linux-kernel - 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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Date:   Thu, 19 Oct 2023 13:17:58 -0700
From:   Raghavendra Rao Ananta <rananta@...gle.com>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     Eric Auger <eauger@...hat.com>, 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 v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and
 PMOVS{SET,CLR} on vCPU reset

On Thu, Oct 19, 2023 at 12:06 PM Oliver Upton <oliver.upton@...ux.dev> 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 PM Raghavendra Rao Ananta
> > <rananta@...gle.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 planned.

Thank you.
Raghavendra

> --
> Thanks,
> Oliver