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/*
* Copyright (C) 2014, 2015 Intel Corporation; author Matt Fleming
*
* Early support for invoking 32-bit EFI services from a 64-bit kernel.
*
* Because this thunking occurs before ExitBootServices() we have to
* restore the firmware's 32-bit GDT before we make EFI serivce calls,
* since the firmware's 32-bit IDT is still currently installed and it
* needs to be able to service interrupts.
*
* On the plus side, we don't have to worry about mangling 64-bit
* addresses into 32-bits because we're executing with an identify
* mapped pagetable and haven't transitioned to 64-bit virtual addresses
* yet.
*/
#include <linux/linkage.h>
#include <asm/msr.h>
#include <asm/page_types.h>
#include <asm/processor-flags.h>
#include <asm/segment.h>
.code64
.text
ENTRY(efi64_thunk)
push %rbp
push %rbx
subq $8, %rsp
leaq efi_exit32(%rip), %rax
movl %eax, 4(%rsp)
leaq efi_gdt64(%rip), %rax
movl %eax, (%rsp)
movl %eax, 2(%rax) /* Fixup the gdt base address */
movl %ds, %eax
push %rax
movl %es, %eax
push %rax
movl %ss, %eax
push %rax
/*
* Convert x86-64 ABI params to i386 ABI
*/
subq $32, %rsp
movl %esi, 0x0(%rsp)
movl %edx, 0x4(%rsp)
movl %ecx, 0x8(%rsp)
movq %r8, %rsi
movl %esi, 0xc(%rsp)
movq %r9, %rsi
movl %esi, 0x10(%rsp)
sgdt save_gdt(%rip)
leaq 1f(%rip), %rbx
movq %rbx, func_rt_ptr(%rip)
/*
* Switch to gdt with 32-bit segments. This is the firmware GDT
* that was installed when the kernel started executing. This
* pointer was saved at the EFI stub entry point in head_64.S.
*/
leaq efi32_boot_gdt(%rip), %rax
lgdt (%rax)
pushq $__KERNEL_CS
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
1: addq $32, %rsp
lgdt save_gdt(%rip)
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/*
* Convert 32-bit status code into 64-bit.
*/
test %rax, %rax
jz 1f
movl %eax, %ecx
andl $0x0fffffff, %ecx
andl $0xf0000000, %eax
shl $32, %rax
or %rcx, %rax
1:
addq $8, %rsp
pop %rbx
pop %rbp
ret
ENDPROC(efi64_thunk)
ENTRY(efi_exit32)
movq func_rt_ptr(%rip), %rax
push %rax
mov %rdi, %rax
ret
ENDPROC(efi_exit32)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
ENTRY(efi_enter32)
movl $__KERNEL_DS, %eax
movl %eax, %ds
movl %eax, %es
movl %eax, %ss
/* Reload pgtables */
movl %cr3, %eax
movl %eax, %cr3
/* Disable paging */
movl %cr0, %eax
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Disable long mode via EFER */
movl $MSR_EFER, %ecx
rdmsr
btrl $_EFER_LME, %eax
wrmsr
call *%edi
/* We must preserve return value */
movl %eax, %edi
/*
* Some firmware will return with interrupts enabled. Be sure to
* disable them before we switch GDTs.
*/
cli
movl 56(%esp), %eax
movl %eax, 2(%eax)
lgdtl (%eax)
movl %cr4, %eax
btsl $(X86_CR4_PAE_BIT), %eax
movl %eax, %cr4
movl %cr3, %eax
movl %eax, %cr3
movl $MSR_EFER, %ecx
rdmsr
btsl $_EFER_LME, %eax
wrmsr
xorl %eax, %eax
lldt %ax
movl 60(%esp), %eax
pushl $__KERNEL_CS
pushl %eax
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
lret
ENDPROC(efi_enter32)
.data
.balign 8
.global efi32_boot_gdt
efi32_boot_gdt: .word 0
.quad 0
save_gdt: .word 0
.quad 0
func_rt_ptr: .quad 0
.global efi_gdt64
efi_gdt64:
.word efi_gdt64_end - efi_gdt64
.long 0 /* Filled out by user */
.word 0
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x0080890000000000 /* TS descriptor */
.quad 0x0000000000000000 /* TS continued */
efi_gdt64_end:
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