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    SubjectRe: [PATCH v3 21/26] KVM: SVM: Drop AVIC's intermediate avic_set_running() helper
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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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