Re: [PATCH] KVM: VMX: Enable memory mappedTPR shadow(FlexPriority)

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

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Dong, Eddie wrote:
>>
>>> From: Sheng Yang <sheng.yang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>>> Date: Mon, 29 Oct 2007 09:40:42 +0800
>>> Subject: [PATCH] KVM: VMX: Enable memory mapped TPR 
>>>       
>> shadow(FlexPriority)
>>     
>>> This patch based on CR8/TPR patch, and enable the TPR
>>> shadow(FlexPriority)
>>> for 32bit Windows. Since TPR is accessed very frequently by 32bit
>>> Windows,
>>> especially SMP guest, with FlexPriority enabled, we saw significant
>>> performance gain.
>>>       
>> patch look much better, and everything seems to be fine as i 
>> look at it.
>> lets wait avi to review it
>>
>>     
> Ack too :-)
>
> Basically this patch will have same functionality/result with what Avi
> did for optimizing Windows. Dynamic patch works on all HWs, but
> may crash the guest if guest kernel has integrity check or patch
> guard. This one avoid this issue, but require new HWs :-)
>
> I assume all comming processor will have this feature, some existing
> processor also has this feature, so now we can have whole bunch of
> solution: new HW will use HW features + any modern OSes;
> old HWs will use dynamic patching with assumption no patch guard in guest
> which is true so far.
>   

Yes. FlexPriority will be both faster and safer for those who have it
than my hack.

It may turn out that patching can improve performance even with
FlexPriority: we can patch the APIC EOI write to look if any interrupts
are pending, and only exit if the EOI will result in a new interrupt
being injected. But it is very possible that this will not be necessary
if we can achieve good interrupt mitigation with virtio.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.



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