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RE: [Xen-devel] [PATCH] X86: cpuid faulting feature enable

To: Keir Fraser <keir.xen@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] X86: cpuid faulting feature enable
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Sat, 2 Jul 2011 11:04:30 +0800
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Thread-topic: [Xen-devel] [PATCH] X86: cpuid faulting feature enable
> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx]
> Sent: Saturday, July 02, 2011 12:08 AM
> On 01/07/2011 16:48, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> >> + if ( cpuid_faulting_flip )
> >> + {
> >> +  unsigned int enable;
> >> +
> >> +  enable = !is_hvm_vcpu(next) && (next->domain->domain_id != 0);
> >
> > Excluding Dom0 here is perhaps questionable (as it could allow hiding
> > features not supported by Xen from applications).
> It's probably because of a need for raw cpuid in libxc/xc_cpuid_x86.c where
> we need to detect things like long mode. We could do that another way, or
> provide a new paravirtualised raw cpuid just for dom0.
> Not a barrier to this patch going in imo.
> I suppose HVM VCPUs are excluded because otherwise the new feature would
> be
> unexpectedly enabled in non-root mode too, and make HVM guests crash? :-)

yes, unless we convert GP to cause VM-exit as an alternative. :-)


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