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From:   Raghavendra Rao Ananta <rananta@google.com>
Date:   Thu, 19 Oct 2023 13:17:58 -0700
Message-ID: <CAJHc60yNfGo8A+RLozgEsDO=75SQAB5dswAWgFzc3OS7_3FfKQ@mail.gmail.com>
Subject: Re: [PATCH v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and
 PMOVS{SET,CLR} on vCPU reset
To:     Oliver Upton <oliver.upton@linux.dev>
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
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On Thu, Oct 19, 2023 at 12:06=E2=80=AFPM Oliver Upton <oliver.upton@linux.d=
ev> wrote:
>
> Hi Raghu,
>
> Can you please make sure you include leading and trailing whitespace for
> your inline replies? The message gets extremely dense and is difficult
> to read.
>
> Also -- delete any unrelated context from your replies. If there's a
> localized conversation about a particular detail there's no reason to
> keep the entire thread in the body.
>
Sorry about that. I'll try to keep it clean.

> On Thu, Oct 19, 2023 at 11:46:22AM -0700, Raghavendra Rao Ananta wrote:
> > On Wed, Oct 18, 2023 at 2:16=E2=80=AFPM Raghavendra Rao Ananta
> > <rananta@google.com> 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().
> > Re-thinking the first case: Since these registers go through a reset
> > (reset_pmu_reg()) during initialization, where the valid counter mask
> > is applied, and since we are sanitizing the registers with the mask
> > before running the guest (below case), will implementing the
> > {get,set}_user() add any value, apart from just keeping userspace in
> > sync with every update of PMCR.N?
>
> KVM's sysreg emulation (as seen from userspace) fails to uphold the RES0
> bits of these registers. That's a bug.
>
Got it. Thanks for the confirmation. I'll implement these as originally pla=
nned.

Thank you.
Raghavendra

> --
> Thanks,
> Oliver