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x86: fix regression: boot failure on AMD Elan TS-5500

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Jeremy Fitzhardinge wrote:
>
> Maybe it really does require the far jump immediately after setting PE
> in cr0...
>
> Hm, I don't remember this paragraph being in vol 3a, section 8.9.1
> before.  Is it a recent addition?
>
>    Random failures can occur if other instructions exist between steps
>    3 and 4 above.  Failures will be readily seen in some situations,
>    such as when instructions that reference memory are inserted between
>    steps 3 and 4 while in system management mode.
>

I don't remember that, either.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
H. Peter Anvin 2008-06-30 15:42:47 -07:00 committed by Ingo Molnar
parent 908ec7afac
commit 2ee2394b68
1 changed files with 2 additions and 2 deletions
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4
arch/x86/boot/pmjump.S
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@ -33,6 +33,8 @@ protected_mode_jump:
movw %cs, %bx
shll $4, %ebx
addl %ebx, 2f
jmp 1f # Short jump to serialize on 386/486
1:
movw $__BOOT_DS, %cx
movw $__BOOT_TSS, %di
@ -40,8 +42,6 @@ protected_mode_jump:
movl %cr0, %edx
orb $X86_CR0_PE, %dl # Protected mode
movl %edx, %cr0
jmp 1f # Short jump to serialize on 386/486
1:
# Transition to 32-bit mode
.byte 0x66, 0xea # ljmpl opcode