Re: [Regression] kvm-userspace: VM freezes after booting FreeDOS

[Jan Kiszka <jan.kiszka@web.de>]

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Mohammed Gamal wrote:
> On Thu, Jul 10, 2008 at 11:02 PM, Anthony Liguori <anthony@codemonkey.ws> wrote:
>> Mohammed Gamal wrote:
>>> On Thu, Jul 10, 2008 at 7:31 PM, Anthony Liguori <anthony@codemonkey.ws>
>>> wrote:
>>>
>>>> Mohammed Gamal wrote:
>>>>
>>>>> After updating my kvm-userspace tree to the latest git tree. I am no
>>>>> more able to run FreeDOS. The VM freezes after choosing any of the
>>>>> boot options. I am running both latest kvm.git and kvm-userspace.git
>>>>>
>>>>>
>>>> Can you bisect to the commit that broke it?
>>>>
>>>> Regards,
>>>>
>>>> Anthony Liguori
>>>>
>>> I did, it seems that commit 04c3265c95c12e7c6e73cfd07357c05db6a1bda8
>>> caused it. Everything works fine after I reverted it.
>>>
>> Thats:
>>
>> commit 04c3265c95c12e7c6e73cfd07357c05db6a1bda8
>> Author: Jan Kiszka <jan.kiszka@web.de>
>> Date:   Fri May 16 09:21:47 2008 +0200
>>
>>   kvm: qemu: consolidate kvm_eat_signal
>>     With the io thread signals are rare.  Remove looping over
>>   kvm_eat_signal and fold everything into kvm_main_loop_wait.
>>     Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
>>   Signed-off-by: Avi Kivity <avi@qumranet.com>
>>
>>
>> Hrm, that's disturbing.  Unfortunately, the patch is a bit more than just
>> code motion.  It does change the number of times the lock is released and
>> makes some minor changes to the code.  Nothing obvious that would cause the
>> breakage without digging into it.
>>
>> How did you create your freedos image?  I'd like to try and figure out what
>> the problem is here since it may be causing other issues.
>>
> 
> The image is a 500M image created using qemu-img (not using qcow).
> FreeDOS was installed using the base CD image which you can get from
> here: http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.0/fdbasecd.iso
> 
> After booting FreeDOS, there are a number of boot options with
> different memory extenders, after selecting any option the system
> freezes and I get [Stopped] in thr QEMU title bar.

"Stopped" - interesting. Seems like something causes QEMU to stop the
guest as if some breakpoint was injected.

I just downloaded that image and gave it a try against vanilla kvm-70
and my own tree which is augment with guest debugging related patches.
The former shows your observed behavior (Boot from CD, provide an empty
HD image -> press '1' + ENTER -> press '1' -> "Stopped"). The latter kvm
tree made QEMU leave with a #GP in the guest. That may point to a debug
register related issue, and that patch you identified just happen to
make it visible. However, will try to investigate.

Jan


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