From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [Patch 2/4] Refining Xsave/Xrestore support
Date: Wed, 27 Oct 2010 10:12:30 -0700
Message-ID: <4CC85D7E.2010201@goop.org>
References: <AANLkTimWUuyHvZ06=2cRBhvw2fcfMzA5QAuJZJso7=gY@mail.gmail.com>
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To: Haitao Shan <maillists.shan@gmail.com>
Cc: xen-devel@lists.xensource.com, "Han, Weidong" <weidong.han@intel.com>, Keir Fraser <keir.fraser@eu.citrix.com>
List-Id: xen-devel@lists.xenproject.org

 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