From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: [PATCH] X86: cpuid faulting feature enable
Date: Fri, 01 Jul 2011 17:07:52 +0100
Message-ID: <CA33AF68.1D5C3%keir.xen@gmail.com>
References: <4E0E088A020000780004BB07@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@novell.com>, Jinsong Liu <jinsong.liu@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Haitao Shan <haitao.shan@intel.com>, Xin Li <xin.li@intel.com>
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On 01/07/2011 16:48, "Jan Beulich" <JBeulich@novell.com> 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? :-)

 -- Keir