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

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Message-ID: <20101206174852.GG4936@amd.com>
Date:	Mon, 6 Dec 2010 18:48:52 +0100
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Avi Kivity <avi@...hat.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 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.

	Joerg

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