Commit 1491937f authored Mar 18, 2016 by Boris Ostrovsky Committed by Sasha Levin Apr 20, 2016

xen/events: Mask a moving irq



[ Upstream commit ff1e22e7a638a0782f54f81a6c9cb139aca2da35 ]

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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent bdd37003

drivers/xen/events/events_base.c

+24 −4

Original line number	Diff line number	Diff line
		@@ -483,9 +483,19 @@ 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)) {
		@@ -1360,9 +1370,19 @@ 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);
		}