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

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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>
This commit is contained in:
Roman Kagan 2017-07-20 17:26:40 +03:00 committed by Radim Krčmář
parent f244deed7a
commit f1ff89ec44
1 changed files with 4 additions and 3 deletions
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7
arch/x86/kvm/hyperv.c
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@ -649,9 +649,10 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
}
if ((stimer->config & HV_STIMER_ENABLE) &&
stimer->count)
stimer_start(stimer);
else
stimer->count) {
if (!stimer->msg_pending)
stimer_start(stimer);
} else
stimer_cleanup(stimer);
}
}