Re: [patch 1/2] KVM: x86: handle double and triple faults for every exception

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

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Avi Kivity wrote:
> On 11/15/2009 04:29 PM, Jan Kiszka wrote:
>> Avi Kivity wrote:
>>   
>>> On 11/15/2009 02:51 PM, Gleb Natapov wrote:
>>>     
>>>>       
>>>>> "replacing" exceptions is dangerous in the case of debug exceptions
>>>>> and machine checks, since restarting execution won't recover them.
>>>>>
>>>>>
>>>>>          
>>>> But not replacing them is not better. No point in re-injecting
>>>> exception that causes another exception.
>>>>
>>>>        
>>> Right, just pointing out there's still a small hole left.  Replacing is
>>> much better ignoring.
>>>      
>> Is the hardware doing some queuing in this case?
> 
> Gleb has verified by testing, and Intel has confirmed, that the hardware
> does not queue, and will in fact lose traps and NMIs in such a case.  So
> the small hole is actually present in the processor and we're better off
> not queueing!  I've forgotten about this but Gleb reminded me.
> 
>> Would it be overly
>> complicated to adopt the real behavior here?
>>    
> 
> Not only would it be difficult, it would also be incorrect.
> 

I'm all for correctness - so this correctly drop events. :)

Jan


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