Re: [PATCH v7 5/7] KVM: arm64: pmu: Make overflow handler NMI safe

[Will Deacon]

On Thu, Sep 24, 2020 at 12:07:04PM +0100, Alexandru Elisei wrote:
> From: Julien Thierry <julien.thierry@xxxxxxx>
> 
> kvm_vcpu_kick() is not NMI safe. When the overflow handler is called from
> NMI context, defer waking the vcpu to an irq_work queue.
> 
> A vcpu can be freed while it's not running by kvm_destroy_vm(). Prevent
> running the irq_work for a non-existent vcpu by calling irq_work_sync() on
> the PMU destroy path.
> 
> Cc: Julien Thierry <julien.thierry.kdev@xxxxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Suzuki K Pouloze <suzuki.poulose@xxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
> Tested-by: Sumit Garg <sumit.garg@xxxxxxxxxx> (Developerbox)
> [Alexandru E.: Added irq_work_sync()]
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
> I suggested in v6 that I will add an irq_work_sync() to
> kvm_pmu_vcpu_reset(). It turns out it's not necessary: a vcpu reset is done
> by the vcpu being reset with interrupts enabled, which means all the work
> has had a chance to run before the reset takes place.

I don't understand this ^^

But the patch itself looks good, so I'm going to queue this lot anyway!

Will