Re: [Xen-devel] [PATCH v6 18/29] xen/x86: allow disabling the emulated pmu

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/25/2015 11:22 AM, Roger Pau Monné wrote:
> El 25/09/15 a les 17.13, Jan Beulich ha escrit:
> > > > > On 25.09.15 at 17:07, <roger.pau@xxxxxxxxxx> wrote:
> > > El 21/09/15 a les 16.48, Boris Ostrovsky ha escrit:
> > > > On 09/21/2015 10:36 AM, Jan Beulich wrote:
> > > > > > > > On 04.09.15 at 14:08, <roger.pau@xxxxxxxxxx> wrote:
> > > > > Hmm - this seems questionable to me: Isn't the vPMU an optional
> > > > > feature anyway? I.e. doesn't need separate handling here? Boris?
> > > > It is optional system-wise, not per-guest, which is what I think Roger
> > > > is trying to do. I in fact wanted to add ability to disable VPMU per
> > > > guest myself.
> > > >
> > > > However, VPMU has nothing to do with device model so I don't think it
> > > > should be part of this series from that perspective.
> > > vpmu is enabled globally on the xen command line, there's no way to
> > > disable it on a per-guest basis, so AFAICS it will be enabled for
> > > HMVlite guests which is wrong because we don't have a vlapic.
> > Hmm, Boris specifically enabled vPMU to be available to all three
> > kinds of guests, and PVH in it s current shape doesn't have a
> > vLAPIC either. So making such a connection seems wrong to me.
> IMHO, I would prefer the vPMU support in HVMlite guests to be tied to a
> vlapic presence, so we can do it the HVM way instead of having to do
> hypercalls.
>
> One think that could work is changing the is_hvm_* calls in vpmu.c to
> has_vlapic. This way HVMlite guests could still use the PV vPMU
> interface, but once a lapic is enabled we could use the native way.
Yes, I think that would work.

-boris


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