Re: [PATCH] KVM: SVM: Add xsetbv intercept

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On 12/06/2010 07:48 PM, Roedel, Joerg wrote:
On Mon, Dec 06, 2010 at 11:10:46AM -0500, Avi Kivity wrote:
>  On 12/03/2010 06:42 PM, Joerg Roedel wrote:
>  >  This patch implements the xsetbv intercept to the AMD part
>  >  of KVM. This makes AVX usable in a save way for the guest on
>  >  AVX capable AMD hardware.
>  >  The patch is tested by using AVX in the guest and host in
>  >  parallel and checking for data corruption. I also used the
>  >  KVM xsave unit-tests and they all pass.
>  >
>
>  That is really strange.  You didn't need to do anything to get cpuid.avx
>  recognized.  So running an older kvm on newer hardware will happily
>  expose avx even though it's not supported.
>
>  We screwed up - we should have made cpuid.avx dependent on vendor support.

Hmm, right. The set_supported_cpuid arch-callback should basically
disable xsave on AMD for all KVM versions which do not handle the xsetbv
intercept.


Please post a patch to do that, and update this patch to undo the change. We'll backport the first patch to -stable so that people running older kernels don't get a nasty surprise when they upgrade their hardware (and use -cpu host).

One more thing to watch out for. We also need to see if there aren't more mistakes like that out there.

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

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