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@xxxxxxxxxx>
Reviewed-by: Andrew Murray <andrew.murray@xxxxxxx>
> ---
> 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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