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

Alexandru Elisei alexandru.elisei at arm.com
Wed Sep 30 08:37:49 EDT 2020

Hi Will,

On 9/28/20 6:57 PM, Will Deacon wrote:

> On Thu, Sep 24, 2020 at 12:07:04PM +0100, Alexandru Elisei wrote:
>> From: Julien Thierry <julien.thierry at arm.com>
>> 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 at gmail.com>
>> Cc: Marc Zyngier <marc.zyngier at arm.com>
>> Cc: Will Deacon <will.deacon at arm.com>
>> Cc: Mark Rutland <mark.rutland at arm.com>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: James Morse <james.morse at arm.com>
>> Cc: Suzuki K Pouloze <suzuki.poulose at arm.com>
>> Cc: kvm at vger.kernel.org
>> Cc: kvmarm at lists.cs.columbia.edu
>> Signed-off-by: Julien Thierry <julien.thierry at arm.com>
>> Tested-by: Sumit Garg <sumit.garg at linaro.org> (Developerbox)
>> [Alexandru E.: Added irq_work_sync()]
>> Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
>> ---
>> 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 ^^

Marc had the same comment, I replied in his email. I thought about it and you're
right, it doesn't make much sense.

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

Thank you for picking up the series!


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