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  */
  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  */
  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  */
  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
  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  */
  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  */
 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 }