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 | */ |
21 | static 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 | */ |
37 | static 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 | */ |
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 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 | */ |
94 | static 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 | */ |
103 | void 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(entrypoint: boot_params.hdr.code32_start, |
124 | bootparams: (u32)&boot_params + (ds() << 4)); |
125 | } |
126 | |