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