Re: KVM: IOAPIC: don't clear remote_irr if IRQ is reinjected from EOI

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> There's a bug in the IOAPIC code for level-triggered interrupts. Its
> relatively easy to trigger by sharing (virtio-blk + usbtablet was the
> testcase, initially reported by Gerd von Egidy).
>
> The "remote_irr" variable is used to indicate accepted but not yet acked
> interrupts. Its cleared from the EOI handler.
>
> Problem is that the EOI handler clears remote_irr unconditionally, even
> if it reinjected another pending interrupt.
>
> In that case, kvm_ioapic_set_irq() proceeds to ioapic_service() which
> sets remote_irr even if it failed to inject (since the IRR was high due
> to EOI reinjection).
>
> Since the TMR bit has been cleared by the first EOI, the second one
> fails to clear remote_irr.
>
> End result is interrupt line dead.
>
> Fix it by setting remote_irr only if a new pending interrupt has been
> generated (and the TMR bit for vector in question set).
>   

Applied, thanks.

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