RDMA/mlx5: Use UMEM attribute for QP doorbell record

Add an optional mlx5 driver-namespace UMEM attribute on QP
create so userspace can supply the doorbell record umem
explicitly, symmetric to the CQ side. Resolve it inside
mlx5_ib_db_map_user() and use it as a private DBR page when
present; otherwise take the existing UHW share-or-pin path
that preserves per-page DBR sharing across CQ/QP/SRQ in the
same process.

Add mlx5's first UVERBS_OBJECT_QP UAPI definition chain to
attach the new attr.

Link: https://patch.msgid.link/r/20260529134312.2836341-17-jiri@resnulli.us
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

4 files changed, 24 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 419489bd2199..12bfefc91b02 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -4456,6 +4456,7 @@ static const struct uapi_definition mlx5_ib_defs[] = {
 	UAPI_DEF_CHAIN(mlx5_ib_std_types_defs),
 	UAPI_DEF_CHAIN(mlx5_ib_dm_defs),
 	UAPI_DEF_CHAIN(mlx5_ib_create_cq_defs),
+	UAPI_DEF_CHAIN(mlx5_ib_create_qp_defs),
 
 	UAPI_DEF_CHAIN_OBJ_TREE(UVERBS_OBJECT_DEVICE, &mlx5_ib_query_context),
 	UAPI_DEF_CHAIN_OBJ_TREE(UVERBS_OBJECT_MR, &mlx5_ib_reg_dmabuf_mr),
diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index 078f281bcdac..1f03c05b0cbd 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -1511,6 +1511,7 @@ extern const struct uapi_definition mlx5_ib_flow_defs[];
 extern const struct uapi_definition mlx5_ib_qos_defs[];
 extern const struct uapi_definition mlx5_ib_std_types_defs[];
 extern const struct uapi_definition mlx5_ib_create_cq_defs[];
+extern const struct uapi_definition mlx5_ib_create_qp_defs[];
 
 static inline int is_qp1(enum ib_qp_type qp_type)
 {
diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
index 58997714df70..e8d34d54b435 100644
--- a/drivers/infiniband/hw/mlx5/qp.c
+++ b/drivers/infiniband/hw/mlx5/qp.c
@@ -44,6 +44,9 @@
 #include "qp.h"
 #include "wr.h"
 
+#define UVERBS_MODULE_NAME mlx5_ib
+#include <rdma/uverbs_named_ioctl.h>
+
 enum {
 	MLX5_IB_ACK_REQ_FREQ	= 8,
 };
@@ -1053,7 +1056,9 @@ static int _create_user_qp(struct mlx5_ib_dev *dev, struct ib_pd *pd,
 		resp->bfreg_index = MLX5_IB_INVALID_BFREG;
 	qp->bfregn = bfregn;
 
-	err = mlx5_ib_db_map_user(context, NULL, 0, ucmd->db_addr, &qp->db);
+	err = mlx5_ib_db_map_user(context, attrs,
+				  MLX5_IB_ATTR_CREATE_QP_DBR_BUF_UMEM,
+				  ucmd->db_addr, &qp->db);
 	if (err) {
 		mlx5_ib_dbg(dev, "map failed\n");
 		goto err_free;
@@ -5877,3 +5882,15 @@ void mlx5_ib_qp_event_cleanup(void)
 {
 	destroy_workqueue(mlx5_ib_qp_event_wq);
 }
+
+ADD_UVERBS_ATTRIBUTES_SIMPLE(
+	mlx5_ib_qp_create,
+	UVERBS_OBJECT_QP,
+	UVERBS_METHOD_QP_CREATE,
+	UVERBS_ATTR_UMEM(MLX5_IB_ATTR_CREATE_QP_DBR_BUF_UMEM,
+			 UA_OPTIONAL));
+
+const struct uapi_definition mlx5_ib_create_qp_defs[] = {
+	UAPI_DEF_CHAIN_OBJ_TREE(UVERBS_OBJECT_QP, &mlx5_ib_qp_create),
+	{},
+};
diff --git a/include/uapi/rdma/mlx5_user_ioctl_cmds.h b/include/uapi/rdma/mlx5_user_ioctl_cmds.h
index b63e75034cda..ddb898afd813 100644
--- a/include/uapi/rdma/mlx5_user_ioctl_cmds.h
+++ b/include/uapi/rdma/mlx5_user_ioctl_cmds.h
@@ -277,6 +277,10 @@ enum mlx5_ib_create_cq_attrs {
 	MLX5_IB_ATTR_CREATE_CQ_DBR_BUF_UMEM,
 };
 
+enum mlx5_ib_create_qp_attrs {
+	MLX5_IB_ATTR_CREATE_QP_DBR_BUF_UMEM = UVERBS_ID_DRIVER_NS_WITH_UHW,
+};
+
 enum mlx5_ib_reg_dmabuf_mr_attrs {
 	MLX5_IB_ATTR_REG_DMABUF_MR_ACCESS_FLAGS = (1U << UVERBS_ID_NS_SHIFT),
 };