Patch "xen/events: Mask a moving irq" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

xen/events: Mask a moving irq

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-events-mask-a-moving-irq.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Boris Ostrovsky <[email protected]>
Date: Fri, 18 Mar 2016 10:11:07 -0400
Subject: xen/events: Mask a moving irq

From: Boris Ostrovsky <[email protected]>

commit ff1e22e7a638a0782f54f81a6c9cb139aca2da35 upstream.

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.

---
 drivers/xen/events/events_base.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

@@ -503,9 +503,19 @@ static void eoi_pirq(struct irq_data *da
 	struct physdev_eoi eoi = { .irq = pirq_from_irq(data->irq) };
 	int rc = 0;
 
-	irq_move_irq(data);
+	if (!VALID_EVTCHN(evtchn))
+		return;
 
-	if (VALID_EVTCHN(evtchn))
+	if (unlikely(irqd_is_setaffinity_pending(data))) {
+		int masked = test_and_set_mask(evtchn);
+
+		clear_evtchn(evtchn);
+
+		irq_move_masked_irq(data);
+
+		if (!masked)
+			unmask_evtchn(evtchn);
+	} else
 		clear_evtchn(evtchn);
 
 	if (pirq_needs_eoi(data->irq)) {

@@ -1395,9 +1405,19 @@ static void ack_dynirq(struct irq_data *
 {
 	int evtchn = evtchn_from_irq(data->irq);
 
-	irq_move_irq(data);
+	if (!VALID_EVTCHN(evtchn))
+		return;
 
-	if (VALID_EVTCHN(evtchn))
+	if (unlikely(irqd_is_setaffinity_pending(data))) {
+		int masked = test_and_set_mask(evtchn);
+
+		clear_evtchn(evtchn);
+
+		irq_move_masked_irq(data);
+
+		if (!masked)
+			unmask_evtchn(evtchn);
+	} else
 		clear_evtchn(evtchn);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/xen-events-mask-a-moving-irq.patch