docs/secure-partition-manager/secure-partition-manager.rst

Foreword
========

- This document describes the FF-A implementation from `[1]`_ for the
  configuration where the SPMC resides at S-EL2 on platforms implementing the
  FEAT_SEL2 architecture extension.
- It is not an architecture specification and it might provide assumptions on
  sections mandated as implementation-defined in the specification.
- It covers the implications of TF-A used as a bootloader, and Hafnium used as a
  reference code base for an SPMC.

Terminology
===========

- The term Hypervisor refers to the NS-EL2 component managing Virtual Machines
  (or partitions) in the normal world.
- The term SPMC refers to the S-EL2 component managing secure partitions in
  the secure world when the FEAT_SEL2 architecture extension is implemented.
- Alternatively, SPMC can refer to an S-EL1 component, itself being a secure
  partition and implementing the FF-A ABI on platforms not implementing the
  FEAT_SEL2 architecture extension.
- The term VM refers to a normal world Virtual Machine managed by an Hypervisor.
- The term SP refers to a secure world "Virtual Machine" managed by an SPMC.

Sample reference stack
======================

The following diagram illustrates a possible configuration when the
FEAT_SEL2 architecture extension is implemented, showing the |SPMD|
and |SPMC|, one or multiple secure partitions, with an optional
Hypervisor:

.. image:: ../resources/diagrams/Hafnium_overview_SPMD.png

Integration with TF-A (Bootloader and SPMD)
===========================================

The `TF-A project`_ provides the reference implementation for the secure monitor
for Arm A class devices, executing at EL3. It includes the implementation of the
|SPMD|, which manages the world-switch, to relay the FF-A calls to the |SPMC|.

TF-A also serves as the system bootlader, and it was used in the reference
implemenation for the SPMC and SPs.
SPs may be signed by different parties (SiP, OEM/ODM, TOS vendor, etc.).
Thus they are supplied as distinct signed entities within the FIP flash
image. The FIP image itself is not signed hence this provides the ability
to upgrade SPs in the field.

TF-A build options
------------------

This section explains the TF-A build options for an FF-A based SPM, in which SPMD
is located at EL3.

This is a step needed for integrating Hafnium as the S-EL2 SPMC and
the TF-A as SPMD, together making the SPM component.

- **SPD=spmd**: this option selects the SPMD component to relay the FF-A
  protocol from NWd to SWd back and forth. It is not possible to
  enable another Secure Payload Dispatcher when this option is chosen.
- **SPMD_SPM_AT_SEL2**: this option adjusts the SPMC exception
  level to being at S-EL2. It defaults to enabled (value 1) when
  SPD=spmd is chosen.The context save/restore routine and exhaustive list
  of registers is visible at `[4]`_. When set the reference software stack
  assumes enablement of FEAT_PAuth, FEAT_BTI and FEAT_MTE architecture
  extensions.
- **SP_LAYOUT_FILE**: this option specifies a text description file
  providing paths to SP binary images and manifests in DTS format
  (see `Secure Partitions Layout File`_). It is required when ``SPMD_SPM_AT_SEL2``
  is enabled, i.e. when multiple secure partitions are to be loaded by BL2 on
  behalf of the SPMC.
- **BL32** option is re-purposed to specify the SPMC image. It can specify either
  the Hafnium binary path (built for the secure world) or the path to a TEE
  binary implementing FF-A interfaces.
- **BL33** option to specify normal world loader such as U-Boot or the UEFI
  framework payload, which would use FF-A calls during runtime to interact with
  Hafnium as the SPMC.

As a result of configuring ``SPD=spmd`` and ``SPMD_SPM_AT_SEL2`` TF-A provides
context save/restore operations when entering/exiting an EL2 execution context.

There are other build options that relate support other valid FF-A
system configurations where the SPMC is implemented at S-EL1 and EL3.
Note that they conflict with those needed to integrate with Hafnium as the SPMC.
For more details refer to |TF-A| build options `[10]`_.

Sample TF-A build command line when FEAT_SEL2 architecture extension is
implemented and the SPMC is located at S-EL2, for Arm's FVP platform:

.. code:: shell

    make \
    CROSS_COMPILE=aarch64-none-elf- \
    PLAT=fvp \
    SPD=spmd \
    ARM_ARCH_MINOR=5 \
    BRANCH_PROTECTION=1 \
    CTX_INCLUDE_PAUTH_REGS=1 \
    CTX_INCLUDE_MTE_REGS=1 \
    BL32=<path-to-hafnium-binary> \
    BL33=<path-to-bl33-binary> \
    SP_LAYOUT_FILE=sp_layout.json \
    all fip

Sample TF-A build command line when FEAT_SEL2 architecture extension is
implemented, the SPMC is located at S-EL2, and enabling secure boot:

.. code:: shell

    make \
    CROSS_COMPILE=aarch64-none-elf- \
    PLAT=fvp \
    SPD=spmd \
    ARM_ARCH_MINOR=5 \
    BRANCH_PROTECTION=1 \
    CTX_INCLUDE_PAUTH_REGS=1 \
    CTX_INCLUDE_MTE_REGS=1 \
    BL32=<path-to-hafnium-binary> \
    BL33=<path-to-bl33-binary> \
    SP_LAYOUT_FILE=sp_layout.json \
    MBEDTLS_DIR=<path-to-mbedtls-lib> \
    TRUSTED_BOARD_BOOT=1 \
    COT=dualroot \
    ARM_ROTPK_LOCATION=devel_rsa \
    ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem \
    GENERATE_COT=1 \
    all fip

FVP model invocation
--------------------

The FVP command line needs the following options to exercise the S-EL2 SPMC:

+---------------------------------------------------+------------------------------------+
| - cluster0.has_arm_v8-5=1                         | Implements FEAT_SEL2, FEAT_PAuth,  |
| - cluster1.has_arm_v8-5=1                         | and FEAT_BTI.                      |
+---------------------------------------------------+------------------------------------+
| - pci.pci_smmuv3.mmu.SMMU_AIDR=2                  | Parameters required for the        |
| - pci.pci_smmuv3.mmu.SMMU_IDR0=0x0046123B         | SMMUv3.2 modeling.                 |
| - pci.pci_smmuv3.mmu.SMMU_IDR1=0x00600002         |                                    |
| - pci.pci_smmuv3.mmu.SMMU_IDR3=0x1714             |                                    |
| - pci.pci_smmuv3.mmu.SMMU_IDR5=0xFFFF0472         |                                    |
| - pci.pci_smmuv3.mmu.SMMU_S_IDR1=0xA0000002       |                                    |
| - pci.pci_smmuv3.mmu.SMMU_S_IDR2=0                |                                    |
| - pci.pci_smmuv3.mmu.SMMU_S_IDR3=0                |                                    |
+---------------------------------------------------+------------------------------------+
| - cluster0.has_branch_target_exception=1          | Implements FEAT_BTI.               |
| - cluster1.has_branch_target_exception=1          |                                    |
+---------------------------------------------------+------------------------------------+
| - cluster0.has_pointer_authentication=2           | Implements FEAT_PAuth              |
| - cluster1.has_pointer_authentication=2           |                                    |
+---------------------------------------------------+------------------------------------+
| - cluster0.memory_tagging_support_level=2         | Implements FEAT_MTE2               |
| - cluster1.memory_tagging_support_level=2         |                                    |
| - bp.dram_metadata.is_enabled=1                   |                                    |
+---------------------------------------------------+------------------------------------+

Sample FVP command line invocation:

.. code:: shell

    <path-to-fvp-model>/FVP_Base_RevC-2xAEMvA -C pctl.startup=0.0.0.0 \
    -C cluster0.NUM_CORES=4 -C cluster1.NUM_CORES=4 -C bp.secure_memory=1 \
    -C bp.secureflashloader.fname=trusted-firmware-a/build/fvp/debug/bl1.bin \
    -C bp.flashloader0.fname=trusted-firmware-a/build/fvp/debug/fip.bin \
    -C bp.pl011_uart0.out_file=fvp-uart0.log -C bp.pl011_uart1.out_file=fvp-uart1.log \
    -C bp.pl011_uart2.out_file=fvp-uart2.log \
    -C cluster0.has_arm_v8-5=1 -C cluster1.has_arm_v8-5=1 \
    -C cluster0.has_pointer_authentication=2 -C cluster1.has_pointer_authentication=2 \
    -C cluster0.has_branch_target_exception=1 -C cluster1.has_branch_target_exception=1 \
    -C cluster0.memory_tagging_support_level=2 -C cluster1.memory_tagging_support_level=2 \
    -C bp.dram_metadata.is_enabled=1 \
    -C pci.pci_smmuv3.mmu.SMMU_AIDR=2 -C pci.pci_smmuv3.mmu.SMMU_IDR0=0x0046123B \
    -C pci.pci_smmuv3.mmu.SMMU_IDR1=0x00600002 -C pci.pci_smmuv3.mmu.SMMU_IDR3=0x1714 \
    -C pci.pci_smmuv3.mmu.SMMU_IDR5=0xFFFF0472 -C pci.pci_smmuv3.mmu.SMMU_S_IDR1=0xA0000002 \
    -C pci.pci_smmuv3.mmu.SMMU_S_IDR2=0 -C pci.pci_smmuv3.mmu.SMMU_S_IDR3=0

SPMC Configuration
==================

This section details the configuration files required to deploy Hafnium as the SPMC,
along with those required to configure each secure partion.

SPMC Manifest
-------------

This manifest contains the SPMC *attribute* node consumed by the SPMD at boot
time. It implements `[1]`_ (SP manifest at physical FF-A instance) and serves
two different cases:

The SPMC manifest is used by the SPMD to setup the environment required by the
SPMC to run at S-EL2. SPs run at S-EL1 or S-EL0.

.. code:: shell

    attribute {
        spmc_id = <0x8000>;
        maj_ver = <0x1>;
        min_ver = <0x1>;
        exec_state = <0x0>;
        load_address = <0x0 0x6000000>;
        entrypoint = <0x0 0x6000000>;
        binary_size = <0x60000>;
    };

- *spmc_id* defines the endpoint ID value that SPMC can query through
  ``FFA_ID_GET``.
- *maj_ver/min_ver*. SPMD checks provided FF-A version versus its internal
  version and aborts if not matching.
- *exec_state* defines the SPMC execution state (AArch64 or AArch32).
  Notice Hafnium used as a SPMC only supports AArch64.
- *load_address* and *binary_size* are mostly used to verify secondary
  entry points fit into the loaded binary image.
- *entrypoint* defines the cold boot primary core entry point used by
  SPMD (currently matches ``BL32_BASE``) to enter the SPMC.

Other nodes in the manifest are consumed by Hafnium in the secure world.
A sample can be found at `[7]`_:

- The *hypervisor* node describes SPs. *is_ffa_partition* boolean attribute
  indicates a FF-A compliant SP. The *load_address* field specifies the load
  address at which BL2 loaded the SP package.
- The *cpus* node provides the platform topology and allows MPIDR to VMPIDR mapping.
  Note the primary core is declared first, then secondary cores are declared
  in reverse order.
- The *memory* nodes provide platform information on the ranges of memory
  available for use by SPs at runtime. These ranges relate to either
  secure or non-secure memory, depending on the *device_type* field.
  If the field specifies "memory" the range is secure, else if it specifies
  "ns-memory" the memory is non-secure. The system integrator must exclude
  the memory used by other components that are not SPs, such as the monitor,
  or the SPMC itself, the OS Kernel/Hypervisor, or other NWd VMs.
  The SPMC  limits the SP's address space such that they can only refer to memory
  inside of those ranges, either by defining memory region nodes in their manifest
  as well as memory starting at the load address until the limit defined by the memory
  size. Thus, the SPMC prevents rogue SPs from tampering with memory from other
  components.

.. code:: shell

	memory@0 {
		device_type = "memory";
		reg = <0x0 0x6000000 0x2000000 0x0 0xff000000 0x1000000>;
	};

	memory@1 {
		device_type = "ns-memory";
		reg = <0x0 0x90010000 0x70000000>;
	};

Above find an example representation of the referred memory description. The
ranges are described in a list of unsigned 32-bit values, in which the first
two addresses relate to the based physical address, followed by the respective
page size. The first secure range defined in the node below has base address
`0x0 0x6000000` and size `0x2000000`; following there is another range with
base address `0x0 0xff000000` and size `0x1000000`.

Secure Partitions Configuration
-------------------------------

SP Manifests
~~~~~~~~~~~~

An SP manifest describes SP attributes as defined in `[1]`_
(partition manifest at virtual FF-A instance) in DTS format. It is
represented as a single file associated with the SP. A sample is
provided by `[5]`_. A binding document is provided by `[6]`_.

Platform topology
~~~~~~~~~~~~~~~~~

The *execution-ctx-count* SP manifest field can take the value of one or the
total number of PEs. The FF-A specification `[1]`_  recommends the
following SP types:

- Pinned MP SPs: an execution context matches a physical PE. MP SPs must
  implement the same number of ECs as the number of PEs in the platform.
- Migratable UP SPs: a single execution context can run and be migrated on any
  physical PE. Such SP declares a single EC in its SP manifest. An UP SP can
  receive a direct message request originating from any physical core targeting
  the single execution context.

Secure Partition packages
~~~~~~~~~~~~~~~~~~~~~~~~~

Secure partitions are bundled as independent package files consisting
of:

- a header
- a DTB
- an image payload

The header starts with a magic value and offset values to SP DTB and
image payload. Each SP package is loaded independently by BL2 loader
and verified for authenticity and integrity.

The SP package identified by its UUID (matching FF-A uuid property) is
inserted as a single entry into the FIP at end of the TF-A build flow
as shown:

.. code:: shell

    Trusted Boot Firmware BL2: offset=0x1F0, size=0x8AE1, cmdline="--tb-fw"
    EL3 Runtime Firmware BL31: offset=0x8CD1, size=0x13000, cmdline="--soc-fw"
    Secure Payload BL32 (Trusted OS): offset=0x1BCD1, size=0x15270, cmdline="--tos-fw"
    Non-Trusted Firmware BL33: offset=0x30F41, size=0x92E0, cmdline="--nt-fw"
    HW_CONFIG: offset=0x3A221, size=0x2348, cmdline="--hw-config"
    TB_FW_CONFIG: offset=0x3C569, size=0x37A, cmdline="--tb-fw-config"
    SOC_FW_CONFIG: offset=0x3C8E3, size=0x48, cmdline="--soc-fw-config"
    TOS_FW_CONFIG: offset=0x3C92B, size=0x427, cmdline="--tos-fw-config"
    NT_FW_CONFIG: offset=0x3CD52, size=0x48, cmdline="--nt-fw-config"
    B4B5671E-4A90-4FE1-B81F-FB13DAE1DACB: offset=0x3CD9A, size=0xC168, cmdline="--blob"
    D1582309-F023-47B9-827C-4464F5578FC8: offset=0x48F02, size=0xC168, cmdline="--blob"

.. uml:: ../resources/diagrams/plantuml/fip-secure-partitions.puml

Secure Partitions Layout File
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A json-formatted description file is passed to the build flow specifying paths
to the SP binary image and associated DTS partition manifest file. The latter
is processed by the dtc compiler to generate a DTB fed into the SP package.
Each partition can be configured with the following fields:

:code:`image`
  - Specifies the filename and offset of the image within the SP package.
  - Can be written as :code:`"image": { "file": "path", "offset": 0x1234 }` to
    give both :code:`image.file` and :code:`image.offset` values explicitly, or
    can be written as :code:`"image": "path"` to give :code:`image.file` and value
    and leave :code:`image.offset` absent.

  :code:`image.file`
    - Specifies the filename of the image.

  :code:`image.offset`
    - Specifies the offset of the image within the SP package.
    - Must be 4KB aligned, because that is the translation granule supported by Hafnium SPMC.
    - Optional. Defaults to :code:`0x4000`.

:code:`pm`
  - Specifies the filename and offset of the partition manifest within the SP package.
  - Can be written as :code:`"pm": { "file": "path", "offset": 0x1234 }` to
    give both :code:`pm.file` and :code:`pm.offset` values explicitly, or
    can be written as :code:`"pm": "path"` to give :code:`pm.file` and value
    and leave :code:`pm.offset` absent.

  :code:`pm.file`
    - Specifies the filename of the partition manifest.

  :code:`pm.offset`
    - Specifies the offset of the partition manifest within the SP package.
    - Must be 4KB aligned, because that is the translation granule supported by Hafnium SPMC.
    - Optional. Defaults to :code:`0x1000`.

:code:`image.offset` and :code:`pm.offset` can be leveraged to support SPs with
S1 translation granules that differ from 4KB, and to configure the regions
allocated within the SP package, as well as to comply with the requirements for
the implementation of the boot information protocol (see `Passing boot data to
the SP`_ for more details).

:code:`owner`
  - Specifies the SP owner, identifying the signing domain in case of dual root CoT.
  - Possible values are :code:`SiP` (silicon owner) or :code:`Plat` (platform owner).
  - Optional. Defaults to :code:`SiP`.

:code:`uuid`
  - Specifies the UUID of the partition.
  - Optional. Defaults to the value of the :code:`uuid` field from the DTS partition manifest.

:code:`physical-load-address`
  - Specifies the :code:`load_address` field of the generated DTS fragment.
  - Optional. Defaults to the value of the :code:`load-address` from the DTS partition manifest.

.. code:: shell

    {
        "tee1" : {
            "image": "tee1.bin",
             "pm": "tee1.dts",
             "owner": "SiP",
             "uuid": "1b1820fe-48f7-4175-8999-d51da00b7c9f"
        },

        "tee2" : {
            "image": "tee2.bin",
            "pm": "tee2.dts",
            "owner": "Plat"
        },

        "tee3" : {
            "image": {
                "file": "tee3.bin",
                "offset":"0x2000"
             },
            "pm": {
                "file": "tee3.dts",
                "offset":"0x6000"
             },
            "owner": "Plat"
        },
    }

SPMC boot
=========

The SPMC is loaded by BL2 as the BL32 image.

The SPMC manifest is loaded by BL2 as the ``TOS_FW_CONFIG`` image `[9]`_.

BL2 passes the SPMC manifest address to BL31 through a register.

At boot time, the SPMD in BL31 runs from the primary core, initializes the core
contexts and launches the SPMC (BL32) passing the following information through
registers:

- X0 holds the ``TOS_FW_CONFIG`` physical address (or SPMC manifest blob).
- X1 holds the ``HW_CONFIG`` physical address.
- X4 holds the currently running core linear id.

Secure boot
-----------

The SP content certificate is inserted as a separate FIP item so that BL2 loads SPMC,
SPMC manifest, secure partitions and verifies them for authenticity and integrity.
Refer to TBBR specification `[3]`_.

The multiple-signing domain feature (in current state dual signing domain `[8]`_) allows
the use of two root keys namely S-ROTPK and NS-ROTPK:

- SPMC (BL32) and SPMC manifest are signed by the SiP using the S-ROTPK.
- BL33 may be signed by the OEM using NS-ROTPK.
- An SP may be signed either by SiP (using S-ROTPK) or by OEM (using NS-ROTPK).
- A maximum of 4 partitions can be signed with the S-ROTPK key and 4 partitions
  signed with the NS-ROTPK key.

Also refer to `Secure Partitions Configuration`_ and `TF-A build options`_ sections.

Boot phases
-----------

Primary core boot-up
~~~~~~~~~~~~~~~~~~~~

Upon boot-up, BL31 hands over to the SPMC (BL32) on the primary boot physical
core. The SPMC performs its platform initializations and registers the SPMC
secondary physical core entry point physical address by the use of the
`FFA_SECONDARY_EP_REGISTER`_ interface (SMC invocation from the SPMC to the SPMD
at secure physical FF-A instance).

The SPMC then creates secure partitions base on SP packages and manifests. Each
secure partition is launched in sequence (`SP Boot order`_) on their "primary"
execution context. If the primary boot physical core linear id is N, an MP SP is
started using EC[N] on PE[N] (see `Platform topology`_). If the partition is a
UP SP, it is started using its unique EC0 on PE[N].

The SP primary EC (or the EC used when the partition is booted as described
above):

- Performs the overall SP boot time initialization, and in case of a MP SP,
  prepares the SP environment for other execution contexts.
- In the case of a MP SP, it invokes the FFA_SECONDARY_EP_REGISTER at secure
  virtual FF-A instance (SMC invocation from SP to SPMC) to provide the IPA
  entry point for other execution contexts.
- Exits through ``FFA_MSG_WAIT`` to indicate successful initialization or
  ``FFA_ERROR`` in case of failure.

Secondary cores boot-up
~~~~~~~~~~~~~~~~~~~~~~~

Once the system is started and NWd brought up, a secondary physical core is
woken up by the ``PSCI_CPU_ON`` service invocation. The TF-A SPD hook mechanism
calls into the SPMD on the newly woken up physical core. Then the SPMC is
entered at the secondary physical core entry point.

In the current implementation, the first SP is resumed on the coresponding EC
(the virtual CPU which matches the physical core). The implication is that the
first SP must be a MP SP.

In a linux based system, once secure and normal worlds are booted but prior to
a NWd FF-A driver has been loaded:

- The first SP has initialized all its ECs in response to primary core boot up
  (at system initialization) and secondary core boot up (as a result of linux
  invoking PSCI_CPU_ON for all secondary cores).
- Other SPs have their first execution context initialized as a result of secure
  world initialization on the primary boot core. Other ECs for those SPs have to
  be run first through ffa_run to complete their initialization (which results
  in the EC completing with FFA_MSG_WAIT).

Refer to `Power management`_ for further details.

Loading of SPs
--------------

At boot time, BL2 loads SPs sequentially in addition to the SPMC as depicted
below:

.. uml:: ../resources/diagrams/plantuml/bl2-loading-sp.puml

Note this boot flow is an implementation sample on Arm's FVP platform.
Platforms not using TF-A's *Firmware CONFiguration* framework would adjust to a
different boot flow. The flow restricts to a maximum of 8 secure partitions.

SP Boot order
~~~~~~~~~~~~~

SP manifests provide an optional boot order attribute meant to resolve
dependencies such as an SP providing a service required to properly boot
another SP. SPMC boots the SPs in accordance to the boot order attribute,
lowest to the highest value. If the boot order attribute is absent from the FF-A
manifest, the SP is treated as if it had the highest boot order value
(i.e. lowest booting priority). The FF-A specification mandates this field
is unique to each SP.

It is possible for an SP to call into another SP through a direct request
provided the latter SP has already been booted.

Passing boot data to the SP
~~~~~~~~~~~~~~~~~~~~~~~~~~~

In `[1]`_ , the section  "Boot information protocol" defines a method for passing
data to the SPs at boot time. It specifies the format for the boot information
descriptor and boot information header structures, which describe the data to be
exchanged between SPMC and SP.
The specification also defines the types of data that can be passed.
The aggregate of both the boot info structures and the data itself is designated
the boot information blob, and is passed to a Partition as a contiguous memory
region.

Currently, the SPM implementation supports the FDT type which is used to pass the
partition's DTB manifest.

The region for the boot information blob is allocated through the SP package.

.. image:: ../resources/diagrams/partition-package.png

To adjust the space allocated for the boot information blob, the json description
of the SP (see section `Secure Partitions Layout File`_) shall be updated to contain
the manifest offset. If no offset is provided the manifest offset defaults to 0x1000,
which is the page size in the Hafnium SPMC.

The configuration of the boot protocol is done in the SPs manifest. As defined by
the specification, the manifest field 'gp-register-num' configures the GP register
which shall be used to pass the address to the partitions boot information blob when
booting the partition.
In addition, the Hafnium SPMC implementation requires the boot information arguments
to be listed in a designated DT node:

.. code:: shell

  boot-info {
      compatible = "arm,ffa-manifest-boot-info";
      ffa_manifest;
  };

The whole secure partition package image (see `Secure Partition packages`_) is
mapped to the SP secure EL1&0 Stage-2 translation regime. As such, the SP can
retrieve the address for the boot information blob in the designated GP register,
process the boot information header and descriptors, access its own manifest
DTB blob and extract its partition manifest properties.

SPMC Runtime
============

Parsing SP partition manifests
------------------------------

Hafnium consumes SP manifests as defined in `[1]`_ and `SP manifests`_.
Note the current implementation may not implement all optional fields.

The SP manifest may contain memory and device regions nodes:

- Memory regions are mapped in the SP EL1&0 Stage-2 translation regime at
  load time (or EL1&0 Stage-1 for an S-EL1 SPMC). A memory region node can
  specify RX/TX buffer regions in which case it is not necessary for an SP
  to explicitly invoke the ``FFA_RXTX_MAP`` interface. The memory referred
  shall be contained within the memory ranges defined in SPMC manifest. The
  NS bit in the attributes field should be consistent with the security
  state of the range that it relates to. I.e. non-secure memory shall be
  part of a non-secure memory range, and secure memory shall be contained
  in a secure memory range of a given platform.
- Device regions are mapped in the SP EL1&0 Stage-2 translation regime (or
  EL1&0 Stage-1 for an S-EL1 SPMC) as peripherals and possibly allocate
  additional resources (e.g. interrupts).

For the SPMC, base addresses for memory and device region nodes are IPAs provided
the SPMC identity maps IPAs to PAs within SP EL1&0 Stage-2 translation regime.

Note: in the current implementation both VTTBR_EL2 and VSTTBR_EL2 point to the
same set of page tables. It is still open whether two sets of page tables shall
be provided per SP. The memory region node as defined in the specification
provides a memory security attribute hinting to map either to the secure or
non-secure EL1&0 Stage-2 table if it exists.

Secure partitions scheduling
----------------------------

The FF-A specification `[1]`_ provides two ways to allocate CPU cycles to
secure partitions. For this a VM (Hypervisor or OS kernel), or SP invokes one of:

- the FFA_MSG_SEND_DIRECT_REQ interface.
- the FFA_RUN interface.

Additionally a secure interrupt can pre-empt the normal world execution and give
CPU cycles by transitioning to EL3 and S-EL2.

Mandatory interfaces
--------------------

The following interfaces are exposed to SPs:

-  ``FFA_VERSION``
-  ``FFA_FEATURES``
-  ``FFA_RX_RELEASE``
-  ``FFA_RXTX_MAP``
-  ``FFA_RXTX_UNMAP``
-  ``FFA_PARTITION_INFO_GET``
-  ``FFA_ID_GET``
-  ``FFA_MSG_WAIT``
-  ``FFA_MSG_SEND_DIRECT_REQ``
-  ``FFA_MSG_SEND_DIRECT_RESP``
-  ``FFA_MEM_DONATE``
-  ``FFA_MEM_LEND``
-  ``FFA_MEM_SHARE``
-  ``FFA_MEM_RETRIEVE_REQ``
-  ``FFA_MEM_RETRIEVE_RESP``
-  ``FFA_MEM_RELINQUISH``
-  ``FFA_MEM_FRAG_RX``
-  ``FFA_MEM_FRAG_TX``
-  ``FFA_MEM_RECLAIM``
-  ``FFA_RUN``

As part of the FF-A v1.1 support, the following interfaces were added:

 - ``FFA_NOTIFICATION_BITMAP_CREATE``
 - ``FFA_NOTIFICATION_BITMAP_DESTROY``
 - ``FFA_NOTIFICATION_BIND``
 - ``FFA_NOTIFICATION_UNBIND``
 - ``FFA_NOTIFICATION_SET``
 - ``FFA_NOTIFICATION_GET``
 - ``FFA_NOTIFICATION_INFO_GET``
 - ``FFA_SPM_ID_GET``
 - ``FFA_SECONDARY_EP_REGISTER``
 - ``FFA_MEM_PERM_GET``
 - ``FFA_MEM_PERM_SET``
 - ``FFA_MSG_SEND2``
 - ``FFA_RX_ACQUIRE``

As part of the FF-A v1.2 support, the following interfaces were added:
- ``FFA_PARTITION_INFO_GET_REGS``

FFA_VERSION
~~~~~~~~~~~

``FFA_VERSION`` requires a *requested_version* parameter from the caller.
The returned value depends on the caller:

- Hypervisor or OS kernel in NS-EL1/EL2: the SPMD returns the SPMC version
  specified in the SPMC manifest.
- SP: the SPMC returns its own implemented version.
- SPMC at S-EL1/S-EL2: the SPMD returns its own implemented version.

FFA_FEATURES
~~~~~~~~~~~~

FF-A features supported by the SPMC may be discovered by secure partitions at
boot (that is prior to NWd is booted) or run-time.

The SPMC calling FFA_FEATURES at secure physical FF-A instance always get
FFA_SUCCESS from the SPMD.

The request made by an Hypervisor or OS kernel is forwarded to the SPMC and
the response relayed back to the NWd.

FFA_RXTX_MAP/FFA_RXTX_UNMAP
~~~~~~~~~~~~~~~~~~~~~~~~~~~

When invoked from a secure partition FFA_RXTX_MAP maps the provided send and
receive buffers described by their IPAs to the SP EL1&0 Stage-2 translation
regime as secure buffers in the MMU descriptors.

When invoked from the Hypervisor or OS kernel, the buffers are mapped into the
SPMC EL2 Stage-1 translation regime and marked as NS buffers in the MMU
descriptors. The provided addresses may be owned by a VM in the normal world,
which is expected to receive messages from the secure world. The SPMC will in
this case allocate internal state structures to facilitate RX buffer access
synchronization (through FFA_RX_ACQUIRE interface), and to permit SPs to send
messages.

The FFA_RXTX_UNMAP unmaps the RX/TX pair from the translation regime of the
caller, either it being the Hypervisor or OS kernel, as well as a secure
partition.

FFA_PARTITION_INFO_GET
~~~~~~~~~~~~~~~~~~~~~~

Partition info get call can originate:

- from SP to SPMC
- from Hypervisor or OS kernel to SPMC. The request is relayed by the SPMD.

FFA_PARTITION_INFO_GET_REGS
~~~~~~~~~~~~~~~~~~~~~~~~~~~

This call can originate:

- from SP to SPMC
- from SPMC to SPMD
- from Hypervsior or OS kernel to SPMC. The request is relayed by the SPMD.

The primary use of this ABI is to return partition information via registers
as opposed to via RX/TX buffers and is useful in cases where sharing memory is
difficult.

FFA_ID_GET
~~~~~~~~~~

The FF-A id space is split into a non-secure space and secure space:

- FF-A ID with bit 15 clear relates to VMs.
- FF-A ID with bit 15 set related to SPs.
- FF-A IDs 0, 0xffff, 0x8000 are assigned respectively to the Hypervisor, SPMD
  and SPMC.

The SPMD returns:

- The default zero value on invocation from the Hypervisor.
- The ``spmc_id`` value specified in the SPMC manifest on invocation from
  the SPMC (see `SPMC manifest`_)

This convention helps the SPMC to determine the origin and destination worlds in
an FF-A ABI invocation. In particular the SPMC shall filter unauthorized
transactions in its world switch routine. It must not be permitted for a VM to
use a secure FF-A ID as origin world by spoofing:

- A VM-to-SP direct request/response shall set the origin world to be non-secure
  (FF-A ID bit 15 clear) and destination world to be secure (FF-A ID bit 15
  set).
- Similarly, an SP-to-SP direct request/response shall set the FF-A ID bit 15
  for both origin and destination IDs.

An incoming direct message request arriving at SPMD from NWd is forwarded to
SPMC without a specific check. The SPMC is resumed through eret and "knows" the
message is coming from normal world in this specific code path. Thus the origin
endpoint ID must be checked by SPMC for being a normal world ID.

An SP sending a direct message request must have bit 15 set in its origin
endpoint ID and this can be checked by the SPMC when the SP invokes the ABI.

The SPMC shall reject the direct message if the claimed world in origin endpoint
ID is not consistent:

-  It is either forwarded by SPMD and thus origin endpoint ID must be a "normal
   world ID",
-  or initiated by an SP and thus origin endpoint ID must be a "secure world ID".


FFA_MSG_SEND_DIRECT_REQ/FFA_MSG_SEND_DIRECT_RESP
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a mandatory interface for secure partitions consisting in direct request
and responses with the following rules:

- An SP can send a direct request to another SP.
- An SP can receive a direct request from another SP.
- An SP can send a direct response to another SP.
- An SP cannot send a direct request to an Hypervisor or OS kernel.
- An Hypervisor or OS kernel can send a direct request to an SP.
- An SP can send a direct response to an Hypervisor or OS kernel.

FFA_NOTIFICATION_BITMAP_CREATE/FFA_NOTIFICATION_BITMAP_DESTROY
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The secure partitions notifications bitmap are statically allocated by the SPMC.
Hence, this interface is not to be issued by secure partitions.

At initialization, the SPMC is not aware of VMs/partitions deployed in the
normal world. Hence, the Hypervisor or OS kernel must use both ABIs for SPMC
to be prepared to handle notifications for the provided VM ID.

FFA_NOTIFICATION_BIND/FFA_NOTIFICATION_UNBIND
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Pair of interfaces to manage permissions to signal notifications. Prior to
handling notifications, an FF-A endpoint must allow a given sender to signal a
bitmap of notifications.

If the receiver doesn't have notification support enabled in its FF-A manifest,
it won't be able to bind notifications, hence forbidding it to receive any
notifications.

FFA_NOTIFICATION_SET/FFA_NOTIFICATION_GET
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FFA_NOTIFICATION_GET retrieves all pending global notifications and
per-vCPU notifications targeted to the current vCPU.

Hafnium maintains a global count of pending notifications which gets incremented
and decremented when handling FFA_NOTIFICATION_SET and FFA_NOTIFICATION_GET
respectively. A delayed SRI is triggered if the counter is non-zero when the
SPMC returns to normal world.

FFA_NOTIFICATION_INFO_GET
~~~~~~~~~~~~~~~~~~~~~~~~~

Hafnium maintains a global count of pending notifications whose information
has been retrieved by this interface. The count is incremented and decremented
when handling FFA_NOTIFICATION_INFO_GET and FFA_NOTIFICATION_GET respectively.
It also tracks notifications whose information has been retrieved individually,
such that it avoids duplicating returned information for subsequent calls to
FFA_NOTIFICATION_INFO_GET. For each notification, this state information is
reset when receiver called FFA_NOTIFICATION_GET to retrieve them.

FFA_SPM_ID_GET
~~~~~~~~~~~~~~

Returns the FF-A ID allocated to an SPM component which can be one of SPMD
or SPMC.

At initialization, the SPMC queries the SPMD for the SPMC ID, using the
FFA_ID_GET interface, and records it. The SPMC can also query the SPMD ID using
the FFA_SPM_ID_GET interface at the secure physical FF-A instance.

Secure partitions call this interface at the virtual FF-A instance, to which
the SPMC returns the priorly retrieved SPMC ID.

The Hypervisor or OS kernel can issue the FFA_SPM_ID_GET call handled by the
SPMD, which returns the SPMC ID.

FFA_SECONDARY_EP_REGISTER
~~~~~~~~~~~~~~~~~~~~~~~~~

When the SPMC boots, all secure partitions are initialized on their primary
Execution Context.

The FFA_SECONDARY_EP_REGISTER interface is to be used by a secure partition
from its first execution context, to provide the entry point address for
secondary execution contexts.

A secondary EC is first resumed either upon invocation of PSCI_CPU_ON from
the NWd or by invocation of FFA_RUN.

FFA_RX_ACQUIRE/FFA_RX_RELEASE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The RX buffers can be used to pass information to an FF-A endpoint in the
following scenarios:

 - When it was targetted by a FFA_MSG_SEND2 invokation from another endpoint.
 - Return the result of calling ``FFA_PARTITION_INFO_GET``.
 - In a memory share operation, as part of the ``FFA_MEM_RETRIEVE_RESP``,
   with the memory descriptor of the shared memory.

If a normal world VM is expected to exchange messages with secure world,
its RX/TX buffer addresses are forwarded to the SPMC via FFA_RXTX_MAP ABI,
and are from this moment owned by the SPMC.
The hypervisor must call the FFA_RX_ACQUIRE interface before attempting
to use the RX buffer, in any of the aforementioned scenarios. A successful
call to FFA_RX_ACQUIRE transfers ownership of RX buffer to hypervisor, such
that it can be safely used.

The FFA_RX_RELEASE interface is used after the FF-A endpoint is done with
processing the data received in its RX buffer. If the RX buffer has been
acquired by the hypervisor, the FFA_RX_RELEASE call must be forwarded to
the SPMC to reestablish SPMC's RX ownership.

An attempt from an SP to send a message to a normal world VM whose RX buffer
was acquired by the hypervisor fails with error code FFA_BUSY, to preserve
the RX buffer integrity.
The operation could then be conducted after FFA_RX_RELEASE.

FFA_MSG_SEND2
~~~~~~~~~~~~~

Hafnium copies a message from the sender TX buffer into receiver's RX buffer.
For messages from SPs to VMs, operation is only possible if the SPMC owns
the receiver's RX buffer.

Both receiver and sender need to enable support for indirect messaging,
in their respective partition manifest. The discovery of support
of such feature can be done via FFA_PARTITION_INFO_GET.

On a successful message send, Hafnium pends an RX buffer full framework
notification for the receiver, to inform it about a message in the RX buffer.

The handling of framework notifications is similar to that of
global notifications. Binding of these is not necessary, as these are
reserved to be used by the hypervisor or SPMC.

Paravirtualized interfaces
--------------------------

Hafnium SPMC implements the following implementation-defined interface(s):

HF_INTERRUPT_ENABLE
~~~~~~~~~~~~~~~~~~~

Enables or disables the given virtual interrupt for the calling execution
context. Returns 0 on success, or -1 if the interrupt id is invalid.

HF_INTERRUPT_GET
~~~~~~~~~~~~~~~~

Returns the ID of the next pending virtual interrupt for the calling execution
context, and acknowledges it (i.e. marks it as no longer pending). Returns
HF_INVALID_INTID if there are no pending interrupts.

HF_INTERRUPT_DEACTIVATE
~~~~~~~~~~~~~~~~~~~~~~~

Drops the current interrupt priority and deactivates the given virtual and
physical interrupt ID for the calling execution context. Returns 0 on success,
or -1 otherwise.

HF_INTERRUPT_RECONFIGURE
~~~~~~~~~~~~~~~~~~~~~~~~

An SP specifies the list of interrupts it owns through its partition manifest.
This paravirtualized interface allows an SP to reconfigure a physical interrupt
in runtime. It accepts three arguments, namely, interrupt ID, command and value.
The command & value pair signify what change is being requested by the current
Secure Partition for the given interrupt.

SPMC returns 0 to indicate that the command was processed successfully or -1 if
it failed to do so. At present, this interface only supports the following
commands:

 - ``INT_RECONFIGURE_TARGET_PE``
     - Change the target CPU of the interrupt.
     - Value represents linear CPU index in the range 0 to (MAX_CPUS - 1).

 - ``INT_RECONFIGURE_SEC_STATE``
     - Change the security state of the interrupt.
     - Value must be either 0 (Non-secure) or 1 (Secure).

 - ``INT_RECONFIGURE_ENABLE``
     - Enable or disable the physical interrupt.
     - Value must be either 0 (Disable) or 1 (Enable).

SPMC-SPMD direct requests/responses
-----------------------------------

Implementation-defined FF-A IDs are allocated to the SPMC and SPMD.
Using those IDs in source/destination fields of a direct request/response
permits SPMD to SPMC communication and either way.

- SPMC to SPMD direct request/response uses SMC conduit.
- SPMD to SPMC direct request/response uses ERET conduit.

This is used in particular to convey power management messages.

Notifications
-------------

The FF-A v1.1 specification `[1]`_ defines notifications as an asynchronous
communication mechanism with non-blocking semantics. It allows for one FF-A
endpoint to signal another for service provision, without hindering its current
progress.

Hafnium currently supports 64 notifications. The IDs of each notification define
a position in a 64-bit bitmap.

The signaling of notifications can interchangeably happen between NWd and SWd
FF-A endpoints.

The SPMC is in charge of managing notifications from SPs to SPs, from SPs to
VMs, and from VMs to SPs. An hypervisor component would only manage
notifications from VMs to VMs. Given the SPMC has no visibility of the endpoints
deployed in NWd, the Hypervisor or OS kernel must invoke the interface
FFA_NOTIFICATION_BITMAP_CREATE to allocate the notifications bitmap per FF-A
endpoint in the NWd that supports it.

A sender can signal notifications once the receiver has provided it with
permissions. Permissions are provided by invoking the interface
FFA_NOTIFICATION_BIND.

Notifications are signaled by invoking FFA_NOTIFICATION_SET. Henceforth
they are considered to be in a pending sate. The receiver can retrieve its
pending notifications invoking FFA_NOTIFICATION_GET, which, from that moment,
are considered to be handled.

Per the FF-A v1.1 spec, each FF-A endpoint must be associated with a scheduler
that is in charge of donating CPU cycles for notifications handling. The
FF-A driver calls FFA_NOTIFICATION_INFO_GET to retrieve the information about
which FF-A endpoints have pending notifications. The receiver scheduler is
called and informed by the FF-A driver, and it should allocate CPU cycles to the
receiver.

There are two types of notifications supported:

- Global, which are targeted to a FF-A endpoint and can be handled within any of
  its execution contexts, as determined by the scheduler of the system.
- Per-vCPU, which are targeted to a FF-A endpoint and to be handled within a
  a specific execution context, as determined by the sender.

The type of a notification is set when invoking FFA_NOTIFICATION_BIND to give
permissions to the sender.

Notification signaling resorts to two interrupts:

- Schedule Receiver Interrupt: non-secure physical interrupt to be handled by
  the FF-A driver within the receiver scheduler. At initialization the SPMC
  donates an SGI ID chosen from the secure SGI IDs range and configures it as
  non-secure. The SPMC triggers this SGI on the currently running core when
  there are pending notifications, and the respective receivers need CPU cycles
  to handle them.
- Notifications Pending Interrupt: virtual interrupt to be handled by the
  receiver of the notification. Set when there are pending notifications for the
  given secure partition. The NPI is pended when the NWd relinquishes CPU cycles
  to an SP.

The notifications receipt support is enabled in the partition FF-A manifest.

Memory Sharing
--------------

Hafnium implements the following memory sharing interfaces:

 - ``FFA_MEM_SHARE`` - for shared access between lender and borrower.
 - ``FFA_MEM_LEND`` - borrower to obtain exclusive access, though lender
   retains ownership of the memory.
 - ``FFA_MEM_DONATE`` - lender permanently relinquishes ownership of memory
   to the borrower.

The ``FFA_MEM_RETRIEVE_REQ`` interface is for the borrower to request the
memory to be mapped into its address space: for S-EL1 partitions the SPM updates
their stage 2 translation regime; for S-EL0 partitions the SPM updates their
stage 1 translation regime. On a successful call, the SPMC responds back with
``FFA_MEM_RETRIEVE_RESP``.

The ``FFA_MEM_RELINQUISH`` interface is for when the borrower is done with using
a memory region.

The ``FFA_MEM_RECLAIM`` interface is for the owner of the memory to reestablish
its ownership and exclusive access to the memory shared.

The memory transaction descriptors are transmitted via RX/TX buffers. In
situations where the size of the memory transaction descriptor exceeds the
size of the RX/TX buffers, Hafnium provides support for fragmented transmission
of the full transaction descriptor. The ``FFA_MEM_FRAG_RX`` and ``FFA_MEM_FRAG_TX``
interfaces are for receiving and transmitting the next fragment, respectively.

If lender and borrower(s) are SPs, all memory sharing operations are supported.

Hafnium also supports memory sharing operations between the normal world and the
secure world. If there is an SP involved, the SPMC allocates data to track the
state of the operation.

The SPMC is also the designated allocator for the memory handle. The hypervisor
or OS kernel has the possibility to rely on the SPMC to maintain the state
of the operation, thus saving memory.
An SP can not share, lend or donate memory to the NWd.

The SPMC supports the hypervisor retrieve request, as defined by the FF-A
v1.1 EAC0 specification, in section 16.4.3. The intent is to aid with operations
that the hypervisor must do for a VM retriever. For example, when handling
an FFA_MEM_RECLAIM, if the hypervisor relies on SPMC to keep the state
of the operation, the hypervisor retrieve request can be used to obtain
that state information, do the necessary validations, and update stage 2
memory translation.

Hafnium also supports memory lend and share targetting multiple borrowers.
This is the case for a lender SP to multiple SPs, and for a lender VM to
multiple endpoints (from both secure world and normal world). If there is
at least one borrower VM, the hypervisor is in charge of managing its
stage 2 translation on a successful memory retrieve.
The semantics of ``FFA_MEM_DONATE`` implies ownership transmission,
which should target only one partition.

The memory share interfaces are backwards compatible with memory transaction
descriptors from FF-A v1.0. These get translated to FF-A v1.1 descriptors for
Hafnium's internal processing of the operation. If the FF-A version of a
borrower is v1.0, Hafnium provides FF-A v1.0 compliant memory transaction
descriptors on memory retrieve response.

In the section :ref:`SPMC Configuration` there is a mention of non-secure memory
range, that limit the memory region nodes the SP can define. Whatever is left of
the memory region node carve-outs, the SPMC utilizes the memory to create a set of
page tables it associates with the NWd. The memory sharing operations incoming from
the NWd should refer to addresses belonging to these page tables. The intent
is for SPs not to be able to get access to regions they are not intended to access.
This requires special care from the system integrator to configure the memory ranges
correctly, such that any SP can't be given access and interfere with execution of
other components. More information in the :ref:`Threat Model`.

PE MMU configuration
--------------------

With secure virtualization enabled (``HCR_EL2.VM = 1``) and for S-EL1
partitions, two IPA spaces (secure and non-secure) are output from the
secure EL1&0 Stage-1 translation.
The EL1&0 Stage-2 translation hardware is fed by:

- A secure IPA when the SP EL1&0 Stage-1 MMU is disabled.
- One of secure or non-secure IPA when the secure EL1&0 Stage-1 MMU is enabled.

``VTCR_EL2`` and ``VSTCR_EL2`` provide configuration bits for controlling the
NS/S IPA translations. The following controls are set up:
``VSTCR_EL2.SW = 0`` , ``VSTCR_EL2.SA = 0``, ``VTCR_EL2.NSW = 0``,
``VTCR_EL2.NSA = 1``:

- Stage-2 translations for the NS IPA space access the NS PA space.
- Stage-2 translation table walks for the NS IPA space are to the secure PA space.

Secure and non-secure IPA regions (rooted to by ``VTTBR_EL2`` and ``VSTTBR_EL2``)
use the same set of Stage-2 page tables within a SP.

The ``VTCR_EL2/VSTCR_EL2/VTTBR_EL2/VSTTBR_EL2`` virtual address space
configuration is made part of a vCPU context.

For S-EL0 partitions with VHE enabled, a single secure EL2&0 Stage-1 translation
regime is used for both Hafnium and the partition.

Schedule modes and SP Call chains
---------------------------------

An SP execution context is said to be in SPMC scheduled mode if CPU cycles are
allocated to it by SPMC. Correspondingly, an SP execution context is said to be
in Normal world scheduled mode if CPU cycles are allocated by the normal world.

A call chain represents all SPs in a sequence of invocations of a direct message
request. When execution on a PE is in the secure state, only a single call chain
that runs in the Normal World scheduled mode can exist. FF-A v1.1 spec allows
any number of call chains to run in the SPMC scheduled mode but the Hafnium
SPMC restricts the number of call chains in SPMC scheduled mode to only one for
keeping the implementation simple.

Partition runtime models
------------------------

The runtime model of an endpoint describes the transitions permitted for an
execution context between various states. These are the four partition runtime
models supported (refer to `[1]`_ section 7):

  - RTM_FFA_RUN: runtime model presented to an execution context that is
    allocated CPU cycles through FFA_RUN interface.
  - RTM_FFA_DIR_REQ: runtime model presented to an execution context that is
    allocated CPU cycles through FFA_MSG_SEND_DIRECT_REQ interface.
  - RTM_SEC_INTERRUPT: runtime model presented to an execution context that is
    allocated CPU cycles by SPMC to handle a secure interrupt.
  - RTM_SP_INIT: runtime model presented to an execution context that is
    allocated CPU cycles by SPMC to initialize its state.

If an endpoint execution context attempts to make an invalid transition or a
valid transition that could lead to a loop in the call chain, SPMC denies the
transition with the help of above runtime models.

Interrupt management
--------------------

GIC ownership
~~~~~~~~~~~~~

The SPMC owns the GIC configuration. Secure and non-secure interrupts are
trapped at S-EL2. The SPMC manages interrupt resources and allocates interrupt
IDs based on SP manifests. The SPMC acknowledges physical interrupts and injects
virtual interrupts by setting the use of vIRQ/vFIQ bits before resuming a SP.

Abbreviations:

  - NS-Int: A non-secure physical interrupt. It requires a switch to the normal
    world to be handled if it triggers while execution is in secure world.
  - Other S-Int: A secure physical interrupt targeted to an SP different from
    the one that is currently running.
  - Self S-Int: A secure physical interrupt targeted to the SP that is currently
    running.

Non-secure interrupt handling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This section documents the actions supported in SPMC in response to a non-secure
interrupt as per the guidance provided by FF-A v1.1 EAC0 specification.
An SP specifies one of the following actions in its partition manifest:

  - Non-secure interrupt is signaled.
  - Non-secure interrupt is signaled after a managed exit.
  - Non-secure interrupt is queued.

An SP execution context in a call chain could specify a less permissive action
than subsequent SP execution contexts in the same call chain. The less
permissive action takes precedence over the more permissive actions specified
by the subsequent execution contexts. Please refer to FF-A v1.1 EAC0 section
8.3.1 for further explanation.

Secure interrupt handling
~~~~~~~~~~~~~~~~~~~~~~~~~

This section documents the support implemented for secure interrupt handling in
SPMC as per the guidance provided by FF-A v1.1 EAC0 specification.
The following assumptions are made about the system configuration:

  - In the current implementation, S-EL1 SPs are expected to use the para
    virtualized ABIs for interrupt management rather than accessing the virtual
    GIC interface.
  - Unless explicitly stated otherwise, this support is applicable only for
    S-EL1 SPs managed by SPMC.
  - Secure interrupts are configured as G1S or G0 interrupts.
  - All physical interrupts are routed to SPMC when running a secure partition
    execution context.
  - All endpoints with multiple execution contexts have their contexts pinned
    to corresponding CPUs. Hence, a secure virtual interrupt cannot be signaled
    to a target vCPU that is currently running or blocked on a different
    physical CPU.

A physical secure interrupt could trigger while CPU is executing in normal world
or secure world.
The action of SPMC for a secure interrupt depends on: the state of the target
execution context of the SP that is responsible for handling the interrupt;
whether the interrupt triggered while execution was in normal world or secure
world.

Secure interrupt signaling mechanisms
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signaling refers to the mechanisms used by SPMC to indicate to the SP execution
context that it has a pending virtual interrupt and to further run the SP
execution context, such that it can handle the virtual interrupt. SPMC uses
either the FFA_INTERRUPT interface with ERET conduit or vIRQ signal for signaling
to S-EL1 SPs. When normal world execution is preempted by a secure interrupt,
the SPMD uses the FFA_INTERRUPT ABI with ERET conduit to signal interrupt to SPMC
running in S-EL2.

+-----------+---------+---------------+---------------------------------------+
| SP State  | Conduit | Interface and | Description                           |
|           |         | parameters    |                                       |
+-----------+---------+---------------+---------------------------------------+
| WAITING   | ERET,   | FFA_INTERRUPT,| SPMC signals to SP the ID of pending  |
|           | vIRQ    | Interrupt ID  | interrupt. It pends vIRQ signal and   |
|           |         |               | resumes execution context of SP       |
|           |         |               | through ERET.                         |
+-----------+---------+---------------+---------------------------------------+
| BLOCKED   | ERET,   | FFA_INTERRUPT | SPMC signals to SP that an interrupt  |
|           | vIRQ    |               | is pending. It pends vIRQ signal and  |
|           |         |               | resumes execution context of SP       |
|           |         |               | through ERET.                         |
+-----------+---------+---------------+---------------------------------------+
| PREEMPTED | vIRQ    | NA            | SPMC pends the vIRQ signal but does   |
|           |         |               | not resume execution context of SP.   |
+-----------+---------+---------------+---------------------------------------+
| RUNNING   | ERET,   | NA            | SPMC pends the vIRQ signal and resumes|
|           | vIRQ    |               | execution context of SP through ERET. |
+-----------+---------+---------------+---------------------------------------+

Secure interrupt completion mechanisms
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A SP signals secure interrupt handling completion to the SPMC through the
following mechanisms:

  - ``FFA_MSG_WAIT`` ABI if it was in WAITING state.
  - ``FFA_RUN`` ABI if its was in BLOCKED state.

This is a remnant of SPMC implementation based on the FF-A v1.0 specification.
In the current implementation, S-EL1 SPs use the para-virtualized HVC interface
implemented by SPMC to perform priority drop and interrupt deactivation (SPMC
configures EOImode = 0, i.e. priority drop and deactivation are done together).
The SPMC performs checks to deny the state transition upon invocation of
either FFA_MSG_WAIT or FFA_RUN interface if the SP didn't perform the
deactivation of the secure virtual interrupt.

If the current SP execution context was preempted by a secure interrupt to be
handled by execution context of target SP, SPMC resumes current SP after signal
completion by target SP execution context.

Actions for a secure interrupt triggered while execution is in normal world
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+-------------------+----------+-----------------------------------------------+
| State of target   | Action   | Description                                   |
| execution context |          |                                               |
+-------------------+----------+-----------------------------------------------+
| WAITING           | Signaled | This starts a new call chain in SPMC scheduled|
|                   |          | mode.                                         |
+-------------------+----------+-----------------------------------------------+
| PREEMPTED         | Queued   | The target execution must have been preempted |
|                   |          | by a non-secure interrupt. SPMC queues the    |
|                   |          | secure virtual interrupt now. It is signaled  |
|                   |          | when the target execution context next enters |
|                   |          | the RUNNING state.                            |
+-------------------+----------+-----------------------------------------------+
| BLOCKED, RUNNING  | NA       | The target execution context is blocked or    |
|                   |          | running on a different CPU. This is not       |
|                   |          | supported by current SPMC implementation and  |
|                   |          | execution hits panic.                         |
+-------------------+----------+-----------------------------------------------+

If normal world execution was preempted by a secure interrupt, SPMC uses
FFA_NORMAL_WORLD_RESUME ABI to indicate completion of secure interrupt handling
and further returns execution to normal world.

The following figure describes interrupt handling flow when a secure interrupt
triggers while execution is in normal world:

.. image:: ../resources/diagrams/ffa-secure-interrupt-handling-nwd.png

A brief description of the events:

  - 1) Secure interrupt triggers while normal world is running.
  - 2) FIQ gets trapped to EL3.
  - 3) SPMD signals secure interrupt to SPMC at S-EL2 using FFA_INTERRUPT ABI.
  - 4) SPMC identifies target vCPU of SP and injects virtual interrupt (pends
       vIRQ).
  - 5) Assuming SP1 vCPU is in WAITING state, SPMC signals virtual interrupt
       using FFA_INTERRUPT with interrupt id as an argument and resumes the SP1
       vCPU using ERET in SPMC scheduled mode.
  - 6) Execution traps to vIRQ handler in SP1 provided that the virtual
       interrupt is not masked i.e., PSTATE.I = 0
  - 7) SP1 queries for the pending virtual interrupt id using a paravirtualized
       HVC call. SPMC clears the pending virtual interrupt state management
       and returns the pending virtual interrupt id.
  - 8) SP1 services the virtual interrupt and invokes the paravirtualized
       de-activation HVC call. SPMC de-activates the physical interrupt,
       clears the fields tracking the secure interrupt and resumes SP1 vCPU.
  - 9) SP1 performs secure interrupt completion through FFA_MSG_WAIT ABI.
  - 10) SPMC returns control to EL3 using FFA_NORMAL_WORLD_RESUME.
  - 11) EL3 resumes normal world execution.

Actions for a secure interrupt triggered while execution is in secure world
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+-------------------+----------+------------------------------------------------+
| State of target   | Action   | Description                                    |
| execution context |          |                                                |
+-------------------+----------+------------------------------------------------+
| WAITING           | Signaled | This starts a new call chain in SPMC scheduled |
|                   |          | mode.                                          |
+-------------------+----------+------------------------------------------------+
| PREEMPTED by Self | Signaled | The target execution context reenters the      |
| S-Int             |          | RUNNING state to handle the secure virtual     |
|                   |          | interrupt.                                     |
+-------------------+----------+------------------------------------------------+
| PREEMPTED by      | Queued   | SPMC queues the secure virtual interrupt now.  |
| NS-Int            |          | It is signaled when the target execution       |
|                   |          | context next enters the RUNNING state.         |
+-------------------+----------+------------------------------------------------+
| BLOCKED           | Signaled | Both preempted and target execution contexts   |
|                   |          | must have been part of the Normal world        |
|                   |          | scheduled call chain. Refer scenario 1 of      |
|                   |          | Table 8.4 in the FF-A v1.1 EAC0 spec.          |
+-------------------+----------+------------------------------------------------+
| RUNNING           | NA       | The target execution context is running on a   |
|                   |          | different CPU. This scenario is not supported  |
|                   |          | by current SPMC implementation and execution   |
|                   |          | hits panic.                                    |
+-------------------+----------+------------------------------------------------+

The following figure describes interrupt handling flow when a secure interrupt
triggers while execution is in secure world. We assume OS kernel sends a direct
request message to SP1. Further, SP1 sends a direct request message to SP2. SP1
enters BLOCKED state and SPMC resumes SP2.

.. image:: ../resources/diagrams/ffa-secure-interrupt-handling-swd.png

A brief description of the events:

  - 1) Secure interrupt triggers while SP2 is running.
  - 2) SP2 gets preempted and execution traps to SPMC as IRQ.
  - 3) SPMC finds the target vCPU of secure partition responsible for handling
       this secure interrupt. In this scenario, it is SP1.
  - 4) SPMC pends vIRQ for SP1 and signals through FFA_INTERRUPT interface.
       SPMC further resumes SP1 through ERET conduit. Note that SP1 remains in
       Normal world schedule mode.
  - 6) Execution traps to vIRQ handler in SP1 provided that the virtual
       interrupt is not masked i.e., PSTATE.I = 0
  - 7) SP1 queries for the pending virtual interrupt id using a paravirtualized
       HVC call. SPMC clears the pending virtual interrupt state management
       and returns the pending virtual interrupt id.
  - 8) SP1 services the virtual interrupt and invokes the paravirtualized
       de-activation HVC call. SPMC de-activates the physical interrupt and
       clears the fields tracking the secure interrupt and resumes SP1 vCPU.
  - 9) Since SP1 direct request completed with FFA_INTERRUPT, it resumes the
       direct request to SP2 by invoking FFA_RUN.
  - 9) SPMC resumes the pre-empted vCPU of SP2.

EL3 interrupt handling
~~~~~~~~~~~~~~~~~~~~~~

In GICv3 based systems, EL3 interrupts are configured as Group0 secure
interrupts. Execution traps to SPMC when a Group0 interrupt triggers while an
SP is running. Further, SPMC running at S-EL2 uses FFA_EL3_INTR_HANDLE ABI to
request EL3 platform firmware to handle a pending Group0 interrupt.
Similarly, SPMD registers a handler with interrupt management framework to
delegate handling of Group0 interrupt to the platform if the interrupt triggers
in normal world.

 - Platform hook

   - plat_spmd_handle_group0_interrupt

     SPMD provides platform hook to handle Group0 secure interrupts. In the
     current design, SPMD expects the platform not to delegate handling to the
     NWd (such as through SDEI) while processing Group0 interrupts.

Power management
----------------

In platforms with or without secure virtualization:

- The NWd owns the platform PM policy.
- The Hypervisor or OS kernel is the component initiating PSCI service calls.
- The EL3 PSCI library is in charge of the PM coordination and control
  (eventually writing to platform registers).
- While coordinating PM events, the PSCI library calls backs into the Secure
  Payload Dispatcher for events the latter has statically registered to.

When using the SPMD as a Secure Payload Dispatcher:

- A power management event is relayed through the SPD hook to the SPMC.
- In the current implementation only cpu on (svc_on_finish) and cpu off
  (svc_off) hooks are registered.
- The behavior for the cpu on event is described in `Secondary cores boot-up`_.
  The SPMC is entered through its secondary physical core entry point.
- The cpu off event occurs when the NWd calls PSCI_CPU_OFF. The PM event is
  signaled to the SPMC through a power management framework message.
  It consists in a SPMD-to-SPMC direct request/response (`SPMC-SPMD direct
  requests/responses`_) conveying the event details and SPMC response.
  The SPMD performs a synchronous entry into the SPMC. The SPMC is entered and
  updates its internal state to reflect the physical core is being turned off.
  In the current implementation no SP is resumed as a consequence. This behavior
  ensures a minimal support for CPU hotplug e.g. when initiated by the NWd linux
  userspace.

Arm architecture extensions for security hardening
--------------------------------------------------

Hafnium supports the following architecture extensions for security hardening:

- Pointer authentication (FEAT_PAuth): the extension permits detection of forged
  pointers used by ROP type of attacks through the signing of the pointer
  value. Hafnium is built with the compiler branch protection option to permit
  generation of a pointer authentication code for return addresses (pointer
  authentication for instructions). The APIA key is used while Hafnium runs.
  A random key is generated at boot time and restored upon entry into Hafnium
  at run-time. APIA and other keys (APIB, APDA, APDB, APGA) are saved/restored
  in vCPU contexts permitting to enable pointer authentication in VMs/SPs.
- Branch Target Identification (FEAT_BTI): the extension permits detection of
  unexpected indirect branches used by JOP type of attacks. Hafnium is built
  with the compiler branch protection option, inserting land pads at function
  prologues that are reached by indirect branch instructions (BR/BLR).
  Hafnium code pages are marked as guarded in the EL2 Stage-1 MMU descriptors
  such that an indirect branch must always target a landpad. A fault is
  triggered otherwise. VMs/SPs can (independently) mark their code pages as
  guarded in the EL1&0 Stage-1 translation regime.
- Memory Tagging Extension (FEAT_MTE): the option permits detection of out of
  bound memory array accesses or re-use of an already freed memory region.
  Hafnium enables the compiler option permitting to leverage MTE stack tagging
  applied to core stacks. Core stacks are marked as normal tagged memory in the
  EL2 Stage-1 translation regime. A synchronous data abort is generated upon tag
  check failure on load/stores. A random seed is generated at boot time and
  restored upon entry into Hafnium. MTE system registers are saved/restored in
  vCPU contexts permitting MTE usage from VMs/SPs.

SMMUv3 support in Hafnium
-------------------------

An SMMU is analogous to an MMU in a CPU. It performs address translations for
Direct Memory Access (DMA) requests from system I/O devices.
The responsibilities of an SMMU include:

-  Translation: Incoming DMA requests are translated from bus address space to
   system physical address space using translation tables compliant to
   Armv8/Armv7 VMSA descriptor format.
-  Protection: An I/O device can be prohibited from read, write access to a
   memory region or allowed.
-  Isolation: Traffic from each individial device can be independently managed.
   The devices are differentiated from each other using unique translation
   tables.

The following diagram illustrates a typical SMMU IP integrated in a SoC with
several I/O devices along with Interconnect and Memory system.

.. image:: ../resources/diagrams/MMU-600.png

SMMU has several versions including SMMUv1, SMMUv2 and SMMUv3. Hafnium provides
support for SMMUv3 driver in both normal and secure world. A brief introduction
of SMMUv3 functionality and the corresponding software support in Hafnium is
provided here.

SMMUv3 features
~~~~~~~~~~~~~~~

-  SMMUv3 provides Stage1, Stage2 translation as well as nested (Stage1 + Stage2)
   translation support. It can either bypass or abort incoming translations as
   well.
-  Traffic (memory transactions) from each upstream I/O peripheral device,
   referred to as Stream, can be independently managed using a combination of
   several memory based configuration structures. This allows the SMMUv3 to
   support a large number of streams with each stream assigned to a unique
   translation context.
-  Support for Armv8.1 VMSA where the SMMU shares the translation tables with
   a Processing Element. AArch32(LPAE) and AArch64 translation table format
   are supported by SMMUv3.
-  SMMUv3 offers non-secure stream support with secure stream support being
   optional. Logically, SMMUv3 behaves as if there is an indepdendent SMMU
   instance for secure and non-secure stream support.
-  It also supports sub-streams to differentiate traffic from a virtualized
   peripheral associated with a VM/SP.
-  Additionally, SMMUv3.2 provides support for PEs implementing Armv8.4-A
   extensions. Consequently, SPM depends on Secure EL2 support in SMMUv3.2
   for providing Secure Stage2 translation support to upstream peripheral
   devices.

SMMUv3 Programming Interfaces
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SMMUv3 has three software interfaces that are used by the Hafnium driver to
configure the behaviour of SMMUv3 and manage the streams.

-  Memory based data strutures that provide unique translation context for
   each stream.
-  Memory based circular buffers for command queue and event queue.
-  A large number of SMMU configuration registers that are memory mapped during
   boot time by Hafnium driver. Except a few registers, all configuration
   registers have independent secure and non-secure versions to configure the
   behaviour of SMMUv3 for translation of secure and non-secure streams
   respectively.

Peripheral device manifest
~~~~~~~~~~~~~~~~~~~~~~~~~~

Currently, SMMUv3 driver in Hafnium only supports dependent peripheral devices.
These devices are dependent on PE endpoint to initiate and receive memory
management transactions on their behalf. The acccess to the MMIO regions of
any such device is assigned to the endpoint during boot. Moreover, SMMUv3 driver
uses the same stage 2 translations for the device as those used by partition
manager on behalf of the PE endpoint. This ensures that the peripheral device
has the same visibility of the physical address space as the endpoint. The
device node of the corresponding partition manifest (refer to `[1]`_ section 3.2
) must specify these additional properties for each peripheral device in the
system :

-  smmu-id: This field helps to identify the SMMU instance that this device is
   upstream of.
-  stream-ids: List of stream IDs assigned to this device.

.. code:: shell

    smmuv3-testengine {
        base-address = <0x00000000 0x2bfe0000>;
        pages-count = <32>;
        attributes = <0x3>;
        smmu-id = <0>;
        stream-ids = <0x0 0x1>;
        interrupts = <0x2 0x3>, <0x4 0x5>;
        exclusive-access;
    };

SMMUv3 driver limitations
~~~~~~~~~~~~~~~~~~~~~~~~~

The primary design goal for the Hafnium SMMU driver is to support secure
streams.

-  Currently, the driver only supports Stage2 translations. No support for
   Stage1 or nested translations.
-  Supports only AArch64 translation format.
-  No support for features such as PCI Express (PASIDs, ATS, PRI), MSI, RAS,
   Fault handling, Performance Monitor Extensions, Event Handling, MPAM.
-  No support for independent peripheral devices.

S-EL0 Partition support
-----------------------
The SPMC (Hafnium) has limited capability to run S-EL0 FF-A partitions using
FEAT_VHE (mandatory with ARMv8.1 in non-secure state, and in secure world
with ARMv8.4 and FEAT_SEL2).

S-EL0 partitions are useful for simple partitions that don't require full
Trusted OS functionality. It is also useful to reduce jitter and cycle
stealing from normal world since they are more lightweight than VMs.

S-EL0 partitions are presented, loaded and initialized the same as S-EL1 VMs by
the SPMC. They are differentiated primarily by the 'exception-level' property
and the 'execution-ctx-count' property in the SP manifest. They are host apps
under the single EL2&0 Stage-1 translation regime controlled by the SPMC and
call into the SPMC through SVCs as opposed to HVCs and SMCs. These partitions
can use FF-A defined services (FFA_MEM_PERM_*) to update or change permissions
for memory regions.

S-EL0 partitions are required by the FF-A specification to be UP endpoints,
capable of migrating, and the SPMC enforces this requirement. The SPMC allows
a S-EL0 partition to accept a direct message from secure world and normal world,
and generate direct responses to them.
All S-EL0 partitions must use AArch64. AArch32 S-EL0 partitions are not supported.

Memory sharing, indirect messaging, and notifications functionality with S-EL0
partitions is supported.

Interrupt handling is not supported with S-EL0 partitions and is work in
progress.

References
==========

.. _TF-A project: https://trustedfirmware-a.readthedocs.io/en/latest/

.. _[1]:

[1] `Arm Firmware Framework for Arm A-profile <https://developer.arm.com/docs/den0077/latest>`__

.. _[2]:

[2] `Secure Partition Manager using MM interface <https://trustedfirmware-a.readthedocs.io/en/latest/components/secure-partition-manager-mm.html>`__

.. _[3]:

[3] `Trusted Boot Board Requirements
Client <https://developer.arm.com/documentation/den0006/d/>`__

.. _[4]:

[4] https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/lib/el3_runtime/aarch64/context.S#n45

.. _[5]:

[5] https://git.trustedfirmware.org/TF-A/tf-a-tests.git/tree/spm/cactus/plat/arm/fvp/fdts/cactus.dts

.. _[6]:

[6] https://trustedfirmware-a.readthedocs.io/en/latest/components/ffa-manifest-binding.html

.. _[7]:

[7] https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/tree/plat/arm/board/fvp/fdts/fvp_spmc_manifest.dts

.. _[8]:

[8] https://lists.trustedfirmware.org/archives/list/tf-a@lists.trustedfirmware.org/thread/CFQFGU6H2D5GZYMUYGTGUSXIU3OYZP6U/

.. _[9]:

[9] https://trustedfirmware-a.readthedocs.io/en/latest/design/firmware-design.html#dynamic-configuration-during-cold-boot

.. _[10]:

[10] https://trustedfirmware-a.readthedocs.io/en/latest/getting_started/build-options.html#

--------------

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