Re: [PATCH 0/3] KVM: arm64: nv: Add EL2 PMU event filtering support

[Marc Zyngier <maz@kernel.org>]

On Sat, 24 Aug 2024 01:13:59 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> We allow a nested VM to be configured with a vPMU, although it isn't
> entirely functional. We do not currently respect the EL2 event filter
> configuration from the guest hypervisor, which really needs to be
> applied to EL1 when in a hyp context.
> 
> Series to do just that. Tested on Neoverse-V2 which fortunately
> implements PMUv3 and NV, unlike the fruity stuff I'm typically using...
> 
> Oliver Upton (3):
>   KVM: arm64: Add helpers to determine if PMC counts at a given EL
>   KVM: arm64: nv: Honor NSH filter when in hyp context
>   KVM: arm64: nv: Reprogram PMU events affected by nested transition
> 
>  arch/arm64/kvm/emulate-nested.c |  4 ++
>  arch/arm64/kvm/pmu-emul.c       | 77 ++++++++++++++++++++++++++++-----
>  include/kvm/arm_pmu.h           |  3 ++
>  3 files changed, 72 insertions(+), 12 deletions(-)
> 
> 
> base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba

I had a quick look, and definitely like the way it is shaping up (it
does the job without fuss, and NV isn't about performance anyway).

However, I think it needs a bit more work so that MDCR_EL2.HPMN is
correctly handled. This shouldn't be hard to do, and if FEAT_FGT is
supported in the guest, then we could even expose FEAT_HPMN0 (though I
haven't worked out yet why FGT is a dependency).

With that, I think we could take it in.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.