1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * Copyright (C) 2014 Intel Corporation; author Matt Fleming 4 * 5 * Support for invoking 32-bit EFI runtime services from a 64-bit 6 * kernel. 7 * 8 * The below thunking functions are only used after ExitBootServices() 9 * has been called. This simplifies things considerably as compared with 10 * the early EFI thunking because we can leave all the kernel state 11 * intact (GDT, IDT, etc) and simply invoke the the 32-bit EFI runtime 12 * services from __KERNEL32_CS. This means we can continue to service 13 * interrupts across an EFI mixed mode call. 14 * 15 * We do however, need to handle the fact that we're running in a full 16 * 64-bit virtual address space. Things like the stack and instruction 17 * addresses need to be accessible by the 32-bit firmware, so we rely on 18 * using the identity mappings in the EFI page table to access the stack 19 * and kernel text (see efi_setup_page_tables()). 20 */ 21 22#include <linux/linkage.h> 23#include <asm/page_types.h> 24#include <asm/segment.h> 25 26 .text 27 .code64 28SYM_CODE_START(__efi64_thunk) 29 push %rbp 30 push %rbx 31 32 /* 33 * Switch to 1:1 mapped 32-bit stack pointer. 34 */ 35 movq %rsp, %rax 36 movq efi_scratch(%rip), %rsp 37 push %rax 38 39 /* 40 * Calculate the physical address of the kernel text. 41 */ 42 movq $__START_KERNEL_map, %rax 43 subq phys_base(%rip), %rax 44 45 leaq 1f(%rip), %rbp 46 leaq 2f(%rip), %rbx 47 subq %rax, %rbp 48 subq %rax, %rbx 49 50 subq $28, %rsp 51 movl %ebx, 0x0(%rsp) /* return address */ 52 movl %esi, 0x4(%rsp) 53 movl %edx, 0x8(%rsp) 54 movl %ecx, 0xc(%rsp) 55 movl %r8d, 0x10(%rsp) 56 movl %r9d, 0x14(%rsp) 57 58 /* Switch to 32-bit descriptor */ 59 pushq $__KERNEL32_CS 60 pushq %rdi /* EFI runtime service address */ 61 lretq 62 631: movq 24(%rsp), %rsp 64 pop %rbx 65 pop %rbp 66 retq 67 68 .code32 692: pushl $__KERNEL_CS 70 pushl %ebp 71 lret 72SYM_CODE_END(__efi64_thunk) 73