Messages in this thread | | | Date | Wed, 8 Dec 2021 15:43:19 +0100 | Subject | Re: [PATCH v3 21/26] KVM: SVM: Drop AVIC's intermediate avic_set_running() helper | From | Paolo Bonzini <> |
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On 12/8/21 02:52, Sean Christopherson wrote: > + /* > + * Unload the AVIC when the vCPU is about to block,_before_ the vCPU > + * actually blocks. The vCPU needs to be marked IsRunning=0 before the > + * final pass over the vIRR via kvm_vcpu_check_block(). Any IRQs that > + * arrive before IsRunning=0 will not signal the doorbell, i.e. it's > + * KVM's responsibility to ensure there are no pending IRQs in the vIRR > + * after IsRunning is cleared, prior to scheduling out the vCPU.
I prefer to phrase this around paired memory barriers and the usual store/smp_mb/load lockless idiom:
/* * Unload the AVIC when the vCPU is about to block, _before_ * the vCPU actually blocks. * * Any IRQs that arrive before IsRunning=0 will not cause an * incomplete IPI vmexit on the source, therefore vIRR will also * be checked by kvm_vcpu_check_block() before blocking. The * memory barrier implicit in set_current_state orders writing * IsRunning=0 before reading the vIRR. The processor needs a * matching memory barrier on interrupt delivery between writing * IRR and reading IsRunning; the lack of this barrier might be * the cause of errata #1235). */
Is there any nuance that I am missing?
Paolo
> + */ > + avic_vcpu_put(vcpu); > +
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