From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH 1/1] KVM: X86: add the support of XSAVE/XRSTOR to guest
Date: Thu, 06 May 2010 22:49:09 +0300
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On 05/06/2010 10:45 PM, Avi Kivity wrote:
>
> All those control registers are annoying, we have cr1 and cr5-cr7 
> free, cr9-cr15 on x86_64, infinite msr space, and now we have XCRs.  
> Great.
>
> Looking forward to YCR0.
>

I think I see the reason - xgetbv is unprivileged, so applications can 
see what the OS supports instead of looking at cpuid and hoping.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.