Re: [Xen-devel] [PATCH] x86/vpmu: Add get/put_vpmu() and VPMU_ENABLED

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/17/2017 03:28 AM, Jan Beulich wrote:
> > > > On 16.02.17 at 18:31, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 02/16/2017 11:59 AM, Jan Beulich wrote:
> > > Also this new model basically limits the opportunity to change the
> > > mode to the case where no guest at all is running, iiuc. Previously
> > > this would have been possible with any number of guests running,
> > > as long as none of them actually used the vPMU.
> > I don't think much changed. The only difference is that for PV guests we
> > bump vpmu_count at VCPU creation as opposed to during the hypercall.
> >
> > And HVM guests always incremented the count during vcpu_initialise().
> True, so my earlier statement needs to be limited to PV guests.
Which I think is still OK: as long as we promised a guest (via 
CPUID/vpmu_mode at the time of guest creation) that PMU is available we 
shouldn't be able to take it away by changing vpmu_mode, whether or not 
the guest is actually using it.
-boris

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