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

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Message-ID: <Z2c6l1cTM7V1Jy7V@linux.dev>
Date: Sat, 21 Dec 2024 14:00:55 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: Janne Grunau <j@...nau.net>
Cc: kvmarm@...ts.linux.dev, Marc Zyngier <maz@...nel.org>,
	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>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	asahi@...ts.linux.dev
Subject: Re: [PATCH 00/18] KVM: arm64: Support FEAT_PMUv3 on Apple hardware

On Sat, Dec 21, 2024 at 02:45:49PM +0100, Janne Grunau wrote:
> On Tue, Dec 17, 2024 at 01:20:30PM -0800, Oliver Upton wrote:
> > One of the interesting features of some Apple M* parts is an IMPDEF trap
> > that routes EL1/EL0 accesses of the PMUv3 registers to EL2. This allows
> > a hypervisor to emulate an architectural PMUv3 on top of the IMPDEF PMU
> > hardware present in the CPU.
> > 
> > And if you squint, this _might_ look like a CPU erratum :-)
> > 
> > This series takes advantage of these IMPDEF traps to provide PMUv3 to
> > KVM guests. As a starting point, only expose the fixed CPU cycle counter
> > and no event counters. Conveniently, this is enough to get Windows
> > running as a KVM guest on Apple hardware.
> > 
> > I've tried to keep the deviation to a minimum by refactoring some of the
> > flows used for PMUv3, e.g. computing PMCEID from the arm_pmu bitmap
> > instead of reading hardware directly.
> > 
> > RFC -> v1:
> >  - Rebase to 6.13-rc3
> >  - Add support for 1 event counter in addition to CPU cycle counter
> >  - Don't sneak past the PMU event filter (Marc)
> >  - Have the PMU driver provide a PMUv3 -> HW event ID mapping (Marc)
> > 
> > Tested on my M2 with Linux and Windows guests. If possible, I'd
> > appreciate someone testing on an M1 as I haven't added those MIDRs to
> > the erratum yet.
> 
> Tested on M1 (t8103) with perf in a Linux guest and the patch below
> 
> Tested-by: Janne Grunau <j@...nau.net>
> 
> I'll import this into the downstream asahi kernel as there was a request
> for performance counters to aid FEX-Emu development recently.
> 
> Janne

Awesome, greatly appreciate the testing Janne. Hopefully we can get this
worked out for upstream too :)

-- 
Thanks,
Oliver