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

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Message-ID: <20241221134549.GA2917938@robin.jannau.net>
Date: Sat, 21 Dec 2024 14:45:49 +0100
From: Janne Grunau <j@...nau.net>
To: Oliver Upton <oliver.upton@...ux.dev>
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 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

--- 

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 441ee4ffc7709..45ef67ec970f5 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -195,6 +195,12 @@ has_neoverse_n1_erratum_1542419(const struct arm64_cpu_capabilities *entry,
 }

 static const struct midr_range impdef_pmuv3_cpus[] = {
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_ICESTORM),
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_FIRESTORM),
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_ICESTORM_PRO),
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_FIRESTORM_PRO),
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_ICESTORM_MAX),
+	MIDR_ALL_VERSIONS(MIDR_APPLE_M1_FIRESTORM_MAX),
 	MIDR_ALL_VERSIONS(MIDR_APPLE_M2_BLIZZARD),
 	MIDR_ALL_VERSIONS(MIDR_APPLE_M2_AVALANCHE),
 	MIDR_ALL_VERSIONS(MIDR_APPLE_M2_BLIZZARD_PRO),