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

To: Jan Beulich <jbeulich@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen: mask XSAVE in cpuid since we don'tallow guests to use it
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 09 Mar 2009 11:45:00 +0000
Cc: Boris Derzhavets <bderzhavets@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Marc - A. Dahlhaus \[ Administration | Westermann GmbH \]" <mad@xxxxxx>
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Thread-topic: [Xen-devel] Re: [PATCH] xen: mask XSAVE in cpuid since we don'tallow guests to use it
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On 09/03/2009 11:31, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> 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.

Well, it makes the difference between working but without the new feature,
versus quite possibly simply not working at all (and failing in rare and
subtle ways, perhaps). Isn't one obviously better than the other?

 -- Keir

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