[PATCH] xen/events: use virt_xxx barriers

[PATCH] xen/events: use virt_xxx barriers

[Michael S. Tsirkin]

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>
---

This is on top of my series:
	arch: barrier cleanup + barriers for virt
and will be included in v3 of the series.

 drivers/xen/events/events_fifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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];
 	}
 
-- 
MST

Re: [PATCH] xen/events: use virt_xxx barriers

[David Vrabel]

On 04/01/16 11:46, 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.

Thanks!

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

David

Re: [PATCH] xen/events: use virt_xxx barriers

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1336 bytes --]

Hi Michael,

[auto build test ERROR on v4.4-rc8]
[also build test ERROR on next-20151231]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Michael-S-Tsirkin/xen-events-use-virt_xxx-barriers/20160104-194916
config: x86_64-randconfig-x008-01040711 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   drivers/xen/events/events_fifo.c: In function 'consume_one_event':
>> drivers/xen/events/events_fifo.c:300:3: error: implicit declaration of function 'virt_rmb' [-Werror=implicit-function-declaration]
      virt_rmb(); /* Ensure word is up-to-date before reading head. */
      ^
   cc1: some warnings being treated as errors

vim +/virt_rmb +300 drivers/xen/events/events_fifo.c

   294	
   295		/*
   296		 * Reached the tail last time?  Read the new HEAD from the
   297		 * control block.
   298		 */
   299		if (head == 0) {
 > 300			virt_rmb(); /* Ensure word is up-to-date before reading head. */
   301			head = control_block->head[priority];
   302		}
   303	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 21830 bytes --]