 
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 82bf5f8..f79dc33 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 0e39b99..432f8e1 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -1,9 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
  * Copyright (C) 2012-2014 Cisco Systems
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stddef.h>
@@ -26,11 +26,11 @@
 
 static inline long long timespec_to_ns(const struct timespec *ts)
 {
-	return ((long long) ts->tv_sec * UM_NSEC_PER_SEC) +
-		ts->tv_nsec;
+	return ((long long) ts->tv_sec * UM_NSEC_PER_SEC) + ts->tv_nsec;
 }
 
-long long os_persistent_clock_emulation (void) {
+long long os_persistent_clock_emulation(void)
+{
 	struct timespec realtime_tp;
 
 	clock_gettime(CLOCK_REALTIME, &realtime_tp);
@@ -40,94 +40,41 @@
 /**
  * os_timer_create() - create an new posix (interval) timer
  */
-int os_timer_create(void* timer) {
+int os_timer_create(void)
+{
+	timer_t *t = &event_high_res_timer;
 
-	timer_t* t = timer;
-
-	if(t == NULL) {
-		t = &event_high_res_timer;
-	}
-
-	if (timer_create(
-		CLOCK_MONOTONIC,
-		NULL,
-		t) == -1) {
+	if (timer_create(CLOCK_MONOTONIC, NULL, t) == -1)
 		return -1;
-	}
-	return 0;
-}
-
-int os_timer_set_interval(void* timer, void* i)
-{
-	struct itimerspec its;
-	unsigned long long nsec;
-	timer_t* t = timer;
-	struct itimerspec* its_in = i;
-
-	if(t == NULL) {
-		t = &event_high_res_timer;
-	}
-
-	nsec = UM_NSEC_PER_SEC / UM_HZ;
-
-	if(its_in != NULL) {
-		its.it_value.tv_sec = its_in->it_value.tv_sec;
-		its.it_value.tv_nsec = its_in->it_value.tv_nsec;
-	} else {
-		its.it_value.tv_sec = 0;
-		its.it_value.tv_nsec = nsec;
-	}
-
-	its.it_interval.tv_sec = 0;
-	its.it_interval.tv_nsec = nsec;
-
-	if(timer_settime(*t, 0, &its, NULL) == -1) {
-		return -errno;
-	}
 
 	return 0;
 }
 
-/**
- * os_timer_remain() - returns the remaining nano seconds of the given interval
- *                     timer
- * Because this is the remaining time of an interval timer, which correspondends
- * to HZ, this value can never be bigger than one second. Just
- * the nanosecond part of the timer is returned.
- * The returned time is relative to the start time of the interval timer.
- * Return an negative value in an error case.
- */
-long os_timer_remain(void* timer)
+int os_timer_set_interval(unsigned long long nsecs)
 {
 	struct itimerspec its;
-	timer_t* t = timer;
 
-	if(t == NULL) {
-		t = &event_high_res_timer;
-	}
+	its.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC;
 
-	if(timer_gettime(t, &its) == -1) {
+	its.it_interval.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_interval.tv_nsec = nsecs % UM_NSEC_PER_SEC;
+
+	if (timer_settime(event_high_res_timer, 0, &its, NULL) == -1)
 		return -errno;
-	}
 
-	return its.it_value.tv_nsec;
+	return 0;
 }
 
-int os_timer_one_shot(int ticks)
+int os_timer_one_shot(unsigned long long nsecs)
 {
-	struct itimerspec its;
-	unsigned long long nsec;
-	unsigned long sec;
+	struct itimerspec its = {
+		.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC,
+		.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC,
 
-    nsec = (ticks + 1);
-    sec = nsec / UM_NSEC_PER_SEC;
-	nsec = nsec % UM_NSEC_PER_SEC;
-
-	its.it_value.tv_sec = nsec / UM_NSEC_PER_SEC;
-	its.it_value.tv_nsec = nsec;
-
-	its.it_interval.tv_sec = 0;
-	its.it_interval.tv_nsec = 0; // we cheat here
+		.it_interval.tv_sec = 0,
+		.it_interval.tv_nsec = 0, // we cheat here
+	};
 
 	timer_settime(event_high_res_timer, 0, &its, NULL);
 	return 0;
@@ -135,24 +82,13 @@
 
 /**
  * os_timer_disable() - disable the posix (interval) timer
- * Returns the remaining interval timer time in nanoseconds
  */
-long long os_timer_disable(void)
+void os_timer_disable(void)
 {
 	struct itimerspec its;
 
 	memset(&its, 0, sizeof(struct itimerspec));
-	timer_settime(event_high_res_timer, 0, &its, &its);
-
-	return its.it_value.tv_sec * UM_NSEC_PER_SEC + its.it_value.tv_nsec;
-}
-
-long long os_vnsecs(void)
-{
-	struct timespec ts;
-
-	clock_gettime(CLOCK_PROCESS_CPUTIME_ID,&ts);
-	return timespec_to_ns(&ts);
+	timer_settime(event_high_res_timer, 0, &its, NULL);
 }
 
 long long os_nsecs(void)
@@ -169,21 +105,14 @@
  */
 void os_idle_sleep(unsigned long long nsecs)
 {
-	struct timespec ts;
-
-	if (nsecs <= 0) {
-		return;
-	}
-
-	ts = ((struct timespec) {
-			.tv_sec  = nsecs / UM_NSEC_PER_SEC,
-			.tv_nsec = nsecs % UM_NSEC_PER_SEC
-	});
+	struct timespec ts = {
+		.tv_sec  = nsecs / UM_NSEC_PER_SEC,
+		.tv_nsec = nsecs % UM_NSEC_PER_SEC
+	};
 
 	/*
 	 * Relay the signal if clock_nanosleep is interrupted.
 	 */
-	if (clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL)) {
+	if (clock_nanosleep(CLOCK_MONOTONIC, 0, &ts, NULL))
 		deliver_alarm();
-	}
 }
diff --git a/arch/um/os-Linux/tty.c b/arch/um/os-Linux/tty.c
index 721d8af..f784db8 100644
--- a/arch/um/os-Linux/tty.c
+++ b/arch/um/os-Linux/tty.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdlib.h>
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 998fbb4..44def53 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>
@@ -135,12 +135,18 @@
  */
 static inline int is_umdir_used(char *dir)
 {
-	char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
-	char pid[sizeof("nnnnn\0")], *end;
+	char pid[sizeof("nnnnn\0")], *end, *file;
 	int dead, fd, p, n, err;
+	size_t filelen;
 
-	n = snprintf(file, sizeof(file), "%s/pid", dir);
-	if (n >= sizeof(file)) {
+	err = asprintf(&file, "%s/pid", dir);
+	if (err < 0)
+		return 0;
+
+	filelen = strlen(file);
+
+	n = snprintf(file, filelen, "%s/pid", dir);
+	if (n >= filelen) {
 		printk(UM_KERN_ERR "is_umdir_used - pid filename too long\n");
 		err = -E2BIG;
 		goto out;
@@ -185,6 +191,7 @@
 out_close:
 	close(fd);
 out:
+	free(file);
 	return 0;
 }
 
@@ -210,18 +217,21 @@
 
 static void __init create_pid_file(void)
 {
-	char file[strlen(uml_dir) + UMID_LEN + sizeof("/pid\0")];
-	char pid[sizeof("nnnnn\0")];
+	char pid[sizeof("nnnnn\0")], *file;
 	int fd, n;
 
-	if (umid_file_name("pid", file, sizeof(file)))
+	file = malloc(strlen(uml_dir) + UMID_LEN + sizeof("/pid\0"));
+	if (!file)
 		return;
 
+	if (umid_file_name("pid", file, sizeof(file)))
+		goto out;
+
 	fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
 	if (fd < 0) {
 		printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
 		       "%s\n", file, strerror(errno));
-		return;
+		goto out;
 	}
 
 	snprintf(pid, sizeof(pid), "%d\n", getpid());
@@ -231,6 +241,8 @@
 		       errno);
 
 	close(fd);
+out:
+	free(file);
 }
 
 int __init set_umid(char *name)
@@ -385,13 +397,19 @@
 
 static void remove_umid_dir(void)
 {
-	char dir[strlen(uml_dir) + UMID_LEN + 1], err;
+	char *dir, err;
+
+	dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
+	if (!dir)
+		return;
 
 	sprintf(dir, "%s%s", uml_dir, umid);
 	err = remove_files_and_dir(dir);
 	if (err)
 		os_warn("%s - remove_files_and_dir failed with err = %d\n",
 			__func__, err);
+
+	free(dir);
 }
 
 __uml_exitcall(remove_umid_dir);
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
index 8cc8b26..ecf2f39 100644
--- a/arch/um/os-Linux/util.c
+++ b/arch/um/os-Linux/util.c
@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
- * Licensed under the GPL
  */
 
 #include <stdio.h>