xenbus: use virt_xxx barriers

drivers/xen/xenbus/xenbus_comms.c uses
full memory barriers to communicate with the other side.

For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
would be sufficient, so mb() and wmb() here are only needed if
a non-SMP guest runs on an SMP host.

Switch to virt_xxx barriers which serve this exact purpose.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index fdb0f33..ecdecce 100644 (file)
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len)
                        avail = len;
 
                /* Must write data /after/ reading the consumer index. */
-               mb();
+               virt_mb();
 
                memcpy(dst, data, avail);
                data += avail;
                len -= avail;
 
                /* Other side must not see new producer until data is there. */
-               wmb();
+               virt_wmb();
                intf->req_prod += avail;
 
                /* Implies mb(): other side will see the updated producer. */
@@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len)
                        avail = len;
 
                /* Must read data /after/ reading the producer index. */
-               rmb();
+               virt_rmb();
 
                memcpy(data, src, avail);
                data += avail;
                len -= avail;
 
                /* Other side must not see free space until we've copied out */
-               mb();
+               virt_mb();
                intf->rsp_cons += avail;
 
                pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);