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1// SPDX-License-Identifier: GPL-2.0-only
2/* -*- linux-c -*- ------------------------------------------------------- *
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * Copyright 2007 rPath, Inc. - All Rights Reserved
6 *
7 * ----------------------------------------------------------------------- */
8
9/*
10 * Prepare the machine for transition to protected mode.
11 */
12
13#include "boot.h"
14#include <asm/segment.h>
15
16/*
17 * Invoke the realmode switch hook if present; otherwise
18 * disable all interrupts.
19 */
20static void realmode_switch_hook(void)
21{
22 if (boot_params.hdr.realmode_swtch) {
23 asm volatile("lcallw *%0"
24 : : "m" (boot_params.hdr.realmode_swtch)
25 : "eax", "ebx", "ecx", "edx");
26 } else {
27 asm volatile("cli");
28 outb(0x80, 0x70); /* Disable NMI */
29 io_delay();
30 }
31}
32
33/*
34 * Disable all interrupts at the legacy PIC.
35 */
36static void mask_all_interrupts(void)
37{
38 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */
39 io_delay();
40 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */
41 io_delay();
42}
43
44/*
45 * Reset IGNNE# if asserted in the FPU.
46 */
47static void reset_coprocessor(void)
48{
49 outb(0, 0xf0);
50 io_delay();
51 outb(0, 0xf1);
52 io_delay();
53}
54
55/*
56 * Set up the GDT
57 */
58
59struct gdt_ptr {
60 u16 len;
61 u32 ptr;
62} __attribute__((packed));
63
64static void setup_gdt(void)
65{
66 /* There are machines which are known to not boot with the GDT
67 being 8-byte unaligned. Intel recommends 16 byte alignment. */
68 static const u64 boot_gdt[] __attribute__((aligned(16))) = {
69 /* CS: code, read/execute, 4 GB, base 0 */
70 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
71 /* DS: data, read/write, 4 GB, base 0 */
72 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
73 /* TSS: 32-bit tss, 104 bytes, base 4096 */
74 /* We only have a TSS here to keep Intel VT happy;
75 we don't actually use it for anything. */
76 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
77 };
78 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
79 of the gdt_ptr contents. Thus, make it static so it will
80 stay in memory, at least long enough that we switch to the
81 proper kernel GDT. */
82 static struct gdt_ptr gdt;
83
84 gdt.len = sizeof(boot_gdt)-1;
85 gdt.ptr = (u32)&boot_gdt + (ds() << 4);
86
87 asm volatile("lgdtl %0" : : "m" (gdt));
88}
89
90/*
91 * Set up the IDT
92 */
93static void setup_idt(void)
94{
95 static const struct gdt_ptr null_idt = {0, 0};
96 asm volatile("lidtl %0" : : "m" (null_idt));
97}
98
99/*
100 * Actual invocation sequence
101 */
102void go_to_protected_mode(void)
103{
104 /* Hook before leaving real mode, also disables interrupts */
105 realmode_switch_hook();
106
107 /* Enable the A20 gate */
108 if (enable_a20()) {
109 puts("A20 gate not responding, unable to boot...\n");
110 die();
111 }
112
113 /* Reset coprocessor (IGNNE#) */
114 reset_coprocessor();
115
116 /* Mask all interrupts in the PIC */
117 mask_all_interrupts();
118
119 /* Actual transition to protected mode... */
120 setup_idt();
121 setup_gdt();
122 protected_mode_jump(boot_params.hdr.code32_start,
123 (u32)&boot_params + (ds() << 4));
124}
1// SPDX-License-Identifier: GPL-2.0-only
2/* -*- linux-c -*- ------------------------------------------------------- *
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * Copyright 2007 rPath, Inc. - All Rights Reserved
6 *
7 * ----------------------------------------------------------------------- */
8
9/*
10 * Prepare the machine for transition to protected mode.
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; otherwise
19 * disable all interrupts.
20 */
21static void realmode_switch_hook(void)
22{
23 if (boot_params.hdr.realmode_swtch) {
24 asm volatile("lcallw *%0"
25 : : "m" (boot_params.hdr.realmode_swtch)
26 : "eax", "ebx", "ecx", "edx");
27 } else {
28 asm volatile("cli");
29 outb(0x80, 0x70); /* Disable NMI */
30 io_delay();
31 }
32}
33
34/*
35 * Disable all interrupts at the legacy PIC.
36 */
37static void mask_all_interrupts(void)
38{
39 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */
40 io_delay();
41 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */
42 io_delay();
43}
44
45/*
46 * Reset IGNNE# if asserted in the FPU.
47 */
48static 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
60struct gdt_ptr {
61 u16 len;
62 u32 ptr;
63} __attribute__((packed));
64
65static void setup_gdt(void)
66{
67 /* There are machines which are known to not boot with the GDT
68 being 8-byte unaligned. Intel recommends 16 byte alignment. */
69 static const u64 boot_gdt[] __attribute__((aligned(16))) = {
70 /* CS: code, read/execute, 4 GB, base 0 */
71 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(DESC_CODE32, 0, 0xfffff),
72 /* DS: data, read/write, 4 GB, base 0 */
73 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(DESC_DATA32, 0, 0xfffff),
74 /* TSS: 32-bit tss, 104 bytes, base 4096 */
75 /* We only have a TSS here to keep Intel VT happy;
76 we don't actually use it for anything. */
77 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(DESC_TSS32, 4096, 103),
78 };
79 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
80 of the gdt_ptr contents. Thus, make it static so it will
81 stay in memory, at least long enough that we switch to the
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 */
94static void setup_idt(void)
95{
96 static const struct gdt_ptr null_idt = {0, 0};
97 asm volatile("lidtl %0" : : "m" (null_idt));
98}
99
100/*
101 * Actual invocation sequence
102 */
103void go_to_protected_mode(void)
104{
105 /* Hook before leaving real mode, also disables interrupts */
106 realmode_switch_hook();
107
108 /* Enable the A20 gate */
109 if (enable_a20()) {
110 puts("A20 gate not responding, unable to boot...\n");
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.code32_start,
124 (u32)&boot_params + (ds() << 4));
125}