Re: qemu-kvm-1.1.0 crashing with kernel 3.5.0-rc6

[Chris Clayton <chris2553@googlemail.com>]

On 07/29/12 18:54, Gleb Natapov wrote:
> On Sun, Jul 29, 2012 at 06:50:09PM +0100, Chris Clayton wrote:
>> On 07/29/12 17:34, Avi Kivity wrote:
>>> On 07/29/2012 06:47 PM, Avi Kivity wrote:
>>>>> What might have happened is that the movdqu instruction faulted (as it's
>>>>> an fpu instruction), and on the way back from the fault, ds and es
>>>>> didn't get restored correctly.
>>>>>
>>>>> You can test this by writing a trivial version of g_str_equal()
>>>>> somewhere in the qemu source code and rebuilding it.
>>>>>
>>>>>
>>>>
>>> >from entry_32.S:
>>>>
>>>> .macro RESTORE_REGS pop=0
>>>> 	RESTORE_INT_REGS
>>>> 1:	popl_cfi %ds
>>>> 	/*CFI_RESTORE ds;*/
>>>> 2:	popl_cfi %es
>>>> 	/*CFI_RESTORE es;*/
>>>> 3:	popl_cfi %fs
>>>> 	/*CFI_RESTORE fs;*/
>>>> 	POP_GS \pop
>>>> .pushsection .fixup, "ax"
>>>> 4:	movl $0, (%esp)
>>>> 	jmp 1b
>>>> 5:	movl $0, (%esp)
>>>> 	jmp 2b
>>>> 6:	movl $0, (%esp)
>>>> 	jmp 3b
>>>> .popsection
>>>>
>>>> this piece of code tries to restore %ds, and if it fails, zeros it,
>>>> which is consistent with the core dump.
>>>>
>>>> This could happen if kvm is failing to restore GDT correctly.
>>>>
>>>
>>> Possible culprit: b2da15ac26a0c00.
>>>
>>>
>> That commit isn't in qermu-kvm-1.1.1.
>>
> It is in kernel.
>

Sorry, so it is.

With kernel 3.5.0 with b2da15ac26a0c00 reverted, I have just had 15 
clean invocations of vanilla qemu-kvm-1.1.1. So that commit would seem 
to be the problem.

>> I'm testing a build with g_str_equal implemented in kvm.c and so far
>> I haven't had a crash in 6 invocations. That hasn't been possible
>> with vanilla qemu-kvm-1.1.{0,1}, but I'll do a few more, just to be
>> sure.
>>

Similarly, with my "local" implementation of g_str_equal, I've had 15 
clean invocations on vanilla kernel 3.5.0.

I'm more than happy to test patches to fix this regression, but it will 
be tomorrow before I will be able to do so.

>> Thanks for your help, Avi.
>
> --
> 			Gleb.
>