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Commit 506b02eb authored Dec 27, 2015 by Michael S. Tsirkin

xen/io: use virt_xxx barriers



include/xen/interface/io/ring.h 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>

parent 5bb0c9be

include/xen/interface/io/ring.h

+8 −8

Original line number	Diff line number	Diff line
		@@ -208,12 +208,12 @@ struct __name##_back_ring { \


		#define RING_PUSH_REQUESTS(_r) do { \
		wmb(); /* back sees requests /before/ updated producer index */ \
		virt_wmb(); /* back sees requests /before/ updated producer index */ \
		(_r)->sring->req_prod = (_r)->req_prod_pvt; \
		} while (0)

		#define RING_PUSH_RESPONSES(_r) do { \
		wmb(); /* front sees responses /before/ updated producer index */ \
		virt_wmb(); /* front sees responses /before/ updated producer index */ \
		(_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
		} while (0)

		@@ -250,9 +250,9 @@ struct __name##_back_ring { \
		#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
		RING_IDX __old = (_r)->sring->req_prod; \
		RING_IDX __new = (_r)->req_prod_pvt; \
		wmb(); /* back sees requests /before/ updated producer index */ \
		virt_wmb(); /* back sees requests /before/ updated producer index */ \
		(_r)->sring->req_prod = __new; \
		mb(); /* back sees new requests /before/ we check req_event */ \
		virt_mb(); /* back sees new requests /before/ we check req_event */ \
		(_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
		(RING_IDX)(__new - __old)); \
		} while (0)
		@@ -260,9 +260,9 @@ struct __name##_back_ring { \
		#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
		RING_IDX __old = (_r)->sring->rsp_prod; \
		RING_IDX __new = (_r)->rsp_prod_pvt; \
		wmb(); /* front sees responses /before/ updated producer index */ \
		virt_wmb(); /* front sees responses /before/ updated producer index */ \
		(_r)->sring->rsp_prod = __new; \
		mb(); /* front sees new responses /before/ we check rsp_event */ \
		virt_mb(); /* front sees new responses /before/ we check rsp_event */ \
		(_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
		(RING_IDX)(__new - __old)); \
		} while (0)
		@@ -271,7 +271,7 @@ struct __name##_back_ring { \
		(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
		if (_work_to_do) break; \
		(_r)->sring->req_event = (_r)->req_cons + 1; \
		mb(); \
		virt_mb(); \
		(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
		} while (0)

		@@ -279,7 +279,7 @@ struct __name##_back_ring { \
		(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
		if (_work_to_do) break; \
		(_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
		mb(); \
		virt_mb(); \
		(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
		} while (0)