[PATCH] xen/events: Mask a moving irq

[Boris Ostrovsky]

Moving an unmasked irq may result in irq handler being invoked on both
source and target CPUs.

With 2-level this can happen as follows:

On source CPU:
        evtchn_2l_handle_events() ->
            generic_handle_irq() ->
                handle_edge_irq() ->
                   eoi_pirq():
                       irq_move_irq(data);

                       /***** WE ARE HERE *****/

                       if (VALID_EVTCHN(evtchn))
                           clear_evtchn(evtchn);

If at this moment target processor is handling an unrelated event in
evtchn_2l_handle_events()'s loop it may pick up our event since target's
cpu_evtchn_mask claims that this event belongs to it *and* the event is
unmasked and still pending. At the same time, source CPU will continue
executing its own handle_edge_irq().

With FIFO interrupt the scenario is similar: irq_move_irq() may result
in a EVTCHNOP_unmask hypercall which, in turn, may make the event
pending on the target CPU.

We can avoid this situation by moving and clearing the event while
keeping event masked.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 drivers/xen/events/events_base.c |   26 ++++++++++++++++++++++++--
 1 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 524c221..c5725ee 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -483,12 +483,23 @@ static void eoi_pirq(struct irq_data *data)
 	int evtchn = evtchn_from_irq(data->irq);
 	struct physdev_eoi eoi = { .irq = pirq_from_irq(data->irq) };
 	int rc = 0;
+	int need_unmask = 0;
 
-	irq_move_irq(data);
+	if (unlikely(irqd_is_setaffinity_pending(data))) {
+		if (VALID_EVTCHN(evtchn))
+			need_unmask = !test_and_set_mask(evtchn);
+	}
 
 	if (VALID_EVTCHN(evtchn))
 		clear_evtchn(evtchn);
 
+	irq_move_irq(data);
+
+	if (VALID_EVTCHN(evtchn)) {
+		if (unlikely(need_unmask))
+			unmask_evtchn(evtchn);
+	}
+
 	if (pirq_needs_eoi(data->irq)) {
 		rc = HYPERVISOR_physdev_op(PHYSDEVOP_eoi, &eoi);
 		WARN_ON(rc);
@@ -1356,11 +1367,22 @@ static void disable_dynirq(struct irq_data *data)
 static void ack_dynirq(struct irq_data *data)
 {
 	int evtchn = evtchn_from_irq(data->irq);
+	int need_unmask = 0;
 
-	irq_move_irq(data);
+	if (unlikely(irqd_is_setaffinity_pending(data))) {
+		if (VALID_EVTCHN(evtchn))
+			need_unmask = !test_and_set_mask(evtchn);
+	}
 
 	if (VALID_EVTCHN(evtchn))
 		clear_evtchn(evtchn);
+
+	irq_move_irq(data);
+
+	if (VALID_EVTCHN(evtchn)) {
+		if (unlikely(need_unmask))
+			unmask_evtchn(evtchn);
+	}
 }
 
 static void mask_ack_dynirq(struct irq_data *data)
-- 
1.7.7.6