[Qemu-devel] Re: [PATCH] x86: Reboot CPU on triple fault - Version 4

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

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Anthony Liguori wrote:
> Jan Kiszka wrote:
>> Anthony Liguori wrote:
>>  
>>> Jan Kiszka wrote:
>>>     You can always check within the guest to see if it's rebooted (via
>>> uptime for instance).
>>>     
>>
>> But you won't find the CPU state on triple fault there.
>>   
> 
> Nor will you with your patch.

Provided "-d cpu_reset" with Kevin's last patch, they are. I tried it,
it worked, that's why I acked it.

> 
>>> It's extremely unlikely you'll ever see an OS triple fault in the wild
>>> unless you're doing kernel development.  Triple faulting requires a bad
>>> IDT or a really bad page table both of which are not something an OS is
>>> likely to do by accident.  If your OS is triple faulting, I highly doubt
>>> it's just going to reboot and everything's going to be okay.
>>>     
>>
>> There are various OSes out there in the wild. Not all of them conform to
>> common assumptions about how OSes typically look like. And once you
>> start moving things under a different roof (like QEMU), you are better
>> off logging such /potentially/ critical events (specifically if that
>> roof is a bit smaller due to missing segment limit and type checks).
>> That's at least our situation ATM.
>>   
> 
> It's not a question of whether it's logged, it's a question of whether
> it gets logged *specially*.  That's the crux of the discussion here.  My
> argument is that triple faults are not sufficiently special that they
> warrant *special* logging.

Depends on the POV. But I really think we loose nothing with the latest
patch, rather gain a useful feature for certain (granted) corner cases.

Jan


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