From: Maher Sanalla <msanalla@nvidia.com>

Introduce MLX5_IB_METHOD_VAR_OBJ_QUERY to enable cross-process sharing
of VAR objects. This method allows a process that has imported the uverbs
fd via ibv_import_device() to query an existing VAR handle and obtain
the mmap parameters needed to map the VAR region into its address space.

This follows the same pattern as UVERBS_METHOD_QUERY_MR, allowing
userspace to implement mlx5dv_import_var() analogous to ibv_import_mr().

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/infiniband/hw/mlx5/main.c        | 47 +++++++++++++++++++++++++++++++-
 include/uapi/rdma/mlx5_user_ioctl_cmds.h |  8 ++++++
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 77cd11c6cca9..a75769f55d31 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -4263,6 +4263,34 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_VAR_OBJ_ALLOC)(
 	return err;
 }
 
+static int UVERBS_HANDLER(MLX5_IB_METHOD_VAR_OBJ_QUERY)(
+	struct uverbs_attr_bundle *attrs)
+{
+	struct mlx5_user_mmap_entry *entry =
+		uverbs_attr_get_obj(attrs, MLX5_IB_ATTR_VAR_OBJ_QUERY_HANDLE);
+	u64 mmap_offset;
+	u32 length;
+	int err;
+
+	mmap_offset = mlx5_entry_to_mmap_offset(entry);
+	if (check_mul_overflow(entry->rdma_entry.npages, (u32)PAGE_SIZE, &length))
+		return -EOVERFLOW;
+
+	err = uverbs_copy_to(attrs, MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_OFFSET,
+			     &mmap_offset, sizeof(mmap_offset));
+	if (err)
+		return err;
+
+	err = uverbs_copy_to(attrs, MLX5_IB_ATTR_VAR_OBJ_QUERY_PAGE_ID,
+			     &entry->page_idx, sizeof(entry->page_idx));
+	if (err)
+		return err;
+
+	err = uverbs_copy_to(attrs, MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_LENGTH,
+			     &length, sizeof(length));
+	return err;
+}
+
 DECLARE_UVERBS_NAMED_METHOD(
 	MLX5_IB_METHOD_VAR_OBJ_ALLOC,
 	UVERBS_ATTR_IDR(MLX5_IB_ATTR_VAR_OBJ_ALLOC_HANDLE,
@@ -4289,10 +4317,27 @@ DECLARE_UVERBS_NAMED_METHOD_DESTROY(
 			UVERBS_ACCESS_DESTROY,
 			UA_MANDATORY));
 
+DECLARE_UVERBS_NAMED_METHOD(
+	MLX5_IB_METHOD_VAR_OBJ_QUERY,
+	UVERBS_ATTR_IDR(MLX5_IB_ATTR_VAR_OBJ_QUERY_HANDLE,
+			MLX5_IB_OBJECT_VAR,
+			UVERBS_ACCESS_READ,
+			UA_MANDATORY),
+	UVERBS_ATTR_PTR_OUT(MLX5_IB_ATTR_VAR_OBJ_QUERY_PAGE_ID,
+			    UVERBS_ATTR_TYPE(u32),
+			    UA_MANDATORY),
+	UVERBS_ATTR_PTR_OUT(MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_LENGTH,
+			    UVERBS_ATTR_TYPE(u32),
+			    UA_MANDATORY),
+	UVERBS_ATTR_PTR_OUT(MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_OFFSET,
+			    UVERBS_ATTR_TYPE(u64),
+			    UA_MANDATORY));
+
 DECLARE_UVERBS_NAMED_OBJECT(MLX5_IB_OBJECT_VAR,
 			    UVERBS_TYPE_ALLOC_IDR(mmap_obj_cleanup),
 			    &UVERBS_METHOD(MLX5_IB_METHOD_VAR_OBJ_ALLOC),
-			    &UVERBS_METHOD(MLX5_IB_METHOD_VAR_OBJ_DESTROY));
+			    &UVERBS_METHOD(MLX5_IB_METHOD_VAR_OBJ_DESTROY),
+			    &UVERBS_METHOD(MLX5_IB_METHOD_VAR_OBJ_QUERY));
 
 static bool var_is_supported(struct ib_device *device)
 {
diff --git a/include/uapi/rdma/mlx5_user_ioctl_cmds.h b/include/uapi/rdma/mlx5_user_ioctl_cmds.h
index 01a2a050e468..7db03b3fdae6 100644
--- a/include/uapi/rdma/mlx5_user_ioctl_cmds.h
+++ b/include/uapi/rdma/mlx5_user_ioctl_cmds.h
@@ -146,9 +146,17 @@ enum mlx5_ib_var_obj_destroy_attrs {
 	MLX5_IB_ATTR_VAR_OBJ_DESTROY_HANDLE = (1U << UVERBS_ID_NS_SHIFT),
 };
 
+enum mlx5_ib_var_obj_query_attrs {
+	MLX5_IB_ATTR_VAR_OBJ_QUERY_HANDLE = (1U << UVERBS_ID_NS_SHIFT),
+	MLX5_IB_ATTR_VAR_OBJ_QUERY_PAGE_ID,
+	MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_OFFSET,
+	MLX5_IB_ATTR_VAR_OBJ_QUERY_MMAP_LENGTH,
+};
+
 enum mlx5_ib_var_obj_methods {
 	MLX5_IB_METHOD_VAR_OBJ_ALLOC = (1U << UVERBS_ID_NS_SHIFT),
 	MLX5_IB_METHOD_VAR_OBJ_DESTROY,
+	MLX5_IB_METHOD_VAR_OBJ_QUERY,
 };
 
 enum mlx5_ib_uar_alloc_attrs {

-- 
2.53.0