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, 37 insertions, 8 deletions

diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index 184abd5f493c..3856ee3854f6 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -1231,7 +1231,7 @@ int mlx5_mr_cache_init(struct mlx5_ib_dev *dev);
 int mlx5_mr_cache_cleanup(struct mlx5_ib_dev *dev);
 
 struct mlx5_ib_mr *mlx5_mr_cache_alloc(struct mlx5_ib_dev *dev,
-				       unsigned int entry);
+				       unsigned int entry, int access_flags);
 void mlx5_mr_cache_free(struct mlx5_ib_dev *dev, struct mlx5_ib_mr *mr);
 int mlx5_mr_cache_invalidate(struct mlx5_ib_mr *mr);
 
@@ -1444,25 +1444,54 @@ int bfregn_to_uar_index(struct mlx5_ib_dev *dev,
 			struct mlx5_bfreg_info *bfregi, u32 bfregn,
 			bool dyn_bfreg);
 
-static inline bool mlx5_ib_can_use_umr(struct mlx5_ib_dev *dev,
-				       bool do_modify_atomic, int access_flags)
+static inline bool mlx5_ib_can_load_pas_with_umr(struct mlx5_ib_dev *dev,
+						 size_t length)
 {
+	/*
+	 * umr_check_mkey_mask() rejects MLX5_MKEY_MASK_PAGE_SIZE which is
+	 * always set if MLX5_IB_SEND_UMR_UPDATE_TRANSLATION (aka
+	 * MLX5_IB_UPD_XLT_ADDR and MLX5_IB_UPD_XLT_ENABLE) is set. Thus, a mkey
+	 * can never be enabled without this capability. Simplify this weird
+	 * quirky hardware by just saying it can't use PAS lists with UMR at
+	 * all.
+	 */
 	if (MLX5_CAP_GEN(dev->mdev, umr_modify_entity_size_disabled))
 		return false;
 
-	if (do_modify_atomic &&
+	/*
+	 * length is the size of the MR in bytes when mlx5_ib_update_xlt() is
+	 * used.
+	 */
+	if (!MLX5_CAP_GEN(dev->mdev, umr_extended_translation_offset) &&
+	    length >= MLX5_MAX_UMR_PAGES * PAGE_SIZE)
+		return false;
+	return true;
+}
+
+/*
+ * true if an existing MR can be reconfigured to new access_flags using UMR.
+ * Older HW cannot use UMR to update certain elements of the MKC. See
+ * umr_check_mkey_mask(), get_umr_update_access_mask() and umr_check_mkey_mask()
+ */
+static inline bool mlx5_ib_can_reconfig_with_umr(struct mlx5_ib_dev *dev,
+						 unsigned int current_access_flags,
+						 unsigned int target_access_flags)
+{
+	unsigned int diffs = current_access_flags ^ target_access_flags;
+
+	if ((diffs & IB_ACCESS_REMOTE_ATOMIC) &&
 	    MLX5_CAP_GEN(dev->mdev, atomic) &&
 	    MLX5_CAP_GEN(dev->mdev, umr_modify_atomic_disabled))
 		return false;
 
-	if (access_flags & IB_ACCESS_RELAXED_ORDERING &&
+	if ((diffs & IB_ACCESS_RELAXED_ORDERING) &&
 	    MLX5_CAP_GEN(dev->mdev, relaxed_ordering_write) &&
 	    !MLX5_CAP_GEN(dev->mdev, relaxed_ordering_write_umr))
 		return false;
 
-	if (access_flags & IB_ACCESS_RELAXED_ORDERING &&
-	     MLX5_CAP_GEN(dev->mdev, relaxed_ordering_read) &&
-	     !MLX5_CAP_GEN(dev->mdev, relaxed_ordering_read_umr))
+	if ((diffs & IB_ACCESS_RELAXED_ORDERING) &&
+	    MLX5_CAP_GEN(dev->mdev, relaxed_ordering_read) &&
+	    !MLX5_CAP_GEN(dev->mdev, relaxed_ordering_read_umr))
 		return false;
 
 	return true;