arch/x86/boot/pm.c

   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  */
  20 static 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  */
  36 static 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  */
  47 static 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
  59 struct gdt_ptr {
  60         u16 len;
  61         u32 ptr;
  62 } __attribute__((packed));
  63
  64 static 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  */
  93 static 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  */
 102 void 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 }