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/* SPDX-License-Identifier: GPL-2.0 */
/*
* 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 identity
* 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
SYM_FUNC_START(__efi64_thunk)
push %rbp
push %rbx
leaq 1f(%rip), %rbp
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)
movl %r8d, 0xc(%rsp)
movl %r9d, 0x10(%rsp)
leaq 0x14(%rsp), %rbx
sgdt (%rbx)
/*
* 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.
*
* Pass the saved DS selector to the 32-bit code, and use far return to
* restore the saved CS selector.
*/
leaq efi32_boot_gdt(%rip), %rax
lgdt (%rax)
movzwl efi32_boot_ds(%rip), %edx
movzwq efi32_boot_cs(%rip), %rax
pushq %rax
leaq efi_enter32(%rip), %rax
pushq %rax
lretq
1: addq $32, %rsp
movq %rdi, %rax
pop %rbx
movl %ebx, %ss
pop %rbx
movl %ebx, %es
pop %rbx
movl %ebx, %ds
/* Clear out 32-bit selector from FS and GS */
xorl %ebx, %ebx
movl %ebx, %fs
movl %ebx, %gs
/*
* Convert 32-bit status code into 64-bit.
*/
roll $1, %eax
rorq $1, %rax
pop %rbx
pop %rbp
ret
SYM_FUNC_END(__efi64_thunk)
.code32
/*
* EFI service pointer must be in %edi.
*
* The stack should represent the 32-bit calling convention.
*/
SYM_FUNC_START_LOCAL(efi_enter32)
/* Load firmware selector into data and stack segment registers */
movl %edx, %ds
movl %edx, %es
movl %edx, %fs
movl %edx, %gs
movl %edx, %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
lgdtl (%ebx)
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
pushl $__KERNEL_CS
pushl %ebp
/* Enable paging */
movl %cr0, %eax
btsl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
lret
SYM_FUNC_END(efi_enter32)
.data
.balign 8
SYM_DATA_START(efi32_boot_gdt)
.word 0
.quad 0
SYM_DATA_END(efi32_boot_gdt)
SYM_DATA_START(efi32_boot_cs)
.word 0
SYM_DATA_END(efi32_boot_cs)
SYM_DATA_START(efi32_boot_ds)
.word 0
SYM_DATA_END(efi32_boot_ds)
|
