127 lines
3 KiB
C
127 lines
3 KiB
C
/* -*- linux-c -*- ------------------------------------------------------- *
|
|
*
|
|
* Copyright (C) 1991, 1992 Linus Torvalds
|
|
* Copyright 2007 rPath, Inc. - All Rights Reserved
|
|
*
|
|
* This file is part of the Linux kernel, and is made available under
|
|
* the terms of the GNU General Public License version 2.
|
|
*
|
|
* ----------------------------------------------------------------------- */
|
|
|
|
/*
|
|
* Prepare the machine for transition to protected mode.
|
|
*/
|
|
|
|
#include "boot.h"
|
|
#include <asm/segment.h>
|
|
|
|
/*
|
|
* Invoke the realmode switch hook if present; otherwise
|
|
* disable all interrupts.
|
|
*/
|
|
static void realmode_switch_hook(void)
|
|
{
|
|
if (boot_params.hdr.realmode_swtch) {
|
|
asm volatile("lcallw *%0"
|
|
: : "m" (boot_params.hdr.realmode_swtch)
|
|
: "eax", "ebx", "ecx", "edx");
|
|
} else {
|
|
asm volatile("cli");
|
|
outb(0x80, 0x70); /* Disable NMI */
|
|
io_delay();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Disable all interrupts at the legacy PIC.
|
|
*/
|
|
static void mask_all_interrupts(void)
|
|
{
|
|
outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */
|
|
io_delay();
|
|
outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */
|
|
io_delay();
|
|
}
|
|
|
|
/*
|
|
* Reset IGNNE# if asserted in the FPU.
|
|
*/
|
|
static void reset_coprocessor(void)
|
|
{
|
|
outb(0, 0xf0);
|
|
io_delay();
|
|
outb(0, 0xf1);
|
|
io_delay();
|
|
}
|
|
|
|
/*
|
|
* Set up the GDT
|
|
*/
|
|
|
|
struct gdt_ptr {
|
|
u16 len;
|
|
u32 ptr;
|
|
} __attribute__((packed));
|
|
|
|
static void setup_gdt(void)
|
|
{
|
|
/* There are machines which are known to not boot with the GDT
|
|
being 8-byte unaligned. Intel recommends 16 byte alignment. */
|
|
static const u64 boot_gdt[] __attribute__((aligned(16))) = {
|
|
/* CS: code, read/execute, 4 GB, base 0 */
|
|
[GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
|
|
/* DS: data, read/write, 4 GB, base 0 */
|
|
[GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
|
|
/* TSS: 32-bit tss, 104 bytes, base 4096 */
|
|
/* We only have a TSS here to keep Intel VT happy;
|
|
we don't actually use it for anything. */
|
|
[GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
|
|
};
|
|
/* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
|
|
of the gdt_ptr contents. Thus, make it static so it will
|
|
stay in memory, at least long enough that we switch to the
|
|
proper kernel GDT. */
|
|
static struct gdt_ptr gdt;
|
|
|
|
gdt.len = sizeof(boot_gdt)-1;
|
|
gdt.ptr = (u32)&boot_gdt + (ds() << 4);
|
|
|
|
asm volatile("lgdtl %0" : : "m" (gdt));
|
|
}
|
|
|
|
/*
|
|
* Set up the IDT
|
|
*/
|
|
static void setup_idt(void)
|
|
{
|
|
static const struct gdt_ptr null_idt = {0, 0};
|
|
asm volatile("lidtl %0" : : "m" (null_idt));
|
|
}
|
|
|
|
/*
|
|
* Actual invocation sequence
|
|
*/
|
|
void go_to_protected_mode(void)
|
|
{
|
|
/* Hook before leaving real mode, also disables interrupts */
|
|
realmode_switch_hook();
|
|
|
|
/* Enable the A20 gate */
|
|
if (enable_a20()) {
|
|
puts("A20 gate not responding, unable to boot...\n");
|
|
die();
|
|
}
|
|
|
|
/* Reset coprocessor (IGNNE#) */
|
|
reset_coprocessor();
|
|
|
|
/* Mask all interrupts in the PIC */
|
|
mask_all_interrupts();
|
|
|
|
/* Actual transition to protected mode... */
|
|
setup_idt();
|
|
setup_gdt();
|
|
protected_mode_jump(boot_params.hdr.code32_start,
|
|
(u32)&boot_params + (ds() << 4));
|
|
}
|