On Thu, 31 Dec 2015, Michael S. Tsirkin wrote:
> 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@xxxxxxxxxx>
Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> include/xen/interface/io/ring.h | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
> index 7dc685b..21f4fbd 100644
> --- a/include/xen/interface/io/ring.h
> +++ b/include/xen/interface/io/ring.h
> @@ -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)
>
> --
> MST
>
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