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From:   Oliver Upton <oliver.upton@linux.dev>
To:     Raghavendra Rao Ananta <rananta@google.com>
Cc:     Eric Auger <eauger@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Shaoqin Huang <shahuang@redhat.com>,
        Jing Zhang <jingzhangos@google.com>,
        Reiji Watanabe <reijiw@google.com>,
        Colton Lewis <coltonlewis@google.com>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and
 PMOVS{SET,CLR} on vCPU reset
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On Wed, Oct 18, 2023 at 02:16:36PM -0700, Raghavendra Rao Ananta wrote:

[...]

> I had a brief discussion about this with Oliver, and it looks like we
> might need a couple of additional changes for these register accesses:
> - For the userspace accesses, we have to implement explicit get_user
> and set_user callbacks that to filter out the unimplemented counters
> using kvm_pmu_valid_counter_mask().
> - For the guest accesses to be correct, we might have to apply the
> same mask while serving KVM_REQ_RELOAD_PMU.

To be precise, the second issue is that we want to make sure KVM's PMU
emulation never uses an invalid value for the configuration, like
enabling a PMC at an index inaccessible to the guest.

-- 
Thanks,
Oliver