v4.19.13 snapshot.
diff --git a/arch/x86/boot/pm.c b/arch/x86/boot/pm.c
new file mode 100644
index 0000000..8062f89
--- /dev/null
+++ b/arch/x86/boot/pm.c
@@ -0,0 +1,126 @@
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ * Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ * This file is part of the Linux kernel, and is made available under
+ * the terms of the GNU General Public License version 2.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Prepare the machine for transition to protected mode.
+ */
+
+#include "boot.h"
+#include <asm/segment.h>
+
+/*
+ * Invoke the realmode switch hook if present; otherwise
+ * disable all interrupts.
+ */
+static void realmode_switch_hook(void)
+{
+ if (boot_params.hdr.realmode_swtch) {
+ asm volatile("lcallw *%0"
+ : : "m" (boot_params.hdr.realmode_swtch)
+ : "eax", "ebx", "ecx", "edx");
+ } else {
+ asm volatile("cli");
+ outb(0x80, 0x70); /* Disable NMI */
+ io_delay();
+ }
+}
+
+/*
+ * Disable all interrupts at the legacy PIC.
+ */
+static void mask_all_interrupts(void)
+{
+ outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */
+ io_delay();
+ outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */
+ io_delay();
+}
+
+/*
+ * Reset IGNNE# if asserted in the FPU.
+ */
+static void reset_coprocessor(void)
+{
+ outb(0, 0xf0);
+ io_delay();
+ outb(0, 0xf1);
+ io_delay();
+}
+
+/*
+ * Set up the GDT
+ */
+
+struct gdt_ptr {
+ u16 len;
+ u32 ptr;
+} __attribute__((packed));
+
+static void setup_gdt(void)
+{
+ /* There are machines which are known to not boot with the GDT
+ being 8-byte unaligned. Intel recommends 16 byte alignment. */
+ static const u64 boot_gdt[] __attribute__((aligned(16))) = {
+ /* CS: code, read/execute, 4 GB, base 0 */
+ [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
+ /* DS: data, read/write, 4 GB, base 0 */
+ [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
+ /* TSS: 32-bit tss, 104 bytes, base 4096 */
+ /* We only have a TSS here to keep Intel VT happy;
+ we don't actually use it for anything. */
+ [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
+ };
+ /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
+ of the gdt_ptr contents. Thus, make it static so it will
+ stay in memory, at least long enough that we switch to the
+ proper kernel GDT. */
+ static struct gdt_ptr gdt;
+
+ gdt.len = sizeof(boot_gdt)-1;
+ gdt.ptr = (u32)&boot_gdt + (ds() << 4);
+
+ asm volatile("lgdtl %0" : : "m" (gdt));
+}
+
+/*
+ * Set up the IDT
+ */
+static void setup_idt(void)
+{
+ static const struct gdt_ptr null_idt = {0, 0};
+ asm volatile("lidtl %0" : : "m" (null_idt));
+}
+
+/*
+ * Actual invocation sequence
+ */
+void go_to_protected_mode(void)
+{
+ /* Hook before leaving real mode, also disables interrupts */
+ realmode_switch_hook();
+
+ /* Enable the A20 gate */
+ if (enable_a20()) {
+ puts("A20 gate not responding, unable to boot...\n");
+ die();
+ }
+
+ /* Reset coprocessor (IGNNE#) */
+ reset_coprocessor();
+
+ /* Mask all interrupts in the PIC */
+ mask_all_interrupts();
+
+ /* Actual transition to protected mode... */
+ setup_idt();
+ setup_gdt();
+ protected_mode_jump(boot_params.hdr.code32_start,
+ (u32)&boot_params + (ds() << 4));
+}