linux-kernel - Re: [PATCH] KVM: SVM: Add xsetbv intercept

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Date:	Tue, 07 Dec 2010 11:34:33 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: SVM: Add xsetbv intercept

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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