[v3,39/41] xen/events: use virt_xxx barriers
diff mbox

Message ID 1452426622-4471-40-git-send-email-mst@redhat.com
State New, archived
Headers show

Commit Message

Michael S. Tsirkin Jan. 10, 2016, 2:21 p.m. UTC
drivers/xen/events/events_fifo.c uses rmb() to communicate with the
other side.

For guests compiled with CONFIG_SMP, smp_rmb would be sufficient, so
rmb() here is only needed if a non-SMP guest runs on an SMP host.

Switch to the virt_rmb barrier which serves this exact purpose.

Pull in asm/barrier.h here to make sure the file is self-contained.

Suggested-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/xen/events/events_fifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

David Vrabel Jan. 11, 2016, 11:12 a.m. UTC | #1
On 10/01/16 14:21, Michael S. Tsirkin wrote:
> drivers/xen/events/events_fifo.c uses rmb() to communicate with the
> other side.
> 
> For guests compiled with CONFIG_SMP, smp_rmb would be sufficient, so
> rmb() here is only needed if a non-SMP guest runs on an SMP host.
> 
> Switch to the virt_rmb barrier which serves this exact purpose.
> 
> Pull in asm/barrier.h here to make sure the file is self-contained.
> 
> Suggested-by: David Vrabel <david.vrabel@citrix.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Acked-by: David Vrabel <david.vrabel@citrix.com>

David

Patch
diff mbox

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 96a1b8d..eff2b88 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -41,6 +41,7 @@ 
 #include <linux/percpu.h>
 #include <linux/cpu.h>
 
+#include <asm/barrier.h>
 #include <asm/sync_bitops.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
@@ -296,7 +297,7 @@  static void consume_one_event(unsigned cpu,
 	 * control block.
 	 */
 	if (head == 0) {
-		rmb(); /* Ensure word is up-to-date before reading head. */
+		virt_rmb(); /* Ensure word is up-to-date before reading head. */
 		head = control_block->head[priority];
 	}