From: Andrew Murray <andrew.murray@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/4] KVM: arm64: pmu: Set the CHAINED attribute before creating the in-kernel event
Date: Fri, 11 Oct 2019 15:19:34 +0100 [thread overview]
Message-ID: <20191011141933.GQ42880@e119886-lin.cambridge.arm.com> (raw)
In-Reply-To: <20191011123954.31378-4-maz@kernel.org>
On Fri, Oct 11, 2019 at 01:39:53PM +0100, Marc Zyngier wrote:
> The current convention for KVM to request a chained event from the
> host PMU is to set bit[0] in attr.config1 (PERF_ATTR_CFG1_KVM_PMU_CHAINED).
>
> But as it turns out, this bit gets set *after* we create the kernel
> event that backs our virtual counter, meaning that we never get
> a 64bit counter.
>
> Moving the setting to an earlier point solves the problem.
>
> Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
> ---
> virt/kvm/arm/pmu.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index c30c3a74fc7f..f291d4ac3519 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -569,12 +569,12 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
> * high counter.
> */
> attr.sample_period = (-counter) & GENMASK(63, 0);
> + if (kvm_pmu_counter_is_enabled(vcpu, pmc->idx + 1))
> + attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
> +
> event = perf_event_create_kernel_counter(&attr, -1, current,
> kvm_pmu_perf_overflow,
> pmc + 1);
> -
> - if (kvm_pmu_counter_is_enabled(vcpu, pmc->idx + 1))
> - attr.config1 |= PERF_ATTR_CFG1_KVM_PMU_CHAINED;
> } else {
> /* The initial sample period (overflow count) of an event. */
> if (kvm_pmu_idx_is_64bit(vcpu, pmc->idx))
> --
> 2.20.1
>
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next prev parent reply other threads:[~2019-10-11 14:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-11 12:39 [PATCH v3 0/4] KVM: arm64: Assorted PMU emulation fixes Marc Zyngier
2019-10-11 12:39 ` [PATCH v3 1/4] KVM: arm64: pmu: Fix cycle counter truncation Marc Zyngier
2019-10-11 12:39 ` [PATCH v3 2/4] arm64: KVM: Handle PMCR_EL0.LC as RES1 on pure AArch64 systems Marc Zyngier
2019-10-11 12:39 ` [PATCH v3 3/4] KVM: arm64: pmu: Set the CHAINED attribute before creating the in-kernel event Marc Zyngier
2019-10-11 14:19 ` Andrew Murray [this message]
2019-10-11 12:39 ` [PATCH v3 4/4] KVM: arm64: pmu: Reset sample period on overflow handling Marc Zyngier
2019-10-15 10:00 ` Andrew Murray
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