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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>
This commit is contained in:
Michael S. Tsirkin 2015-12-27 18:02:16 +02:00
parent 788e5b3a5d
commit 5bb0c9be2a
1 changed files with 4 additions and 4 deletions
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8
drivers/xen/xenbus/xenbus_comms.c
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@ -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);