Marc, I assume that you will take a look at this from the KVM side. :)
On Mon, Jul 08, 2019 at 03:32:55PM +0100, Julien Thierry wrote:
> When using an NMI for the PMU interrupt, taking any lock migh cause a
> deadlock. The current PMU overflow handler in KVM takes takes locks when
> trying to wake up a vcpu.
>
> When overflow handler is called by an NMI, defer the vcpu waking in an
> irq_work queue.
>
> Signed-off-by: Julien Thierry <[email protected]>
> Cc: Christoffer Dall <[email protected]>
> Cc: Marc Zyngier <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Mark Rutland <[email protected]>
> Cc: James Morse <[email protected]>
> Cc: Suzuki K Pouloze <[email protected]>
> Cc: [email protected]
> ---
> include/kvm/arm_pmu.h | 1 +
> virt/kvm/arm/pmu.c | 25 ++++++++++++++++++++++++-
> 2 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 16c769a..8202ed7 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -27,6 +27,7 @@ struct kvm_pmu {
> bool ready;
> bool created;
> bool irq_level;
> + struct irq_work overflow_work;
> };
>
> #define kvm_arm_pmu_v3_ready(v) ((v)->arch.pmu.ready)
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 3dd8238..63f358e 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -421,6 +421,22 @@ void kvm_pmu_sync_hwstate(struct kvm_vcpu *vcpu)
> }
>
> /**
> + * When perf interrupt is an NMI, we cannot safely notify the vcpu
> corresponding
> + * to the even.
Nit: s/even/event/
Thanks,
Mark.
> + * This is why we need a callback to do it once outside of the NMI context.
> + */
> +static void kvm_pmu_perf_overflow_notify_vcpu(struct irq_work *work)
> +{
> + struct kvm_vcpu *vcpu;
> + struct kvm_pmu *pmu;
> +
> + pmu = container_of(work, struct kvm_pmu, overflow_work);
> + vcpu = kvm_pmc_to_vcpu(&pmu->pmc[0]);
> +
> + kvm_vcpu_kick(vcpu);
> +}
> +
> +/**
> * When the perf event overflows, set the overflow status and inform the
> vcpu.
> */
> static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
> @@ -435,7 +451,11 @@ static void kvm_pmu_perf_overflow(struct perf_event
> *perf_event,
>
> if (kvm_pmu_overflow_status(vcpu)) {
> kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> - kvm_vcpu_kick(vcpu);
> +
> + if (!in_nmi())
> + kvm_vcpu_kick(vcpu);
> + else
> + irq_work_queue(&vcpu->arch.pmu.overflow_work);
> }
> }
>
> @@ -706,6 +726,9 @@ static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu)
> return ret;
> }
>
> + init_irq_work(&vcpu->arch.pmu.overflow_work,
> + kvm_pmu_perf_overflow_notify_vcpu);
> +
> vcpu->arch.pmu.created = true;
> return 0;
> }
> --
> 1.9.1
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