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  * arch/i386/boot/pm.c
  13  *
  14  * Prepare the machine for transition to protected mode.
  15  */
  16
  17 #include "boot.h"
  18 #include <asm/segment.h>
  19
  20 /*
  21  * Invoke the realmode switch hook if present; otherwise
  22  * disable all interrupts.
  23  */
  24 static void realmode_switch_hook(void)
  25 {
  26         if (boot_params.hdr.realmode_swtch) {
  27                 asm volatile("lcallw *%0"
  28                              : : "m" (boot_params.hdr.realmode_swtch)
  29                              : "eax", "ebx", "ecx", "edx");
  30         } else {
  31                 asm volatile("cli");
  32                 outb(0x80, 0x70); /* Disable NMI */
  33                 io_delay();
  34         }
  35 }
  36
  37 /*
  38  * A zImage kernel is loaded at 0x10000 but wants to run at 0x1000.
  39  * A bzImage kernel is loaded and runs at 0x100000.
  40  */
  41 static void move_kernel_around(void)
  42 {
  43         /* Note: rely on the compile-time option here rather than
  44            the LOADED_HIGH flag.  The Qemu kernel loader unconditionally
  45            sets the loadflags to zero. */
  46 #ifndef __BIG_KERNEL__
  47         u16 dst_seg, src_seg;
  48         u32 syssize;
  49
  50         dst_seg =  0x1000 >> 4;
  51         src_seg = 0x10000 >> 4;
  52         syssize = boot_params.hdr.syssize; /* Size in 16-byte paragraphs */
  53
  54         while (syssize) {
  55                 int paras  = (syssize >= 0x1000) ? 0x1000 : syssize;
  56                 int dwords = paras << 2;
  57
  58                 asm volatile("pushw %%es ; "
  59                              "pushw %%ds ; "
  60                              "movw %1,%%es ; "
  61                              "movw %2,%%ds ; "
  62                              "xorw %%di,%%di ; "
  63                              "xorw %%si,%%si ; "
  64                              "rep;movsl ; "
  65                              "popw %%ds ; "
  66                              "popw %%es"
  67                              : "+c" (dwords)
  68                              : "r" (dst_seg), "r" (src_seg)
  69                              : "esi", "edi");
  70
  71                 syssize -= paras;
  72                 dst_seg += paras;
  73                 src_seg += paras;
  74         }
  75 #endif
  76 }
  77
  78 /*
  79  * Disable all interrupts at the legacy PIC.
  80  */
  81 static void mask_all_interrupts(void)
  82 {
  83         outb(0xff, 0xa1);       /* Mask all interrupts on the secondary PIC */
  84         io_delay();
  85         outb(0xfb, 0x21);       /* Mask all but cascade on the primary PIC */
  86         io_delay();
  87 }
  88
  89 /*
  90  * Reset IGNNE# if asserted in the FPU.
  91  */
  92 static void reset_coprocessor(void)
  93 {
  94         outb(0, 0xf0);
  95         io_delay();
  96         outb(0, 0xf1);
  97         io_delay();
  98 }
  99
 100 /*
 101  * Set up the GDT
 102  */
 103 #define GDT_ENTRY(flags,base,limit)             \
 104         (((u64)(base & 0xff000000) << 32) |     \
 105          ((u64)flags << 40) |                   \
 106          ((u64)(limit & 0x00ff0000) << 32) |    \
 107          ((u64)(base & 0x00ffffff) << 16) |     \
 108          ((u64)(limit & 0x0000ffff)))
 109
 110 struct gdt_ptr {
 111         u16 len;
 112         u32 ptr;
 113 } __attribute__((packed));
 114
 115 static void setup_gdt(void)
 116 {
 117         /* There are machines which are known to not boot with the GDT
 118            being 8-byte unaligned.  Intel recommends 16 byte alignment. */
 119         static const u64 boot_gdt[] __attribute__((aligned(16))) = {
 120                 /* CS: code, read/execute, 4 GB, base 0 */
 121                 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
 122                 /* DS: data, read/write, 4 GB, base 0 */
 123                 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
 124                 /* TSS: 32-bit tss, 104 bytes, base 4096 */
 125                 /* We only have a TSS here to keep Intel VT happy;
 126                    we don't actually use it for anything. */
 127                 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
 128         };
 129         /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
 130            of the gdt_ptr contents.  Thus, make it static so it will
 131            stay in memory, at least long enough that we switch to the
 132            proper kernel GDT. */
 133         static struct gdt_ptr gdt;
 134
 135         gdt.len = sizeof(boot_gdt)-1;
 136         gdt.ptr = (u32)&boot_gdt + (ds() << 4);
 137
 138         asm volatile("lgdtl %0" : : "m" (gdt));
 139 }
 140
 141 /*
 142  * Set up the IDT
 143  */
 144 static void setup_idt(void)
 145 {
 146         static const struct gdt_ptr null_idt = {0, 0};
 147         asm volatile("lidtl %0" : : "m" (null_idt));
 148 }
 149
 150 /*
 151  * Actual invocation sequence
 152  */
 153 void go_to_protected_mode(void)
 154 {
 155         /* Hook before leaving real mode, also disables interrupts */
 156         realmode_switch_hook();
 157
 158         /* Move the kernel/setup to their final resting places */
 159         move_kernel_around();
 160
 161         /* Enable the A20 gate */
 162         if (enable_a20()) {
 163                 puts("A20 gate not responding, unable to boot...\n");
 164                 die();
 165         }
 166
 167         /* Reset coprocessor (IGNNE#) */
 168         reset_coprocessor();
 169
 170         /* Mask all interrupts in the PIC */
 171         mask_all_interrupts();
 172
 173         /* Actual transition to protected mode... */
 174         setup_idt();
 175         setup_gdt();
 176         protected_mode_jump(boot_params.hdr.code32_start,
 177                             (u32)&boot_params + (ds() << 4));
 178 }