Re: [PATCH v3 7/9] arm/arm64: kvm: pmu: Make overflow handler NMI safe

From: Mark Rutland <mark.rutland@arm.com>
To: Julien Thierry <julien.thierry@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Pouloze <suzuki.poulose@arm.com>,
	peterz@infradead.org, liwei391@huawei.com, will.deacon@arm.com,
	Christoffer Dall <christoffer.dall@arm.com>,
	acme@kernel.org, alexander.shishkin@linux.intel.com,
	mingo@redhat.com, James Morse <james.morse@arm.com>,
	namhyung@kernel.org, jolsa@redhat.com,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 7/9] arm/arm64: kvm: pmu: Make overflow handler NMI safe
Date: Mon, 8 Jul 2019 16:30:57 +0100	[thread overview]
Message-ID: <20190708153057.GC36116@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <1562596377-33196-8-git-send-email-julien.thierry@arm.com>

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 <julien.thierry@arm.com>
> Cc: Christoffer Dall <christoffer.dall@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Suzuki K Pouloze <suzuki.poulose@arm.com>
> Cc: kvmarm@lists.cs.columbia.edu
> ---
>  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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