Commit f1ff89ec authored Jul 20, 2017 by Roman Kagan Committed by Radim Krčmář Jul 20, 2017

kvm: x86: hyperv: avoid livelock in oneshot SynIC timers



If the SynIC timer message delivery fails due to SINT message slot being
busy, there's no point to attempt starting the timer again until we're
notified of the slot being released by the guest (via EOM or EOI).

Even worse, when a oneshot timer fails to deliver its message, its
re-arming with an expiration time in the past leads to immediate retry
of the delivery, and so on, without ever letting the guest vcpu to run
and release the slot, which results in a livelock.

To avoid that, only start the timer when there's no timer message
pending delivery.  When there is, meaning the slot is busy, the
processing will be restarted upon notification from the guest that the
slot is released.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

parent f244deed

arch/x86/kvm/hyperv.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -649,9 +649,10 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
		}

		if ((stimer->config & HV_STIMER_ENABLE) &&
		stimer->count)
		stimer->count) {
		if (!stimer->msg_pending)
		stimer_start(stimer);
		else
		} else
		stimer_cleanup(stimer);
		}
		}

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