IB/mlx5: Expose dump and fill memory key

MLX5 IB HCA offers the memory key, dump_fill_mkey to boost
performance, when used in a send or receive operations.

It is used to force local HCA operations to skip the PCI bus access,
while keeping track of the processed length in the ibv_sge handling.

Meaning, instead of a PCI write access the HCA leaves the target
memory untouched, and skips filling that packet section. Similar
behavior is done upon send, the HCA skips data in memory relevant
to this key and saves PCI bus access.

This functionality saves PCI read/write operations.

Signed-off-by: Yonatan Cohen <yonatanc@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Guy Levi <guyle@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/main.c

@@ -1660,6 +1660,7 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 	int err;
 	size_t min_req_v2 = offsetof(struct mlx5_ib_alloc_ucontext_req_v2,
 				     max_cqe_version);
+	u32 dump_fill_mkey;
 	bool lib_uar_4k;
 
 	if (!dev->ib_active)
@@ -1761,6 +1762,12 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 			goto out_uars;
 	}
 
+	if (MLX5_CAP_GEN(dev->mdev, dump_fill_mkey)) {
+		err = mlx5_cmd_dump_fill_mkey(dev->mdev, &dump_fill_mkey);
+		if (err)
+			goto out_td;
+	}
+
 	INIT_LIST_HEAD(&context->vma_private_list);
 	mutex_init(&context->vma_private_list_mutex);
 	INIT_LIST_HEAD(&context->db_page_list);
@@ -1819,6 +1826,15 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 		resp.response_length += sizeof(resp.num_dyn_bfregs);
 	}
 
+	if (field_avail(typeof(resp), dump_fill_mkey, udata->outlen)) {
+		if (MLX5_CAP_GEN(dev->mdev, dump_fill_mkey)) {
+			resp.dump_fill_mkey = dump_fill_mkey;
+			resp.comp_mask |=
+				MLX5_IB_ALLOC_UCONTEXT_RESP_MASK_DUMP_FILL_MKEY;
+		}
+		resp.response_length += sizeof(resp.dump_fill_mkey);
+	}
+
 	err = ib_copy_to_udata(udata, &resp, resp.response_length);
 	if (err)
 		goto out_td;

include/uapi/rdma/mlx5-abi.h

@@ -90,6 +90,7 @@ struct mlx5_ib_alloc_ucontext_req_v2 {
 
 enum mlx5_ib_alloc_ucontext_resp_mask {
 	MLX5_IB_ALLOC_UCONTEXT_RESP_MASK_CORE_CLOCK_OFFSET = 1UL << 0,
+	MLX5_IB_ALLOC_UCONTEXT_RESP_MASK_DUMP_FILL_MKEY    = 1UL << 1,
 };
 
 enum mlx5_user_cmds_supp_uhw {
@@ -138,7 +139,7 @@ struct mlx5_ib_alloc_ucontext_resp {
 	__u32	log_uar_size;
 	__u32	num_uars_per_page;
 	__u32	num_dyn_bfregs;
-	__u32	reserved3;
+	__u32	dump_fill_mkey;
 };
 
 struct mlx5_ib_alloc_pd_resp {