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Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support
From: Haitao Shan <maillists.shan@xxxxxxxxx>
Date: Thu, 28 Oct 2010 10:57:15 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Han, Weidong" <weidong.han@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Hi, Jeremy,

My approach is based an old PV-OPS kernel source. Kernel tries to set
CR4.OSXSAVE and read it back to determine whether Xsave is actually
Could you still use that?

Shan Haitao

2010/10/28 Jeremy Fitzhardinge <jeremy@xxxxxxxx>:
>  On 10/27/2010 12:04 AM, Haitao Shan wrote:
>> Hi, Keir,
>> This is patch #2, which adds PV guest Xsave support.
> How does a PV guest know whether Xsave support is available?  Previous
> versions of Xen left the xsave cpu feature flag set even though xsave
> wasn't usable by the domain, so I had to forceably mask it from the
> cpuid features within the domain.  Given that a PV domain can't rely on
> X86_FEATURE_XSAVE, how can it tell that the feature is actually usable?
> Thanks,
>    J

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