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Date: Thu, 25 Sep 2008 10:04:17 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
       "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: v2.6.27-rc7: x86: #GP on panic?
Message-ID: <20080925080417.GB27048@elte.hu>
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* Vegard Nossum <vegard.nossum@gmail.com> wrote:

> Hi,
> 
> With 2.6.27-rc7 on qemu-x86_64, it seems that panic will trigger a 
> General Protection Fault. I haven't seen it before.

> [    4.523641] Code: eb fd 55 48 89 e5 53 51 83 3d 25 e8 78 00 00 75
> 1a 31 d2 31 f6 48 c7 c7 e1 9c 01 81 e8 f7 a4 03 00 9c 5b fa e8 94 09
> 00 00 53 9d <5a> 5b c9 c3 55 31 c0 48 89 e5 89 04 25 b0 c0 5f ff 65 83
> 04 25

hm, 0x5a is a simple pop %rdx. A #GP there means the stack segment is 
bust?

hm:

> ffffffff8101a6b9 <disable_local_APIC>
> ffffffff81019d25:       53                      push   %rbx
> ffffffff81019d26:       9d                      popfq
> ffffffff81019d27:       5a                      pop    %rdx

so it's preceded by a popfq and on the next instruction we #GP.

but the stack and flags state looks good:

  [    4.523641] RSP: 0018:ffff880007867d70  EFLAGS: 00000286

weird.

	Ingo