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  * A zImage kernel is loaded at 0x10000 but wants to run at 0x1000.
  37  * A bzImage kernel is loaded and runs at 0x100000.
  38  */
  39 static void move_kernel_around(void)
  40 {
  41         /* Note: rely on the compile-time option here rather than
  42            the LOADED_HIGH flag.  The Qemu kernel loader unconditionally
  43            sets the loadflags to zero. */
  44 #ifndef __BIG_KERNEL__
  45         u16 dst_seg, src_seg;
  46         u32 syssize;
  47
  48         dst_seg =  0x1000 >> 4;
  49         src_seg = 0x10000 >> 4;
  50         syssize = boot_params.hdr.syssize; /* Size in 16-byte paragraphs */
  51
  52         while (syssize) {
  53                 int paras  = (syssize >= 0x1000) ? 0x1000 : syssize;
  54                 int dwords = paras << 2;
  55
  56                 asm volatile("pushw %%es ; "
  57                              "pushw %%ds ; "
  58                              "movw %1,%%es ; "
  59                              "movw %2,%%ds ; "
  60                              "xorw %%di,%%di ; "
  61                              "xorw %%si,%%si ; "
  62                              "rep;movsl ; "
  63                              "popw %%ds ; "
  64                              "popw %%es"
  65                              : "+c" (dwords)
  66                              : "r" (dst_seg), "r" (src_seg)
  67                              : "esi", "edi");
  68
  69                 syssize -= paras;
  70                 dst_seg += paras;
  71                 src_seg += paras;
  72         }
  73 #endif
  74 }
  75
  76 /*
  77  * Disable all interrupts at the legacy PIC.
  78  */
  79 static void mask_all_interrupts(void)
  80 {
  81         outb(0xff, 0xa1);       /* Mask all interrupts on the secondary PIC */
  82         io_delay();
  83         outb(0xfb, 0x21);       /* Mask all but cascade on the primary PIC */
  84         io_delay();
  85 }
  86
  87 /*
  88  * Reset IGNNE# if asserted in the FPU.
  89  */
  90 static void reset_coprocessor(void)
  91 {
  92         outb(0, 0xf0);
  93         io_delay();
  94         outb(0, 0xf1);
  95         io_delay();
  96 }
  97
  98 /*
  99  * Set up the GDT
 100  */
 101 #define GDT_ENTRY(flags, base, limit)           \
 102         (((u64)(base & 0xff000000) << 32) |     \
 103          ((u64)flags << 40) |                   \
 104          ((u64)(limit & 0x00ff0000) << 32) |    \
 105          ((u64)(base & 0x00ffffff) << 16) |     \
 106          ((u64)(limit & 0x0000ffff)))
 107
 108 struct gdt_ptr {
 109         u16 len;
 110         u32 ptr;
 111 } __attribute__((packed));
 112
 113 static void setup_gdt(void)
 114 {
 115         /* There are machines which are known to not boot with the GDT
 116            being 8-byte unaligned.  Intel recommends 16 byte alignment. */
 117         static const u64 boot_gdt[] __attribute__((aligned(16))) = {
 118                 /* CS: code, read/execute, 4 GB, base 0 */
 119                 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
 120                 /* DS: data, read/write, 4 GB, base 0 */
 121                 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
 122                 /* TSS: 32-bit tss, 104 bytes, base 4096 */
 123                 /* We only have a TSS here to keep Intel VT happy;
 124                    we don't actually use it for anything. */
 125                 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
 126         };
 127         /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
 128            of the gdt_ptr contents.  Thus, make it static so it will
 129            stay in memory, at least long enough that we switch to the
 130            proper kernel GDT. */
 131         static struct gdt_ptr gdt;
 132
 133         gdt.len = sizeof(boot_gdt)-1;
 134         gdt.ptr = (u32)&boot_gdt + (ds() << 4);
 135
 136         asm volatile("lgdtl %0" : : "m" (gdt));
 137 }
 138
 139 /*
 140  * Set up the IDT
 141  */
 142 static void setup_idt(void)
 143 {
 144         static const struct gdt_ptr null_idt = {0, 0};
 145         asm volatile("lidtl %0" : : "m" (null_idt));
 146 }
 147
 148 /*
 149  * Actual invocation sequence
 150  */
 151 void go_to_protected_mode(void)
 152 {
 153         /* Hook before leaving real mode, also disables interrupts */
 154         realmode_switch_hook();
 155
 156         /* Move the kernel/setup to their final resting places */
 157         move_kernel_around();
 158
 159         /* Enable the A20 gate */
 160         if (enable_a20()) {
 161                 puts("A20 gate not responding, unable to boot...\n");
 162                 die();
 163         }
 164
 165         /* Reset coprocessor (IGNNE#) */
 166         reset_coprocessor();
 167
 168         /* Mask all interrupts in the PIC */
 169         mask_all_interrupts();
 170
 171         /* Actual transition to protected mode... */
 172         setup_idt();
 173         setup_gdt();
 174         protected_mode_jump(boot_params.hdr.code32_start,
 175                             (u32)&boot_params + (ds() << 4));
 176 }