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/desc_defs.h>
  15 #include <asm/segment.h>
  16
  17 /*
  18  * Invoke the realmode switch hook if present; otherwise
  19  * disable all interrupts.
  20  */
  21 static void realmode_switch_hook(void)
  22 {
  23         if (boot_params.hdr.realmode_swtch) {
  24                 asm volatile("lcallw *%0"
  25                              : : "m" (boot_params.hdr.realmode_swtch)
  26                              : "eax", "ebx", "ecx", "edx");
  27         } else {
  28                 asm volatile("cli");
  29                 outb(0x80, 0x70); /* Disable NMI */
  30                 io_delay();
  31         }
  32 }
  33
  34 /*
  35  * Disable all interrupts at the legacy PIC.
  36  */
  37 static void mask_all_interrupts(void)
  38 {
  39         outb(0xff, 0xa1);       /* Mask all interrupts on the secondary PIC */
  40         io_delay();
  41         outb(0xfb, 0x21);       /* Mask all but cascade on the primary PIC */
  42         io_delay();
  43 }
  44
  45 /*
  46  * Reset IGNNE# if asserted in the FPU.
  47  */
  48 static void reset_coprocessor(void)
  49 {
  50         outb(0, 0xf0);
  51         io_delay();
  52         outb(0, 0xf1);
  53         io_delay();
  54 }
  55
  56 /*
  57  * Set up the GDT
  58  */
  59
  60 struct gdt_ptr {
  61         u16 len;
  62         u32 ptr;
  63 } __attribute__((packed));
  64
  65 static void setup_gdt(void)
  66 {
  67         /* There are machines which are known to not boot with the GDT
  68            being 8-byte unaligned.  Intel recommends 16 byte alignment. */
  69         static const u64 boot_gdt[] __attribute__((aligned(16))) = {
  70                 /* CS: code, read/execute, 4 GB, base 0 */
  71                 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(DESC_CODE32, 0, 0xfffff),
  72                 /* DS: data, read/write, 4 GB, base 0 */
  73                 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(DESC_DATA32, 0, 0xfffff),
  74                 /* TSS: 32-bit tss, 104 bytes, base 4096 */
  75                 /* We only have a TSS here to keep Intel VT happy;
  76                    we don't actually use it for anything. */
  77                 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(DESC_TSS32, 4096, 103),
  78         };
  79         /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
  80            of the gdt_ptr contents.  Thus, make it static so it will
  81            stay in memory, at least long enough that we switch to the
  82            proper kernel GDT. */
  83         static struct gdt_ptr gdt;
  84
  85         gdt.len = sizeof(boot_gdt)-1;
  86         gdt.ptr = (u32)&boot_gdt + (ds() << 4);
  87
  88         asm volatile("lgdtl %0" : : "m" (gdt));
  89 }
  90
  91 /*
  92  * Set up the IDT
  93  */
  94 static void setup_idt(void)
  95 {
  96         static const struct gdt_ptr null_idt = {0, 0};
  97         asm volatile("lidtl %0" : : "m" (null_idt));
  98 }
  99
 100 /*
 101  * Actual invocation sequence
 102  */
 103 void go_to_protected_mode(void)
 104 {
 105         /* Hook before leaving real mode, also disables interrupts */
 106         realmode_switch_hook();
 107
 108         /* Enable the A20 gate */
 109         if (enable_a20()) {
 110                 puts("A20 gate not responding, unable to boot...\n");
 111                 die();
 112         }
 113
 114         /* Reset coprocessor (IGNNE#) */
 115         reset_coprocessor();
 116
 117         /* Mask all interrupts in the PIC */
 118         mask_all_interrupts();
 119
 120         /* Actual transition to protected mode... */
 121         setup_idt();
 122         setup_gdt();
 123         protected_mode_jump(boot_params.hdr.code32_start,
 124                             (u32)&boot_params + (ds() << 4));
 125 }