IB/mlx5: Avoid system crash when enabling many VFs

When enabling many VFs, the total amount of DMA mappings increase
significantly. This causes DMA allocations to take a lot of time
since they are serialized in the kernel.

As a result the driver enters into fatal condition due to
timeout and the system hangs. To recover from this we disable
MR cache for VFs.

PFs will still have a full cache and VFs cache can be manipulated
as usual after driver load.

Fixes: e126ba9 ('mlx5: Add driver for Mellanox Connect-IB adapters')
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/mr.c

@@ -627,7 +627,8 @@ int mlx5_mr_cache_init(struct mlx5_ib_dev *dev)
 		ent->order = i + 2;
 		ent->dev = dev;
 
-		if (dev->mdev->profile->mask & MLX5_PROF_MASK_MR_CACHE)
+		if ((dev->mdev->profile->mask & MLX5_PROF_MASK_MR_CACHE) &&
+		    (mlx5_core_is_pf(dev->mdev)))
 			limit = dev->mdev->profile->mr_cache[i].limit;
 		else
 			limit = 0;