Re: [Xen-devel] [PATCH] pvcpuid: mask TSC invariant bit for various circumstances

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Yes, CPUID is always trapped for HVM guests.

 -- Keir

On 28/10/2009 16:50, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> Hmmm... this could be a real problem for some apps!
> 
> Is this only a problem for PV domains?  I.e, is cpuid
> always trapped by Xen for HVM domains?
> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx]
>> Sent: Wednesday, October 28, 2009 10:39 AM
>> To: Keir Fraser; Xen-Devel (E-mail); Dan Magenheimer
>> Subject: RE: [Xen-devel] [PATCH] pvcpuid: mask TSC invariant bit for
>> various circumstances
>> 
>>>>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 28.10.09 17:27 >>>
>>> But, that said, I'm still not convinced my patch is the
>>> right answer.  If possible (e.g. using the CPUID masking
>>> feature Jan referred to), Xen should always hide the TSC
>> 
>> Actually I just realized that this feature would probably not help you
>> at all: The bit you're after is in leaf 0x80000007, but the
>> masking applies
>> only to leaf 1 (plus 0x80000001 for AMD).
>> 
>>> Invariant bit from all guests (OS's and apps) and only
>>> expose it via pvcpuid or some other mechanism.
>>> Otherwise an OS or app may make false assumptions
>>> based on an architecturally-specified cpuid bit.
>>  
>> Jan
>> 
>> 



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