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[Xen-devel] Re: [PATCH] xen: mask XSAVE in cpuid since we don'tallow gue

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] xen: mask XSAVE in cpuid since we don'tallow guests to use it
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Mon, 09 Mar 2009 11:31:02 +0000
Cc: Boris Derzhavets <bderzhavets@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Marc - A. Dahlhaus \[ Administration | Westermann GmbH \]" <mad@xxxxxx>
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>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 08.03.09 10:13 >>>
>On 08/03/2009 05:31, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:
>> Mask X86_FEATURE_XSAVE in cpuid leaf 1, ecx, as we don't allow guests to
>> use it (by setting cr4.OSXSAVE).
>> This prevents crashes in pvops dom0 kernels, as new versions of Linux try
>> to use this feature.
>> (This patch deals with dom0 cpuid; I'm not sure where the right place to
>> set up the default mask for domU is.)
>Thanks, the whole problem stems from blacklisting rather than whitelisting
>feature bits. I might try and do a more comprehensive job for xen-unstable
>at least. This is good for 3.3.

I'm not sure whitelisting will be much better than blacklisting - while now
any feature requiring not-yet-implemented support in Xen must be turned
off explicitly, this would just turn over to requiring explicitly un-hiding any
new feature not requiring Xen's intervention. A real solution to this issue
would require some assistance from the hardware vendors I'd think.


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