linux-kernel - Re: [PATCH v7 06/12] KVM: arm64: PMU: Add a helper to read the number of counters

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Date:   Fri, 13 Oct 2023 13:24:52 -0700
From:   Raghavendra Rao Ananta <rananta@...gle.com>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     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 06/12] KVM: arm64: PMU: Add a helper to read the number
 of counters

Hi Oliver,

On Thu, Oct 12, 2023 at 10:43 PM Oliver Upton <oliver.upton@...ux.dev> wrote:
>
> On Tue, Oct 10, 2023 at 10:30:31PM +0000, Oliver Upton wrote:
> > On Mon, Oct 09, 2023 at 11:08:52PM +0000, Raghavendra Rao Ananta wrote:
> > > Add a helper, kvm_arm_get_num_counters(), to read the 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.
> > >
> > > Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> > > ---
> > >  arch/arm64/kvm/pmu-emul.c | 17 +++++++++++++++++
> > >  include/kvm/arm_pmu.h     |  6 ++++++
> > >  2 files changed, 23 insertions(+)
> > >
> > > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> > > index a161d6266a5c..84aa8efd9163 100644
> > > --- a/arch/arm64/kvm/pmu-emul.c
> > > +++ b/arch/arm64/kvm/pmu-emul.c
> > > @@ -873,6 +873,23 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
> > >     return true;
> > >  }
> > >
> > > +/**
> > > + * kvm_arm_get_num_counters - Get the number of general-purpose PMU counters.
> > > + * @kvm: The kvm pointer
> > > + */
> > > +int kvm_arm_get_num_counters(struct kvm *kvm)
> >
> > nit: the naming suggests this returns the configured number of PMCs, not
> > the limit.
> >
> > Maybe kvm_arm_pmu_get_max_counters()?
>
Sure, kvm_arm_pmu_get_max_counters() it is!

> Following up on the matter -- please try to avoid sending patches that
> add helpers without any users. Lifting *existing* logic into a helper
> and updating the callsites is itself worthy of a separate patch. But
> adding a new function called by nobody doesn't do much, and can easily
> be squashed into the patch that consumes the new logic.
>
Sounds good. I'll squash patches of this type into the caller patches.

Thank you.
Raghavendra
> --
> Thanks,
> Oliver