1 /* -*- linux-c -*- ------------------------------------------------------- *
2 *
3 * Copyright (C) 1991, 1992 Linus Torvalds
4 * Copyright 2007 rPath, Inc. - All Rights Reserved
5 *
6 * This file is part of the Linux kernel, and is made available under
7 * the terms of the GNU General Public License version 2.
8 *
9 * ----------------------------------------------------------------------- */
10
11 /*
12 * Prepare the machine for transition to protected mode.
13 */
14
15 #include "boot.h"
16 #include <asm/segment.h>
17
18 /*
19 * Invoke the realmode switch hook if present; otherwise
20 * disable all interrupts.
21 */
realmode_switch_hook(void)22 static void realmode_switch_hook(void)
23 {
24 if (boot_params.hdr.realmode_swtch) {
25 asm volatile("lcallw *%0"
26 : : "m" (boot_params.hdr.realmode_swtch)
27 : "eax", "ebx", "ecx", "edx");
28 } else {
29 asm volatile("cli");
30 outb(0x80, 0x70); /* Disable NMI */
31 io_delay();
32 }
33 }
34
35 /*
36 * Disable all interrupts at the legacy PIC.
37 */
mask_all_interrupts(void)38 static void mask_all_interrupts(void)
39 {
40 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */
41 io_delay();
42 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */
43 io_delay();
44 }
45
46 /*
47 * Reset IGNNE# if asserted in the FPU.
48 */
reset_coprocessor(void)49 static void reset_coprocessor(void)
50 {
51 outb(0, 0xf0);
52 io_delay();
53 outb(0, 0xf1);
54 io_delay();
55 }
56
57 /*
58 * Set up the GDT
59 */
60
61 struct gdt_ptr {
62 u16 len;
63 u32 ptr;
64 } __attribute__((packed));
65
setup_gdt(void)66 static void setup_gdt(void)
67 {
68 /* There are machines which are known to not boot with the GDT
69 being 8-byte unaligned. Intel recommends 16 byte alignment. */
70 static const u64 boot_gdt[] __attribute__((aligned(16))) = {
71 /* CS: code, read/execute, 4 GB, base 0 */
72 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
73 /* DS: data, read/write, 4 GB, base 0 */
74 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
75 /* TSS: 32-bit tss, 104 bytes, base 4096 */
76 /* We only have a TSS here to keep Intel VT happy;
77 we don't actually use it for anything. */
78 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
79 };
80 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
81 of the gdt_ptr contents. Thus, make it static so it will
82 stay in memory, at least long enough that we switch to the
83 proper kernel GDT. */
84 static struct gdt_ptr gdt;
85
86 gdt.len = sizeof(boot_gdt)-1;
87 gdt.ptr = (u32)&boot_gdt + (ds() << 4);
88
89 asm volatile("lgdtl %0" : : "m" (gdt));
90 }
91
92 /*
93 * Set up the IDT
94 */
setup_idt(void)95 static void setup_idt(void)
96 {
97 static const struct gdt_ptr null_idt = {0, 0};
98 asm volatile("lidtl %0" : : "m" (null_idt));
99 }
100
101 /*
102 * Actual invocation sequence
103 */
go_to_protected_mode(void)104 void go_to_protected_mode(void)
105 {
106 /* Hook before leaving real mode, also disables interrupts */
107 realmode_switch_hook();
108
109 /* Enable the A20 gate */
110 if (enable_a20()) {
111 puts("A20 gate not responding, unable to boot...\n");
112 die();
113 }
114
115 /* Reset coprocessor (IGNNE#) */
116 reset_coprocessor();
117
118 /* Mask all interrupts in the PIC */
119 mask_all_interrupts();
120
121 /* Actual transition to protected mode... */
122 setup_idt();
123 setup_gdt();
124 protected_mode_jump(boot_params.hdr.code32_start,
125 (u32)&boot_params + (ds() << 4));
126 }
127