xen/events: Mask a moving irq

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@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 24 insertions, 4 deletions

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 488017a0806a..cb7138c97c69 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -484,9 +484,19 @@ static void eoi_pirq(struct irq_data *data)
         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)) {
@@ -1357,9 +1367,19 @@ static void ack_dynirq(struct irq_data *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);
 }