tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/*
2 * Copyright (C) 2014, 2015 Intel Corporation; author Matt Fleming
3 *
4 * Early support for invoking 32-bit EFI services from a 64-bit kernel.
5 *
6 * Because this thunking occurs before ExitBootServices() we have to
7 * restore the firmware's 32-bit GDT before we make EFI serivce calls,
8 * since the firmware's 32-bit IDT is still currently installed and it
9 * needs to be able to service interrupts.
10 *
11 * On the plus side, we don't have to worry about mangling 64-bit
12 * addresses into 32-bits because we're executing with an identify
13 * mapped pagetable and haven't transitioned to 64-bit virtual addresses
14 * yet.
15 */
16
17#include <linux/linkage.h>
18#include <asm/msr.h>
19#include <asm/page_types.h>
20#include <asm/processor-flags.h>
21#include <asm/segment.h>
22
23 .code64
24 .text
25ENTRY(efi64_thunk)
26 push %rbp
27 push %rbx
28
29 subq $8, %rsp
30 leaq efi_exit32(%rip), %rax
31 movl %eax, 4(%rsp)
32 leaq efi_gdt64(%rip), %rax
33 movl %eax, (%rsp)
34 movl %eax, 2(%rax) /* Fixup the gdt base address */
35
36 movl %ds, %eax
37 push %rax
38 movl %es, %eax
39 push %rax
40 movl %ss, %eax
41 push %rax
42
43 /*
44 * Convert x86-64 ABI params to i386 ABI
45 */
46 subq $32, %rsp
47 movl %esi, 0x0(%rsp)
48 movl %edx, 0x4(%rsp)
49 movl %ecx, 0x8(%rsp)
50 movq %r8, %rsi
51 movl %esi, 0xc(%rsp)
52 movq %r9, %rsi
53 movl %esi, 0x10(%rsp)
54
55 sgdt save_gdt(%rip)
56
57 leaq 1f(%rip), %rbx
58 movq %rbx, func_rt_ptr(%rip)
59
60 /*
61 * Switch to gdt with 32-bit segments. This is the firmware GDT
62 * that was installed when the kernel started executing. This
63 * pointer was saved at the EFI stub entry point in head_64.S.
64 */
65 leaq efi32_boot_gdt(%rip), %rax
66 lgdt (%rax)
67
68 pushq $__KERNEL_CS
69 leaq efi_enter32(%rip), %rax
70 pushq %rax
71 lretq
72
731: addq $32, %rsp
74
75 lgdt save_gdt(%rip)
76
77 pop %rbx
78 movl %ebx, %ss
79 pop %rbx
80 movl %ebx, %es
81 pop %rbx
82 movl %ebx, %ds
83
84 /*
85 * Convert 32-bit status code into 64-bit.
86 */
87 test %rax, %rax
88 jz 1f
89 movl %eax, %ecx
90 andl $0x0fffffff, %ecx
91 andl $0xf0000000, %eax
92 shl $32, %rax
93 or %rcx, %rax
941:
95 addq $8, %rsp
96 pop %rbx
97 pop %rbp
98 ret
99ENDPROC(efi64_thunk)
100
101ENTRY(efi_exit32)
102 movq func_rt_ptr(%rip), %rax
103 push %rax
104 mov %rdi, %rax
105 ret
106ENDPROC(efi_exit32)
107
108 .code32
109/*
110 * EFI service pointer must be in %edi.
111 *
112 * The stack should represent the 32-bit calling convention.
113 */
114ENTRY(efi_enter32)
115 movl $__KERNEL_DS, %eax
116 movl %eax, %ds
117 movl %eax, %es
118 movl %eax, %ss
119
120 /* Reload pgtables */
121 movl %cr3, %eax
122 movl %eax, %cr3
123
124 /* Disable paging */
125 movl %cr0, %eax
126 btrl $X86_CR0_PG_BIT, %eax
127 movl %eax, %cr0
128
129 /* Disable long mode via EFER */
130 movl $MSR_EFER, %ecx
131 rdmsr
132 btrl $_EFER_LME, %eax
133 wrmsr
134
135 call *%edi
136
137 /* We must preserve return value */
138 movl %eax, %edi
139
140 /*
141 * Some firmware will return with interrupts enabled. Be sure to
142 * disable them before we switch GDTs.
143 */
144 cli
145
146 movl 56(%esp), %eax
147 movl %eax, 2(%eax)
148 lgdtl (%eax)
149
150 movl %cr4, %eax
151 btsl $(X86_CR4_PAE_BIT), %eax
152 movl %eax, %cr4
153
154 movl %cr3, %eax
155 movl %eax, %cr3
156
157 movl $MSR_EFER, %ecx
158 rdmsr
159 btsl $_EFER_LME, %eax
160 wrmsr
161
162 xorl %eax, %eax
163 lldt %ax
164
165 movl 60(%esp), %eax
166 pushl $__KERNEL_CS
167 pushl %eax
168
169 /* Enable paging */
170 movl %cr0, %eax
171 btsl $X86_CR0_PG_BIT, %eax
172 movl %eax, %cr0
173 lret
174ENDPROC(efi_enter32)
175
176 .data
177 .balign 8
178 .global efi32_boot_gdt
179efi32_boot_gdt: .word 0
180 .quad 0
181
182save_gdt: .word 0
183 .quad 0
184func_rt_ptr: .quad 0
185
186 .global efi_gdt64
187efi_gdt64:
188 .word efi_gdt64_end - efi_gdt64
189 .long 0 /* Filled out by user */
190 .word 0
191 .quad 0x0000000000000000 /* NULL descriptor */
192 .quad 0x00af9a000000ffff /* __KERNEL_CS */
193 .quad 0x00cf92000000ffff /* __KERNEL_DS */
194 .quad 0x0080890000000000 /* TS descriptor */
195 .quad 0x0000000000000000 /* TS continued */
196efi_gdt64_end: