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97873a3d | 1 | // SPDX-License-Identifier: GPL-2.0-only |
7052fdd8 PA |
2 | /* -*- linux-c -*- ------------------------------------------------------- * |
3 | * | |
4 | * Copyright (C) 1991, 1992 Linus Torvalds | |
5 | * Copyright 2007 rPath, Inc. - All Rights Reserved | |
6 | * | |
7052fdd8 PA |
7 | * ----------------------------------------------------------------------- */ |
8 | ||
9 | /* | |
7052fdd8 PA |
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 | */ | |
20 | static 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 | ||
7052fdd8 PA |
33 | /* |
34 | * Disable all interrupts at the legacy PIC. | |
35 | */ | |
36 | static void mask_all_interrupts(void) | |
37 | { | |
8218d029 | 38 | outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ |
7052fdd8 PA |
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 | */ | |
47 | static 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 | */ | |
7052fdd8 PA |
58 | |
59 | struct gdt_ptr { | |
60 | u16 len; | |
61 | u32 ptr; | |
62 | } __attribute__((packed)); | |
63 | ||
64 | static 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), | |
88089519 PA |
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), | |
7052fdd8 | 77 | }; |
ce29a1f8 CE |
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; | |
7052fdd8 PA |
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 | */ | |
93 | static 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 | */ | |
102 | void go_to_protected_mode(void) | |
103 | { | |
104 | /* Hook before leaving real mode, also disables interrupts */ | |
105 | realmode_switch_hook(); | |
106 | ||
7052fdd8 PA |
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 | } |