xref: /kernel/linux/linux-6.6/arch/x86/boot/pm.c (revision 62306a36) 
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}
125