From ba0f96f9c509753fdb3d3644e875b794d893e4e8 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 7 Sep 2020 15:47:27 +0200 Subject: [PATCH 01/12] xen/events: add a proper barrier to 2-level uevent unmasking 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. Cc: stable@vger.kernel.org Reported-by: Julien Grall Suggested-by: Julien Grall Signed-off-by: Juergen Gross Reviewed-by: Julien Grall Reviewed-by: Wei Liu --- 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 64df919a2111..e1af5e093ff4 100644 --- a/drivers/xen/events/events_2l.c +++ b/drivers/xen/events/events_2l.c @@ -91,6 +91,8 @@ static void evtchn_2l_unmask(evtchn_port_t 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 { -- 2.26.2