Re: [PATCH v8 0/7] KVM: arm64: PMU: Use multiple host PMUs

[Oliver Upton <oupton@kernel.org>]

On Tue, Jul 07, 2026 at 08:58:50AM +0100, Marc Zyngier wrote:
> On Mon, 06 Jul 2026 19:28:20 +0100,
> Oliver Upton <oupton@kernel.org> wrote:
> > 
> > On Mon, Jul 06, 2026 at 07:03:23PM +0900, Akihiko Odaki wrote:
> > > Akihiko Odaki (7):
> > >       KVM: arm64: Disallow vPMU when pPMUs do not cover all CPUs
> > >       KVM: arm64: PMU: Protect the list of PMUs with RCU
> > >       KVM: arm64: PMU: Pass the pPMU to kvm_map_pmu_event()
> > >       KVM: arm64: PMU: Pass the target CPU to kvm_pmu_probe_armpmu()
> > >       KVM: arm64: PMU: Implement fixed-counters-only emulation
> > >       KVM: arm64: PMU: Introduce FIXED_COUNTERS_ONLY
> > >       KVM: arm64: selftests: Test PMU_V3_FIXED_COUNTERS_ONLY
> > 
> > Thanks for respinning the series, I left some comments. I'd really like
> > to get this feature picked up, hope you have cycles to work on it soon.
> > 
> > FWIW, we're considering adding a new vCPU feature flag to deprecate all
> > the ugliness of the old PMUv3 UAPI. I'm tempted to say that the
> > FIXED_COUNTERS_ONLY feature is conditioned on the new feature flag...
> 
> It'd be good to have a strawman proposal on the list if we are going
> to change add a new API, specially if this is likely to gate new code.
> 

Patch 1 [*] of the series I linked does exactly this, no? Needs some
attention like a KVM_CAP to make the bit discoverable by the VMM but
gets the general idea across.

[*]: https://lore.kernel.org/kvmarm/20260702190421.420992-2-congkai@amazon.com/

Thanks,
Oliver