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From: Andrew Murray <andrew.murray@arm.com>
To: Julien Thierry <julien.thierry@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v9 4/5] KVM: arm/arm64: remove pmc->bitmask
Date: Thu, 13 Jun 2019 10:39:57 +0100
Message-ID: <20190613093957.GG49779@e119886-lin.cambridge.arm.com> (raw)
In-Reply-To: <6a8e4fdd-d8cf-f3fb-55cd-2d06805b0eb9@arm.com>

On Thu, Jun 13, 2019 at 08:30:51AM +0100, Julien Thierry wrote:
> Hi Andrew,
> 
> On 12/06/2019 20:04, Andrew Murray wrote:
> > We currently use pmc->bitmask to determine the width of the pmc - however
> > it's superfluous as the pmc index already describes if the pmc is a cycle
> > counter or event counter. The architecture clearly describes the widths of
> > these counters.
> > 
> > Let's remove the bitmask to simplify the code.
> > 
> > Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> > ---
> >  include/kvm/arm_pmu.h |  1 -
> >  virt/kvm/arm/pmu.c    | 19 +++++++++----------
> >  2 files changed, 9 insertions(+), 11 deletions(-)
> > 
> > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> > index b73f31baca52..2f0e28dc5a9e 100644
> > --- a/include/kvm/arm_pmu.h
> > +++ b/include/kvm/arm_pmu.h
> > @@ -28,7 +28,6 @@
> >  struct kvm_pmc {
> >  	u8 idx;	/* index into the pmu->pmc array */
> >  	struct perf_event *perf_event;
> > -	u64 bitmask;
> >  };
> >  
> >  struct kvm_pmu {
> > diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> > index ae1e886d4a1a..88ce24ae0b45 100644
> > --- a/virt/kvm/arm/pmu.c
> > +++ b/virt/kvm/arm/pmu.c
> > @@ -47,7 +47,10 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
> >  		counter += perf_event_read_value(pmc->perf_event, &enabled,
> >  						 &running);
> >  
> > -	return counter & pmc->bitmask;
> > +	if (select_idx != ARMV8_PMU_CYCLE_IDX)
> > +		counter = lower_32_bits(counter);
> 
> Shouldn't this depend on PMCR.LC as well? If PMCR.LC is clear we only
> want the lower 32bits of the cycle counter.

Yes that's correct. The hunk should look like this:

-       return counter & pmc->bitmask;
+       if (!(select_idx == ARMV8_PMU_CYCLE_IDX &&
+             __vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_LC))
+               counter = lower_32_bits(counter);
+
+       return counter;

Thanks for the review.

Andrew Murray

> 
> Cheers,
> 
> -- 
> Julien Thierry
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Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 19:04 [PATCH v9 0/5] KVM: arm/arm64: add support for chained counters Andrew Murray
2019-06-12 19:04 ` [PATCH v9 1/5] KVM: arm/arm64: rename kvm_pmu_{enable/disable}_counter functions Andrew Murray
2019-06-12 19:04 ` [PATCH v9 2/5] KVM: arm/arm64: extract duplicated code to own function Andrew Murray
2019-06-12 19:04 ` [PATCH v9 3/5] KVM: arm/arm64: re-create event when setting counter value Andrew Murray
2019-06-12 19:04 ` [PATCH v9 4/5] KVM: arm/arm64: remove pmc->bitmask Andrew Murray
2019-06-13  7:30   ` Julien Thierry
2019-06-13  9:39     ` Andrew Murray [this message]
2019-06-13 16:50       ` Suzuki K Poulose
2019-06-17 15:43         ` Andrew Murray
2019-06-17 16:33           ` Suzuki K Poulose
2019-06-17 18:06             ` Andrew Murray
2019-06-12 19:04 ` [PATCH v9 5/5] KVM: arm/arm64: support chained PMU counters Andrew Murray
2019-06-14 12:08   ` Suzuki K Poulose

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