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authorRusty Russell <rusty@rustcorp.com.au>2013-03-18 13:22:19 +1030
committerRusty Russell <rusty@rustcorp.com.au>2013-03-20 14:00:41 +1030
commita9a0fef779074838230e04a322fd2bdc921f4f4f (patch)
treea7d25b5002e84ac3df54788ec2620ccc1f7c2c21 /include/linux/virtio_ring.h
parent73640c991e2f2804939af70567b23e4c54b7c266 (diff)
virtio_ring: expose virtio barriers for use in vringh.
The host side of ring needs this logic too. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'include/linux/virtio_ring.h')
-rw-r--r--include/linux/virtio_ring.h57
1 files changed, 57 insertions, 0 deletions
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 63c6ea199519..ca3ad41c2c82 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -4,6 +4,63 @@
#include <linux/irqreturn.h>
#include <uapi/linux/virtio_ring.h>
+/*
+ * Barriers in virtio are tricky. Non-SMP virtio guests can't assume
+ * they're not on an SMP host system, so they need to assume real
+ * barriers. Non-SMP virtio hosts could skip the barriers, but does
+ * 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
+ * sufficient.
+ *
+ * For using virtio to talk to real devices (eg. other heterogeneous
+ * CPUs) we do need real barriers. In theory, we could be using both
+ * kinds of virtio, so it's a runtime decision, and the branch is
+ * actually quite cheap.
+ */
+
+#ifdef CONFIG_SMP
+static inline void virtio_mb(bool weak_barriers)
+{
+ if (weak_barriers)
+ smp_mb();
+ else
+ mb();
+}
+
+static inline void virtio_rmb(bool weak_barriers)
+{
+ if (weak_barriers)
+ smp_rmb();
+ else
+ rmb();
+}
+
+static inline void virtio_wmb(bool weak_barriers)
+{
+ if (weak_barriers)
+ smp_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;