[Xen-devel] [PATCH v2 30/32] virtio_ring: update weak barriers to use __smp_xxx

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

virtio ring uses smp_wmb on SMP and wmb on !SMP,
the reason for the later being that it might be
talking to another kernel on the same SMP machine.

This is exactly what __smp_XXX barriers do,
so switch to these instead of homegrown ifdef hacks.

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 include/linux/virtio_ring.h | 25 ++++---------------------
 1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 67e06fe..f3fa55b 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -12,7 +12,7 @@
  * anyone care?
  *
  * For virtio_pci on SMP, we don't need to order with respect to MMIO
- * accesses through relaxed memory I/O windows, so smp_mb() et al are
+ * accesses through relaxed memory I/O windows, so virt_mb() et al are
  * sufficient.
  *
  * For using virtio to talk to real devices (eg. other heterogeneous
@@ -21,11 +21,10 @@
  * actually quite cheap.
  */
 
-#ifdef CONFIG_SMP
 static inline void virtio_mb(bool weak_barriers)
 {
        if (weak_barriers)
-               smp_mb();
+               virt_mb();
        else
                mb();
 }
@@ -33,7 +32,7 @@ static inline void virtio_mb(bool weak_barriers)
 static inline void virtio_rmb(bool weak_barriers)
 {
        if (weak_barriers)
-               smp_rmb();
+               virt_rmb();
        else
                rmb();
 }
@@ -41,26 +40,10 @@ static inline void virtio_rmb(bool weak_barriers)
 static inline void virtio_wmb(bool weak_barriers)
 {
        if (weak_barriers)
-               smp_wmb();
+               virt_wmb();
        else
                wmb();
 }
-#else
-static inline void virtio_mb(bool weak_barriers)
-{
-       mb();
-}
-
-static inline void virtio_rmb(bool weak_barriers)
-{
-       rmb();
-}
-
-static inline void virtio_wmb(bool weak_barriers)
-{
-       wmb();
-}
-#endif
 
 struct virtio_device;
 struct virtqueue;
-- 
MST

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