IB/core, RDMA RW API: Do not exceed QP SGE send limit

Compute the SGE limit for RDMA READ and WRITE requests in
ib_create_qp(). Use that limit in the RDMA RW API implementation.
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Steve Wise <swise@opengridcomputing.com>
Cc: Parav Pandit <pandit.parav@gmail.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: <stable@vger.kernel.org> #v4.7+
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/rw.c

@@ -58,13 +58,6 @@ static inline bool rdma_rw_io_needs_mr(struct ib_device *dev, u8 port_num,
 	return false;
 }
 
-static inline u32 rdma_rw_max_sge(struct ib_device *dev,
-		enum dma_data_direction dir)
-{
-	return dir == DMA_TO_DEVICE ?
-		dev->attrs.max_sge : dev->attrs.max_sge_rd;
-}
-
 static inline u32 rdma_rw_fr_page_list_len(struct ib_device *dev)
 {
 	/* arbitrary limit to avoid allocating gigantic resources */
@@ -186,7 +179,8 @@ static int rdma_rw_init_map_wrs(struct rdma_rw_ctx *ctx, struct ib_qp *qp,
 		u64 remote_addr, u32 rkey, enum dma_data_direction dir)
 {
 	struct ib_device *dev = qp->pd->device;
-	u32 max_sge = rdma_rw_max_sge(dev, dir);
+	u32 max_sge = dir == DMA_TO_DEVICE ? qp->max_write_sge :
+		      qp->max_read_sge;
 	struct ib_sge *sge;
 	u32 total_len = 0, i, j;
 

drivers/infiniband/core/verbs.c

@@ -814,6 +814,15 @@ struct ib_qp *ib_create_qp(struct ib_pd *pd,
 		}
 	}
 
+	/*
+	 * Note: all hw drivers guarantee that max_send_sge is lower than
+	 * the device RDMA WRITE SGE limit but not all hw drivers ensure that
+	 * max_send_sge <= max_sge_rd.
+	 */
+	qp->max_write_sge = qp_init_attr->cap.max_send_sge;
+	qp->max_read_sge = min_t(u32, qp_init_attr->cap.max_send_sge,
+				 device->attrs.max_sge_rd);
+
 	return qp;
 }
 EXPORT_SYMBOL(ib_create_qp);

include/rdma/ib_verbs.h

@@ -1428,6 +1428,10 @@ struct ib_srq {
 	} ext;
 };
 
+/*
+ * @max_write_sge: Maximum SGE elements per RDMA WRITE request.
+ * @max_read_sge:  Maximum SGE elements per RDMA READ request.
+ */
 struct ib_qp {
 	struct ib_device       *device;
 	struct ib_pd	       *pd;
@@ -1449,6 +1453,8 @@ struct ib_qp {
 	void                  (*event_handler)(struct ib_event *, void *);
 	void		       *qp_context;
 	u32			qp_num;
+	u32			max_write_sge;
+	u32			max_read_sge;
 	enum ib_qp_type		qp_type;
 };