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/*

 * Switch back to real mode and call the BIOS reboot vector.

 * This is a trampoline copied around in process.c

 * Written 2003 by Andi Kleen, SuSE Labs.

 */

#include 

#define R(x) x-warm_reboot(%ebx)

#define R64(x) x-warm_reboot(%rbx)

        /* running in identity mapping and in the first 64k of memory

           and in compatibility mode. This must be position independent */

        /* Follows 14.7 "Leaving Long Mode" in the AMD x86-64 manual, volume 2

           and 8.9.2 "Switching Back to Real-Address Mode" in the Intel IA32

           manual, volume 2 */

        /* ebx: self pointer to warm_reboot */

        .globl warm_reboot

warm_reboot:

        addl  %ebx,  R64(real_mode_desc)        /* relocate tables */

        addl  %ebx,2+R64(warm_gdt_desc)

        movq  %cr0,%rax

        btr  $31,%rax

        movq %rax,%cr0          /* disable paging */

        jmp  1f                 /* flush prefetch queue */

        .code32

1:      movl $MSR_EFER,%ecx

        rdmsr

        andl $~((1<<_EFER_LME)|(1<<_EFER_SCE)|(1<<_EFER_NX)),%eax

        wrmsr                   /* disable long mode in EFER */

        xorl %eax,%eax

        movl %eax,%cr3          /* flush tlb */

        /* Running protected mode without paging now */

        wbinvd                  /* flush caches. Needed? */

        lidt R(warm_idt_desc)

        lgdt R(warm_gdt_desc)

        movl $0x10,%ecx         /* load segment registers with real mode settings */

        movl %ecx,%ds

        movl %ecx,%es

        movl %ecx,%fs

        movl %ecx,%gs

        movl %ecx,%ss

        lea  R(real_mode_desc),%eax

        ljmp *(%eax)

        .code16:

real_mode:

        xorl %eax,%eax

        movl %eax,%cr0

        /* some people claim $0xf000,0xfff0 is better. Use what 32bit linux uses. */

        /* code as bytes because gas has problems with it */

        .byte   0xea,0xf0,0xff,0x00,0xf0        /* ljmp  0xf000:0xfff0 */

real_mode_desc:

        .long  real_mode - warm_reboot

        .short 8

warm_gdt_desc:

        .short 8*3

        .long warm_gdt - warm_reboot

warm_gdt:

        .quad   0

        .quad   0x00009a000000ffff      /* 16-bit real-mode 64k code at 0x00000000 */

        .quad   0x000092000100ffff      /* 16-bit real-mode 64k data at 0x00000100 */

warm_idt_desc:

        .short 0x3ff

        .long  0

        .globl warm_reboot_end

warm_reboot_end: