RDMA/uverbs: Add DMABUF object type and operations

Expose DMABUF functionality to userspace through the uverbs interface,
enabling InfiniBand/RDMA devices to export PCI based memory regions
(e.g. device memory) as DMABUF file descriptors. This allows
zero-copy sharing of RDMA memory with other subsystems that support the
dma-buf framework.

A new UVERBS_OBJECT_DMABUF object type and allocation method were
introduced.

During allocation, uverbs invokes the driver to supply the
rdma_user_mmap_entry associated with the given page offset (pgoff).

Based on the returned rdma_user_mmap_entry, uverbs requests the driver
to provide the corresponding physical-memory details as well as the
driver’s PCI provider information.

Using this information, dma_buf_export() is called; if it succeeds,
uobj->object is set to the underlying file pointer returned by the
dma-buf framework.

The file descriptor number follows the standard uverbs allocation flow,
but the file pointer comes from the dma-buf subsystem, including its own
fops and private data.

When an mmap entry is removed, uverbs iterates over its associated
DMABUFs, marks them as revoked, and calls dma_buf_move_notify() so that
their importers are notified.

The same procedure applies during the disassociate flow; final cleanup
occurs when the application closes the file.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
Link: https://patch.msgid.link/20260201-dmabuf-export-v3-2-da238b614fe3@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

3 files changed, 20 insertions, 0 deletions

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 8bd020da7745..3f3827e1c711 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -44,6 +44,7 @@
 #include <uapi/rdma/rdma_user_ioctl.h>
 #include <uapi/rdma/ib_user_ioctl_verbs.h>
 #include <linux/pci-tph.h>
+#include <linux/dma-buf.h>
 
 #define IB_FW_VERSION_NAME_MAX	ETHTOOL_FWVERS_LEN
 
@@ -2364,6 +2365,9 @@ struct rdma_user_mmap_entry {
 	unsigned long start_pgoff;
 	size_t npages;
 	bool driver_removed;
+	/* protects access to dmabufs */
+	struct mutex dmabufs_lock;
+	struct list_head dmabufs;
 };
 
 /* Return the offset (in bytes) the user should pass to libc's mmap() */
@@ -2501,6 +2505,11 @@ struct ib_device_ops {
 	 * Therefore needs to be implemented by the driver in mmap_free.
 	 */
 	void (*mmap_free)(struct rdma_user_mmap_entry *entry);
+	int (*mmap_get_pfns)(struct rdma_user_mmap_entry *entry,
+			     struct phys_vec *phys_vec,
+			     struct p2pdma_provider **provider);
+	struct rdma_user_mmap_entry *(*pgoff_to_mmap_entry)(struct ib_ucontext *ucontext,
+							    off_t pg_off);
 	void (*disassociate_ucontext)(struct ib_ucontext *ibcontext);
 	int (*alloc_pd)(struct ib_pd *pd, struct ib_udata *udata);
 	int (*dealloc_pd)(struct ib_pd *pd, struct ib_udata *udata);
diff --git a/include/rdma/uverbs_types.h b/include/rdma/uverbs_types.h
index 26ba919ac245..6a253b7dc5ea 100644
--- a/include/rdma/uverbs_types.h
+++ b/include/rdma/uverbs_types.h
@@ -186,6 +186,7 @@ struct ib_uverbs_file {
 extern const struct uverbs_obj_type_class uverbs_idr_class;
 extern const struct uverbs_obj_type_class uverbs_fd_class;
 int uverbs_uobject_fd_release(struct inode *inode, struct file *filp);
+int uverbs_uobject_release(struct ib_uobject *uobj);
 
 #define UVERBS_BUILD_BUG_ON(cond) (sizeof(char[1 - 2 * !!(cond)]) -	\
 				   sizeof(char))
diff --git a/include/uapi/rdma/ib_user_ioctl_cmds.h b/include/uapi/rdma/ib_user_ioctl_cmds.h
index 35da4026f452..72041c1b0ea5 100644
--- a/include/uapi/rdma/ib_user_ioctl_cmds.h
+++ b/include/uapi/rdma/ib_user_ioctl_cmds.h
@@ -56,6 +56,7 @@ enum uverbs_default_objects {
 	UVERBS_OBJECT_COUNTERS,
 	UVERBS_OBJECT_ASYNC_EVENT,
 	UVERBS_OBJECT_DMAH,
+	UVERBS_OBJECT_DMABUF,
 };
 
 enum {
@@ -263,6 +264,15 @@ enum uverbs_methods_dmah {
 	UVERBS_METHOD_DMAH_FREE,
 };
 
+enum uverbs_attrs_alloc_dmabuf_cmd_attr_ids {
+	UVERBS_ATTR_ALLOC_DMABUF_HANDLE,
+	UVERBS_ATTR_ALLOC_DMABUF_PGOFF,
+};
+
+enum uverbs_methods_dmabuf {
+	UVERBS_METHOD_DMABUF_ALLOC,
+};
+
 enum uverbs_attrs_reg_dm_mr_cmd_attr_ids {
 	UVERBS_ATTR_REG_DM_MR_HANDLE,
 	UVERBS_ATTR_REG_DM_MR_OFFSET,