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Re: [Xen-devel] [PATCH] xen: mask XSAVE in cpuid since we don't allowgue

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: mask XSAVE in cpuid since we don't allowguests to use it
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Mon, 09 Mar 2009 11:26:33 +0000
Cc: Boris Derzhavets <bderzhavets@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Marc - A. Dahlhaus \[ Administration | Westermann GmbH \]" <mad@xxxxxx>
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>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 08.03.09 06:31 >>>
>Mask X86_FEATURE_XSAVE in cpuid leaf 1, ecx, as we don't allow guests to
>use it (by setting cr4.OSXSAVE).

I actually disagree to this. The kernel should be dealing with the situation
by inspecting the OSXSAVE bit in CPUID when running under Xen, since it's
really Xen that's the 'OS' for that particular feature.

Then, once Keir gets willing to take Intel xsave patch(es), no further change
is going to be needed here. And the same kernel will work (assuming it has
no other dependencies) on older Xen not having this bit masked.


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