pm.c

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/* -*- 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));
}