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

Avi Kivity
2007-10-25T18:02:42Z

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