xen/events: mask events when changing their VCPU binding (4704fe4f) · Commits · 戴 / test

When a event is being bound to a VCPU there is a window between the EVTCHNOP_bind_vpcu call and the adjustment of the local per-cpu masks where an event may be lost. The hypervisor upcalls the new VCPU but the kernel thinks that event is still bound to the old VCPU and ignores it. There is even a problem when the event is being bound to the same VCPU as there is a small window beween the clear_bit() and set_bit() calls in bind_evtchn_to_cpu(). When scanning for pending events, the kernel may read the bit when it is momentarily clear and ignore the event. Avoid this by masking the event during the whole bind operation. Signed-off-by:

David Vrabel <david.vrabel@citrix.com> Signed-off-by:

Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by:

Jan Beulich <jbeulich@suse.com> CC: stable@vger.kernel.org

drivers/xen/events.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -1493,8 +1493,10 @@ void rebind_evtchn_irq(int evtchn, int irq)
		/* Rebind an evtchn so that it gets delivered to a specific cpu */
		static int rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
		{
		struct shared_info *s = HYPERVISOR_shared_info;
		struct evtchn_bind_vcpu bind_vcpu;
		int evtchn = evtchn_from_irq(irq);
		int masked;

		if (!VALID_EVTCHN(evtchn))
		return -1;
		@@ -1510,6 +1512,12 @@ static int rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
		bind_vcpu.port = evtchn;
		bind_vcpu.vcpu = tcpu;

		/*
		* Mask the event while changing the VCPU binding to prevent
		* it being delivered on an unexpected VCPU.
		*/
		masked = sync_test_and_set_bit(evtchn, BM(s->evtchn_mask));

		/*
		* If this fails, it usually just indicates that we're dealing with a
		* virq or IPI channel, which don't actually need to be rebound. Ignore
		@@ -1518,6 +1526,9 @@ static int rebind_irq_to_cpu(unsigned irq, unsigned tcpu)
		if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_vcpu, &bind_vcpu) >= 0)
		bind_evtchn_to_cpu(evtchn, tcpu);

		if (!masked)
		unmask_evtchn(evtchn);

		return 0;
		}

Admin message