[PATCH v2 4/5] xen/events: unmask a fifo event channel only if it was masked

Juergen Gross
2020-10-22T09:49:13Z

Unmasking an event channel with fifo events channels being used can
require a hypercall to be made, so try to avoid that by checking
whether the event channel was really masked.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V2:
- move test for already unmasked into loop (Jan Beulich)
---
drivers/xen/events/events_fifo.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 243e7b6d7b96..b234f1766810 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -237,6 +237,9 @@ static bool clear_masked_cond(volatile event_word_t *word)
w = *word;

do {
+ if (!(w & (1 << EVTCHN_FIFO_MASKED)))
+ return true;
+
if (w & (1 << EVTCHN_FIFO_PENDING))
return false;

--
2.26.2