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    SubjectRe: [PATCH v3 15/16] kvm: x86: ioapic: Lazy update IOAPIC EOI
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    On 13/09/19 21:01, Suthikulpanit, Suravee wrote:
    > /*
    > + * In case APICv accelerate EOI write and do not trap,
    > + * in-kernel IOAPIC will not be able to receive the EOI.
    > + * In this case, we do lazy update of the pending EOI when
    > + * trying to set IOAPIC irq.
    > + */
    > + if (kvm_apicv_eoi_accelerate(ioapic->kvm, edge))
    > + ioapic_lazy_update_eoi(ioapic, irq);
    > +

    This is okay for the RTC, and in fact I suggest that you make it work
    like this even for Intel. This will get rid of kvm_apicv_eoi_accelerate
    and be nicer overall.

    However, it cannot work for the in-kernel PIT, because it is currently
    checking ps->irq_ack before kvm_set_irq. Unfortunately, the in-kernel
    PIT is relying on the ack notifier to timely queue the pt->worker work
    item and reinject the missed tick.

    Thus, you cannot enable APICv if ps->reinject is true.

    Perhaps you can make kvm->arch.apicv_state a disabled counter? Then
    Hyper-V can increment it when enabled, PIT can increment it when
    ps->reinject becomes true and decrement it when it becomes false;
    finally, svm.c can increment it when an SVM guest is launched and
    increment/decrement it around ExtINT handling?

    (This conflicts with some of the suggestions I made earlier, which
    implied the existence of apicv_state, but everything should if anything
    become easier).

    Paolo

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