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Subject: Re: [Xen-devel] [PATCH v2 2/3] x86 Test and expose CPUID faulting
 capabilities in /proc/cpuinfo
To: Kyle Huey <me@kylehuey.com>, Jan Beulich <JBeulich@suse.com>
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Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        DaveHansen <dave.hansen@linux.intel.com>,
        Huang Rui <ray.huang@amd.com>,
        Kristen Carlson Accardi <kristen@linux.intel.com>,
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        <linux-kernel@vger.kernel.org>,
        Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date: Thu, 15 Sep 2016 15:41:13 -0400
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On 09/15/2016 03:11 PM, Kyle Huey wrote:
> On Thu, Sep 15, 2016 at 3:25 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 15.09.16 at 12:05, <david.vrabel@citrix.com> wrote:
>>> On 14/09/16 22:01, Kyle Huey wrote:
>>>> Xen advertises the underlying support for CPUID faulting but not does pass
>>>> through writes to the relevant MSR, nor does it virtualize it, so it does
>>>> not actually work. For now mask off the relevant bit on MSR_PLATFORM_INFO.
>>> Could you clarify in the commit message that it is PV guests that are
>>> affected.
>> What makes you think HVM ones aren't?
> Testing on EC2, HVM guests are affected as well.  Not sure what to do
> about that.

You could clear capability bit in xen_set_cpu_features() but of course
this assumes you will never again read MSR_PLATFORM_INFO.

-boris