IB/mlx5: Use kernel driver to help userspace create ah

Resolving a MAC address for a given IP address in userspace is inefficient.
This patch lets mlx5 user driver using the kernel driver to resolve the mac
and get the answer in the private section of the response.
Signed-off-by: Moni Shoua <monis@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/ah.c

@@ -77,6 +77,27 @@ struct ib_ah *mlx5_ib_create_ah(struct ib_pd *pd, struct ib_ah_attr *ah_attr,
 	if (ll == IB_LINK_LAYER_ETHERNET && !(ah_attr->ah_flags & IB_AH_GRH))
 		return ERR_PTR(-EINVAL);
 
+	if (ll == IB_LINK_LAYER_ETHERNET && udata) {
+		int err;
+		struct mlx5_ib_create_ah_resp resp = {};
+		u32 min_resp_len = offsetof(typeof(resp), dmac) +
+				   sizeof(resp.dmac);
+
+		if (udata->outlen < min_resp_len)
+			return ERR_PTR(-EINVAL);
+
+		resp.response_length = min_resp_len;
+
+		err = ib_resolve_eth_dmac(pd->device, ah_attr);
+		if (err)
+			return ERR_PTR(err);
+
+		memcpy(resp.dmac, ah_attr->dmac, ETH_ALEN);
+		err = ib_copy_to_udata(udata, &resp, resp.response_length);
+		if (err)
+			return ERR_PTR(err);
+	}
+
 	ah = kzalloc(sizeof(*ah), GFP_ATOMIC);
 	if (!ah)
 		return ERR_PTR(-ENOMEM);

include/uapi/rdma/mlx5-abi.h

@@ -249,6 +249,12 @@ struct mlx5_ib_create_wq {
 	__u32   reserved;
 };
 
+struct mlx5_ib_create_ah_resp {
+	__u32	response_length;
+	__u8	dmac[ETH_ALEN];
+	__u8	reserved[6];
+};
+
 struct mlx5_ib_create_wq_resp {
 	__u32	response_length;
 	__u32	reserved;