1 // SPDX-License-Identifier: GPL-2.0-only 1
2 /* -*- linux-c -*- ---------------------------
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * Copyright 2007 rPath, Inc. - All Rights R
6 *
7 * -------------------------------------------
8
9 /*
10 * Prepare the machine for transition to prote
11 */
12
13 #include "boot.h"
14 #include <asm/desc_defs.h>
15 #include <asm/segment.h>
16
17 /*
18 * Invoke the realmode switch hook if present;
19 * disable all interrupts.
20 */
21 static void realmode_switch_hook(void)
22 {
23 if (boot_params.hdr.realmode_swtch) {
24 asm volatile("lcallw *%0"
25 : : "m" (boot_par
26 : "eax", "ebx", "
27 } else {
28 asm volatile("cli");
29 outb(0x80, 0x70); /* Disable N
30 io_delay();
31 }
32 }
33
34 /*
35 * Disable all interrupts at the legacy PIC.
36 */
37 static void mask_all_interrupts(void)
38 {
39 outb(0xff, 0xa1); /* Mask all in
40 io_delay();
41 outb(0xfb, 0x21); /* Mask all bu
42 io_delay();
43 }
44
45 /*
46 * Reset IGNNE# if asserted in the FPU.
47 */
48 static void reset_coprocessor(void)
49 {
50 outb(0, 0xf0);
51 io_delay();
52 outb(0, 0xf1);
53 io_delay();
54 }
55
56 /*
57 * Set up the GDT
58 */
59
60 struct gdt_ptr {
61 u16 len;
62 u32 ptr;
63 } __attribute__((packed));
64
65 static void setup_gdt(void)
66 {
67 /* There are machines which are known
68 being 8-byte unaligned. Intel reco
69 static const u64 boot_gdt[] __attribut
70 /* CS: code, read/execute, 4 G
71 [GDT_ENTRY_BOOT_CS] = GDT_ENTR
72 /* DS: data, read/write, 4 GB,
73 [GDT_ENTRY_BOOT_DS] = GDT_ENTR
74 /* TSS: 32-bit tss, 104 bytes,
75 /* We only have a TSS here to
76 we don't actually use it fo
77 [GDT_ENTRY_BOOT_TSS] = GDT_ENT
78 };
79 /* Xen HVM incorrectly stores a pointe
80 of the gdt_ptr contents. Thus, mak
81 stay in memory, at least long enoug
82 proper kernel GDT. */
83 static struct gdt_ptr gdt;
84
85 gdt.len = sizeof(boot_gdt)-1;
86 gdt.ptr = (u32)&boot_gdt + (ds() << 4)
87
88 asm volatile("lgdtl %0" : : "m" (gdt))
89 }
90
91 /*
92 * Set up the IDT
93 */
94 static void setup_idt(void)
95 {
96 static const struct gdt_ptr null_idt =
97 asm volatile("lidtl %0" : : "m" (null_
98 }
99
100 /*
101 * Actual invocation sequence
102 */
103 void go_to_protected_mode(void)
104 {
105 /* Hook before leaving real mode, also
106 realmode_switch_hook();
107
108 /* Enable the A20 gate */
109 if (enable_a20()) {
110 puts("A20 gate not responding,
111 die();
112 }
113
114 /* Reset coprocessor (IGNNE#) */
115 reset_coprocessor();
116
117 /* Mask all interrupts in the PIC */
118 mask_all_interrupts();
119
120 /* Actual transition to protected mode
121 setup_idt();
122 setup_gdt();
123 protected_mode_jump(boot_params.hdr.co
124 (u32)&boot_params
125 }
126
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.