x86: Add support for starting 64-bit kernel
Add code to jump to a 64-bit Linux kernel. We need to set up a flat page
table structure, a new GDT and then go through a few hoops in the right
order.
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/call64.S b/arch/x86/cpu/call64.S
new file mode 100644
index 0000000..74dd5a8
--- /dev/null
+++ b/arch/x86/cpu/call64.S
@@ -0,0 +1,93 @@
+/*
+ * (C) Copyright 2014 Google, Inc
+ * Copyright (C) 1991, 1992, 1993 Linus Torvalds
+ *
+ * Parts of this copied from Linux arch/x86/boot/compressed/head_64.S
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ */
+
+#include <asm/global_data.h>
+#include <asm/msr-index.h>
+#include <asm/processor-flags.h>
+
+.code32
+.globl cpu_call64
+cpu_call64:
+ /*
+ * cpu_call64(ulong pgtable, ulong setup_base, ulong target)
+ *
+ * eax - pgtable
+ * edx - setup_base
+ * ecx - target
+ */
+ cli
+ push %ecx /* arg2 = target */
+ push %edx /* arg1 = setup_base */
+ mov %eax, %ebx
+
+ /* Load new GDT with the 64bit segments using 32bit descriptor */
+ leal gdt, %eax
+ movl %eax, gdt+2
+ lgdt gdt
+
+ /* Enable PAE mode */
+ movl $(X86_CR4_PAE), %eax
+ movl %eax, %cr4
+
+ /* Enable the boot page tables */
+ leal (%ebx), %eax
+ movl %eax, %cr3
+
+ /* Enable Long mode in EFER (Extended Feature Enable Register) */
+ movl $MSR_EFER, %ecx
+ rdmsr
+ btsl $_EFER_LME, %eax
+ wrmsr
+
+ /* After gdt is loaded */
+ xorl %eax, %eax
+ lldt %ax
+ movl $0x20, %eax
+ ltr %ax
+
+ /*
+ * Setup for the jump to 64bit mode
+ *
+ * When the jump is performed we will be in long mode but
+ * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
+ * (and in turn EFER.LMA = 1). To jump into 64bit mode we use
+ * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
+ * We place all of the values on our mini stack so lret can
+ * used to perform that far jump. See the gdt below.
+ */
+ pop %esi /* setup_base */
+
+ pushl $0x10
+ leal lret_target, %eax
+ pushl %eax
+
+ /* Enter paged protected Mode, activating Long Mode */
+ movl $(X86_CR0_PG | X86_CR0_PE), %eax
+ movl %eax, %cr0
+
+ /* Jump from 32bit compatibility mode into 64bit mode. */
+ lret
+
+code64:
+lret_target:
+ pop %eax /* target */
+ mov %eax, %eax /* Clear bits 63:32 */
+ jmp *%eax /* Jump to the 64-bit target */
+
+ .data
+gdt:
+ .word gdt_end - gdt
+ .long gdt
+ .word 0
+ .quad 0x0000000000000000 /* NULL descriptor */
+ .quad 0x00af9a000000ffff /* __KERNEL_CS */
+ .quad 0x00cf92000000ffff /* __KERNEL_DS */
+ .quad 0x0080890000000000 /* TS descriptor */
+ .quad 0x0000000000000000 /* TS continued */
+gdt_end: