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xen/events: Mask a moving irq

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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>
This commit is contained in:
Boris Ostrovsky 2016-03-18 10:11:07 -04:00 committed by David Vrabel
parent 85d1a29de8
commit ff1e22e7a6
1 changed files with 24 additions and 4 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

28
drivers/xen/events/events_base.c
View file

@ -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);
}