Re: [Xen-devel] [PATCH 0/2] MTRR/PAT virtualization

To:	"Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH 0/2] MTRR/PAT virtualization
From:	"Michael A Fetterman" <Michael.Fetterman@xxxxxxxxxxxx>
Date:	Tue, 9 Oct 2007 10:23:37 +0100
Cc:	"Su, Disheng" <disheng.su@xxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date:	Tue, 09 Oct 2007 02:24:17 -0700
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> > But, yes this is really a good point. So we need to do WBINVD when VP
> > migrates (of course for pass-through domain only), while the prefered
> > approach is to pin VCPU on pCPUs.
>
> Or WBINVD all CPUs when a VCPU executes WBINVD. Or explicitly track dirty
> caches for each vCPU.

I shutter to think of allowing a guest to cause a WBINVD.

In modern systems (8M+ of cache, etc), it can take 4+ milliseconds to execute.
I dare say it could, in a worst case scenerio, be even worse if you
did it on multiple
CPUs or hyperthreads at once.  And the cpu is non-interruptable the entire time.

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Re: [Xen-devel] [PATCH 0/2] MTRR/PAT virtualization