linux-kernel - Re: [PATCH v8 04/13] KVM: arm64: PMU: Set PMCR_EL0.N for vCPU based on the associated PMU

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Message-ID: <d6721a96-ddbb-6cf9-0fed-6fc754982ffe@redhat.com>
Date:   Mon, 23 Oct 2023 18:20:05 +0200 (CEST)
From:   Sebastian Ott <sebott@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
cc:     Oliver Upton <oliver.upton@...ux.dev>,
        Marc Zyngier <maz@...nel.org>,
        Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Shaoqin Huang <shahuang@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 04/13] KVM: arm64: PMU: Set PMCR_EL0.N for vCPU based
 on the associated PMU

On Fri, 20 Oct 2023, Raghavendra Rao Ananta wrote:
> The number of PMU event counters is indicated in PMCR_EL0.N.
> For a vCPU with PMUv3 configured, the value is set to the same
> value as the current PE on every vCPU reset.  Unless the vCPU is
> pinned to PEs that has the PMU associated to the guest from the
> initial vCPU reset, the value might be different from the PMU's
> PMCR_EL0.N on heterogeneous PMU systems.
>
> Fix this by setting the vCPU's PMCR_EL0.N to the PMU's PMCR_EL0.N
> value. Track the PMCR_EL0.N per guest, as only one PMU can be set
> for the guest (PMCR_EL0.N must be the same for all vCPUs of the
> guest), and it is convenient for updating the value.
>
> To achieve this, the patch introduces a helper,
> kvm_arm_pmu_get_max_counters(), that reads the maximum number of
> counters from the arm_pmu associated to the VM. Make the function
> global as upcoming patches will be interested to know the value
> while setting the PMCR.N of the guest from userspace.
>
> KVM does not yet support userspace modifying PMCR_EL0.N.
> The following patch will add support for that.
>
> Signed-off-by: Reiji Watanabe <reijiw@...gle.com>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>

Reviewed-by: Sebastian Ott <sebott@...hat.com>