A follow-up patch will require certain write to happen before an event channel is unmasked.
While the memory barrier is not strictly necessary for all the callers, the main one will need it. In order to avoid an extra memory barrier when using fifo event channels, mandate evtchn_unmask() to provide write ordering.
The 2-level event handling unmask operation is missing an appropriate barrier, so add it. Fifo event channels are fine in this regard due to using sync_cmpxchg().
This is part of XSA-332.
This is upstream commit 4d3fe31bd993ef504350989786858aefdb877daa
Cc: stable@vger.kernel.org Suggested-by: Julien Grall julien@xen.org Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Julien Grall jgrall@amazon.com Reviewed-by: Wei Liu wl@xen.org --- drivers/xen/events/events_2l.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/xen/events/events_2l.c b/drivers/xen/events/events_2l.c index 8edef51c92e5..e4b75693600e 100644 --- a/drivers/xen/events/events_2l.c +++ b/drivers/xen/events/events_2l.c @@ -91,6 +91,8 @@ static void evtchn_2l_unmask(unsigned port)
BUG_ON(!irqs_disabled());
+ smp_wmb(); /* All writes before unmask must be visible. */ + if (unlikely((cpu != cpu_from_evtchn(port)))) do_hypercall = 1; else {