RDMA/mlx5: Clarify what the UMR is for when creating MRs

Once a mkey is created it can be modified using UMR. This is desirable for
performance reasons. However, different hardware has restrictions on what
modifications are possible using UMR. Make sense of these checks:

- mlx5_ib_can_reconfig_with_umr() returns true if the access flags can be
  altered. Most cases create MRs using 0 access flags (now made clear by
  consistent use of set_mkc_access_pd_addr_fields()), but the old logic
  here was tormented. Make it clear that this is checking if the current
  access_flags can be modified using UMR to different access_flags. It is
  always OK to use UMR to change flags that all HW supports.

- mlx5_ib_can_load_pas_with_umr() returns true if UMR can be used to
  enable and update the PAS/XLT. Enabling requires updating the entity
  size, so UMR ends up completely disabled on this old hardware. Make it
  clear why it is disabled. FRWR, ODP and cache always requires
  mlx5_ib_can_load_pas_with_umr().

- mlx5_ib_pas_fits_in_mr() is used to tell if an existing MR can be
  resized to hold a new PAS list. This only works for cached MR's because
  we don't store the PAS list size in other cases.

To be very clear, arrange things so any pre-created MR's in the cache
check the newly requested access_flags before allowing the MR to leave the
cache. If UMR cannot set the required access_flags the cache fails to
create the MR.

This in turn means relaxed ordering and atomic are now correctly blocked
early for implicit ODP on older HW.

Link: https://lore.kernel.org/r/20200914112653.345244-6-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 14 insertions, 13 deletions

diff --git a/drivers/infiniband/hw/mlx5/wr.c b/drivers/infiniband/hw/mlx5/wr.c
index 43880973a512..d6038fb6c50c 100644
--- a/drivers/infiniband/hw/mlx5/wr.c
+++ b/drivers/infiniband/hw/mlx5/wr.c
@@ -398,7 +398,8 @@ static void set_linv_mkey_seg(struct mlx5_mkey_seg *seg)
 	seg->status = MLX5_MKEY_STATUS_FREE;
 }
 
-static void set_reg_mkey_segment(struct mlx5_mkey_seg *seg,
+static void set_reg_mkey_segment(struct mlx5_ib_dev *dev,
+				 struct mlx5_mkey_seg *seg,
 				 const struct ib_send_wr *wr)
 {
 	const struct mlx5_umr_wr *umrwr = umr_wr(wr);
@@ -414,10 +415,12 @@ static void set_reg_mkey_segment(struct mlx5_mkey_seg *seg,
 	MLX5_SET(mkc, seg, rr, !!(umrwr->access_flags & IB_ACCESS_REMOTE_READ));
 	MLX5_SET(mkc, seg, lw, !!(umrwr->access_flags & IB_ACCESS_LOCAL_WRITE));
 	MLX5_SET(mkc, seg, lr, 1);
-	MLX5_SET(mkc, seg, relaxed_ordering_write,
-		 !!(umrwr->access_flags & IB_ACCESS_RELAXED_ORDERING));
-	MLX5_SET(mkc, seg, relaxed_ordering_read,
-		 !!(umrwr->access_flags & IB_ACCESS_RELAXED_ORDERING));
+	if (MLX5_CAP_GEN(dev->mdev, relaxed_ordering_write_umr))
+		MLX5_SET(mkc, seg, relaxed_ordering_write,
+			 !!(umrwr->access_flags & IB_ACCESS_RELAXED_ORDERING));
+	if (MLX5_CAP_GEN(dev->mdev, relaxed_ordering_read_umr))
+		MLX5_SET(mkc, seg, relaxed_ordering_read,
+			 !!(umrwr->access_flags & IB_ACCESS_RELAXED_ORDERING));
 
 	if (umrwr->pd)
 		MLX5_SET(mkc, seg, pd, to_mpd(umrwr->pd)->pdn);
@@ -863,13 +866,11 @@ static int set_reg_wr(struct mlx5_ib_qp *qp,
 	bool atomic = wr->access & IB_ACCESS_REMOTE_ATOMIC;
 	u8 flags = 0;
 
-	if (!mlx5_ib_can_use_umr(dev, atomic, wr->access)) {
-		mlx5_ib_warn(to_mdev(qp->ibqp.device),
-			     "Fast update of %s for MR is disabled\n",
-			     (MLX5_CAP_GEN(dev->mdev,
-					   umr_modify_entity_size_disabled)) ?
-				     "entity size" :
-				     "atomic access");
+	/* Matches access in mlx5_set_umr_free_mkey() */
+	if (!mlx5_ib_can_reconfig_with_umr(dev, 0, wr->access)) {
+		mlx5_ib_warn(
+			to_mdev(qp->ibqp.device),
+			"Fast update for MR access flags is not possible\n");
 		return -EINVAL;
 	}
 
@@ -1263,7 +1264,7 @@ static int handle_qpt_reg_umr(struct mlx5_ib_dev *dev, struct mlx5_ib_qp *qp,
 	*seg += sizeof(struct mlx5_wqe_umr_ctrl_seg);
 	*size += sizeof(struct mlx5_wqe_umr_ctrl_seg) / 16;
 	handle_post_send_edge(&qp->sq, seg, *size, cur_edge);
-	set_reg_mkey_segment(*seg, wr);
+	set_reg_mkey_segment(dev, *seg, wr);
 	*seg += sizeof(struct mlx5_mkey_seg);
 	*size += sizeof(struct mlx5_mkey_seg) / 16;
 	handle_post_send_edge(&qp->sq, seg, *size, cur_edge);