RDMA/mlx5: Disable IB_DEVICE_MEM_MGT_EXTENSIONS if IB_WR_REG_MR can't work

set_reg_wr() always fails if !umr_modify_entity_size_disabled because
mlx5_ib_can_use_umr() always fails. Without set_reg_wr() IB_WR_REG_MR
doesn't work and that means the device should not advertise
IB_DEVICE_MEM_MGT_EXTENSIONS.

Fixes: 841b07f9 ("IB/mlx5: Block MR WR if UMR is not possible")
Link: https://lore.kernel.org/r/20200914112653.345244-5-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/mlx5/main.c

@@ -840,7 +840,9 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
 		/* We support 'Gappy' memory registration too */
 		props->device_cap_flags |= IB_DEVICE_SG_GAPS_REG;
 	}
-	props->device_cap_flags |= IB_DEVICE_MEM_MGT_EXTENSIONS;
+	/* IB_WR_REG_MR always requires changing the entity size with UMR */
+	if (!MLX5_CAP_GEN(dev->mdev, umr_modify_entity_size_disabled))
+		props->device_cap_flags |= IB_DEVICE_MEM_MGT_EXTENSIONS;
 	if (MLX5_CAP_GEN(mdev, sho)) {
 		props->device_cap_flags |= IB_DEVICE_INTEGRITY_HANDOVER;
 		/* At this stage no support for signature handover */