From: Marc Zyngier <maz@kernel.org>
To: Jing Zhang <jingzhangos@google.com>
Cc: KVM <kvm@vger.kernel.org>, KVMARM <kvmarm@lists.linux.dev>,
ARMLinux <linux-arm-kernel@lists.infradead.org>,
Oliver Upton <oliver.upton@linux.dev>,
Joey Gouly <joey.gouly@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: arm64: Treat ID_AA64DFR0_EL1.PMUVer as an unsigned field
Date: Tue, 21 Apr 2026 17:45:58 +0100 [thread overview]
Message-ID: <86h5p41cu1.wl-maz@kernel.org> (raw)
In-Reply-To: <20260421164112.2448553-1-jingzhangos@google.com>
On Tue, 21 Apr 2026 17:41:12 +0100,
Jing Zhang <jingzhangos@google.com> wrote:
>
> ID_AA64DFR0_EL1.PMUVer is an unsigned 4-bit field, but was historically
> marked as signed in the cpufeature table. This led
> kvm_init_host_debug_data() to fail detection of PMUv3 implementation on
> systems with PMUv3p8 or newer, as the signed extraction of the field
> (e.g., 0b1000 for PMUv3p8) would result in a negative value.
>
> Fix this by marking the field as unsigned in the ftr_id_aa64dfr0 table
> and updating the KVM initialization code to use unsigned extraction.
> While at it, ensure that both the 'Not Implemented' (0b0000) and
> 'Implementation Defined' (0b1111) values are correctly handled as
> indicating the absence of a standard PMUv3.
>
> Signed-off-by: Jing Zhang <jingzhangos@google.com>
https://lore.kernel.org/all/20260305-james-kvm-pmuver-sign-v2-0-ee80a125af9b@linaro.org/
M.
--
Without deviation from the norm, progress is not possible.
prev parent reply other threads:[~2026-04-21 16:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-21 16:41 [PATCH] KVM: arm64: Treat ID_AA64DFR0_EL1.PMUVer as an unsigned field Jing Zhang
2026-04-21 16:45 ` Marc Zyngier [this message]
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