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

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

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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