xen/events: use virt_xxx barriers

PATCH In review Michael S. Tsirkin 3 participants 5 messages Jan 4, 2016 Xen hypervisor interface

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Michael S. Tsirkin

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2016-01-04 11:46 UTC #0 lore raw

PATCH 1/1 xen/events: use virt_xxx barriers

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.

Signed-off-by Michael S. Tsirkin <[email protected]>

---

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(-)

drivers/xen/events/events_fifo.c +2 -1

index 96a1b8d..eff2b88 100644
@@ -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];
 	}

Signature · 1 line

MST

David Vrabel

Acked-by on v1 1/1

2016-01-04 11:47 UTC #1 lore raw

Quoted 9 lines · 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.

Thanks!

Acked-by David Vrabel <[email protected]>

David

David Vrabel

Acked-by on v1 1/1

2016-01-04 11:47 UTC #2 lore raw

In reply to Michael S. Tsirkin

Quoted 9 lines · 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.

Thanks!

Acked-by David Vrabel <[email protected]>

David

kbuild test robot

build bot

2016-01-04 11:57 UTC #3 lore raw

In reply to Michael S. Tsirkin

reproduce:

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

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kbuild test robot

build bot

2016-01-04 11:57 UTC #4 lore raw

In reply to Michael S. Tsirkin

reproduce:

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