Re: [PATCH v7] arm/kvm: Enable support for KVM_ARM_VCPU_PMU_V3_FILTER

[Daniel P . Berrangé]

On Tue, Mar 19, 2024 at 03:00:40PM +0000, Peter Maydell wrote:
> On Tue, 19 Mar 2024 at 14:57, Eric Auger <eauger@redhat.com> wrote:
> >
> > Hi Peter,
> >
> > On 2/29/24 12:00, Peter Maydell wrote:
> > >
> > > It doesn't appear because the list of properties that we advertise
> > > via query-cpu-model-expansion is set in the 
> > > cpu_model_advertised_features[]
> > > array in target/arm/arm-qmp-cmds.c, and this patch doesn't add
> > > 'kvm-pmu-filter' to it. But you have a good point about all the
> > > others being bool properties: I don't know enough about that
> > > mechanism to know if simply adding this to the list is right.
> > >
> > > This does raise a more general question: do we need to advertise
> > > the existence of this property to libvirt via QMP? Eric, Sebastian:
> > > do you know ?
> > sorry I missed this question. yes I think it is sensible to expose that
> > option to libvirt. There is no good default value to be set at qemu
> > level so to me it really depends on the upper stack to choose the
> > correct value (depending on the sensitiveness of the data that justified
> > the kernel uapi).
> 
> In that case we should definitely have a mechanism for libvirt
> to be able to say "does this QEMU (and this CPU) implement
> this property?". Unfortunately my QMP/libvirt expertise is
> too low to be able to suggest what that mechanism should be...

Libvirt uses 'qom-list' on '/machine/unattached/device[0]' to
identify CPU properties.

If 'kvm-pmu-filter' appears with that, then detection will be
fine.

With regards,
Daniel
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