LXR linux/arch/x86/boot/pm.c

   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 */
  22static 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 */
  38static 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 */
  49static 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
  61struct gdt_ptr {
  62        u16 len;
  63        u32 ptr;
  64} __attribute__((packed));
  65
  66static 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 */
  95static 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 */
 104void 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