linux-kernel - Re: [PATCH 00/18] KVM: arm64: Support FEAT

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Message-ID: <87jzb5q9nl.wl-maz@kernel.org>
Date: Wed, 08 Jan 2025 21:26:54 +0000
From: Marc Zyngier <maz@...nel.org>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Will Deacon <will@...nel.org>,
	kvmarm@...ts.linux.dev,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Mingwei Zhang <mizhang@...gle.com>,
	Colton Lewis <coltonlewis@...gle.com>,
	Raghavendra Rao Ananta <rananta@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/18] KVM: arm64: Support FEAT_PMUv3 on Apple hardware

On Wed, 08 Jan 2025 20:14:07 +0000,
Oliver Upton <oliver.upton@...ux.dev> wrote:
> 
> Hey Will,
> 
> On Wed, Jan 08, 2025 at 12:38:41PM +0000, Will Deacon wrote:
> > What's your plan for this series? I started looking at it and I can take
> > the first four apple_m1 patches if you like?
> 
> I plan on posting a respin of it by next week, which should look pretty
> much the same besides cleaning up the build error I introduced :)
> 
> Besides that, I think we need to decide on the KVM side of things
> whether or not we want to support an event counter in addition to the
> PMU cycle counter. Janne's FEX use case would certainly benefit from it.

I think we should always be able to support *one* counter on top of
the cycle counter. Doing more than that would result in inconsistent
behaviours (some events only count on a single counter).

Unless we restrict ourselves to a very small set of events that we can
always schedule on any counter, but this doesn't sound very promising.

Thoughts?

	M.

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