linux-kernel - Re: [PATCH 1/1] KVM: arm64: PMU: Fix PMCR

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Date:   Sat, 10 Dec 2022 11:16:37 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     James Clark <james.clark@....com>,
        Oliver Upton <oliver.upton@...ux.dev>
Cc:     kvmarm@...ts.linux.dev, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] KVM: arm64: PMU: Fix PMCR_EL0 reset value

On Fri, 09 Dec 2022 17:58:31 +0000,
Oliver Upton <oliver.upton@...ux.dev> wrote:
> 
> On Fri, Dec 09, 2022 at 04:44:46PM +0000, James Clark wrote:
> > ARMV8_PMU_PMCR_N_MASK is an unshifted value which results in the wrong
> > reset value for PMCR_EL0, so shift it to fix it.
> 
> That's just mean. *_MASK tends to be a shifted mask, although it would
> appear that asm/perf_event.h does not follow this convention. Fixing
> that would be nice (as I'm sure somebody else will get burned by this),
> but for the sake of an immediate fix:

Well, that'll teach me the usual lesson: last minute changes without
full non-regression testing are bound to end in disaster.

> 
> > This fixes the following error when running qemu:
> > 
> >   $ qemu-system-aarch64 -cpu host -machine type=virt,accel=kvm -kernel ...
> > 
> >   target/arm/helper.c:1813: pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed.
> > 
> > Fixes: 292e8f149476 ("KVM: arm64: PMU: Simplify PMCR_EL0 reset handling")
> > Signed-off-by: James Clark <james.clark@....com>
> 
> Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>

Thanks both. I'll queue that ASAP as a fix.

	M.

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