Re: High vm-exit latencies during kvm boot-up/shutdown

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Jan Kiszka wrote:
> Avi Kivity wrote:
>   
>> Jan Kiszka wrote:
>>     
>>> Got it! It's wbinvd from smm_init in rombios32.c! Anyone any comments on
>>> this?
>>>   
>>>       
>> Ha!  A real life 300usec instruction!
>>
>> Unfortunately, it cannot be trapped on Intel (it can be trapped on 
>> AMD).  Looks like a minor hole in VT, as a guest can generate very high 
>> latencies this way.
>>     
>
> I unfortunately do not have an AMD box at hand to test (I obviously
> order the wrong processor then...), but does this mean it is trapped by
> kvm-amd already? Or would there be more work required on that side?
>
>   

There's a two-liner required to make it work.  I'll add it soon.

>> For our bios, we can remove it, but there's no way to ensure an 
>> untrusted guest doesn't use it.
>>     
>
> Yep. Any ideas if and at which stages (bootup, normal operation) Windows
> is issues wbinvd noise?
>   

No idea.  I'll check it with an AMD machine.

I'd be surprised it it did that during normal operation.  It's also 
conceivable that it doesn't issue it at all.

-- 
error compiling committee.c: too many arguments to function


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