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// SPDX-License-Identifier: GPL-2.0-only
/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007 rPath, Inc. - All Rights Reserved
*
* ----------------------------------------------------------------------- */
/*
* 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));
}
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