On 25/11/2020 10:51, Juergen Gross wrote:
evtchn_fifo_set_pending() can be simplified a little bit.
The commit message is quite light... For posterity, it would be good to
explain why the simplication can be done. In particular, there is a
chance in behavior after this patch.
Suggested-by: Jan Beulich <jbeul...@suse.com>
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
V8:
- new patch
---
xen/common/event_fifo.c | 34 +++++++++++++++-------------------
1 file changed, 15 insertions(+), 19 deletions(-)
diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c
index 443593c3b3..77609539b1 100644
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -175,6 +175,18 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct
evtchn *evtchn)
return;
}
+ /*
+ * Control block not mapped. The guest must not unmask an
+ * event until the control block is initialized, so we can
+ * just drop the event.
+ */
+ if ( unlikely(!v->evtchn_fifo->control_block) )
Sort of unrelated, AFAICT, v->evtchn_fifo->control_block can be set
concurrently to this access.
Thankfully, once the control block is mapped, it can't be unmapped.
However, there is still a possibility that you may see half of the update.
Shouldn't the field access with ACCESS_ONCE()?
Cheers,
--
Julien Grall
