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Date: Sun, 17 Dec 2023 18:40:11 -0800
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Subject: [RFC PATCH net-next v5 04/14] netdev: support binding dma-buf to netdevice
From: Mina Almasry <almasrymina@google.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Martin KaFai Lau <martin.lau@linux.dev>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-doc@vger.kernel.org, linux-alpha@vger.kernel.org, 
	linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, 
	sparclinux@vger.kernel.org, linux-trace-kernel@vger.kernel.org, 
	linux-arch@vger.kernel.org, bpf@vger.kernel.org, 
	linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, 
	dri-devel@lists.freedesktop.org
Cc: Mina Almasry <almasrymina@google.com>, "David S. Miller" <davem@davemloft.net>, 
	Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, 
	Jonathan Corbet <corbet@lwn.net>, Richard Henderson <richard.henderson@linaro.org>, 
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, 
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>, 
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, Helge Deller <deller@gmx.de>, 
	Jesper Dangaard Brouer <hawk@kernel.org>, Ilias Apalodimas <ilias.apalodimas@linaro.org>, 
	Steven Rostedt <rostedt@goodmis.org>, Masami Hiramatsu <mhiramat@kernel.org>, Arnd Bergmann <arnd@arndb.de>, 
	Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, 
	Andrii Nakryiko <andrii@kernel.org>, David Ahern <dsahern@kernel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>, Shuah Khan <shuah@kernel.org>, 
	Sumit Semwal <sumit.semwal@linaro.org>, 
	"=?UTF-8?q?Christian=20K=C3=B6nig?=" <christian.koenig@amd.com>, Pavel Begunkov <asml.silence@gmail.com>, 
	David Wei <dw@davidwei.uk>, Jason Gunthorpe <jgg@ziepe.ca>, Yunsheng Lin <linyunsheng@huawei.com>, 
	Shailend Chand <shailend@google.com>, Harshitha Ramamurthy <hramamurthy@google.com>, 
	Shakeel Butt <shakeelb@google.com>, Jeroen de Borst <jeroendb@google.com>, 
	Praveen Kaligineedi <pkaligineedi@google.com>, Willem de Bruijn <willemb@google.com>, 
	Kaiyuan Zhang <kaiyuanz@google.com>
Content-Type: text/plain; charset="UTF-8"

Add a netdev_dmabuf_binding struct which represents the
dma-buf-to-netdevice binding. The netlink API will bind the dma-buf to
rx queues on the netdevice. On the binding, the dma_buf_attach
& dma_buf_map_attachment will occur. The entries in the sg_table from
mapping will be inserted into a genpool to make it ready
for allocation.

The chunks in the genpool are owned by a dmabuf_chunk_owner struct which
holds the dma-buf offset of the base of the chunk and the dma_addr of
the chunk. Both are needed to use allocations that come from this chunk.

We create a new type that represents an allocation from the genpool:
net_iov. We setup the net_iov allocation size in the
genpool to PAGE_SIZE for simplicity: to match the PAGE_SIZE normally
allocated by the page pool and given to the drivers.

The user can unbind the dmabuf from the netdevice by closing the netlink
socket that established the binding. We do this so that the binding is
automatically unbound even if the userspace process crashes.

The binding and unbinding leaves an indicator in struct netdev_rx_queue
that the given queue is bound, but the binding doesn't take effect until
the driver actually reconfigures its queues, and re-initializes its page
pool.

The netdev_dmabuf_binding struct is refcounted, and releases its
resources only when all the refs are released.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>

---

RFC v5:
- Renamed page_pool_iov to net_iov, and moved that support to devmem.h
  or netmem.h.

v1:

- Introduce devmem.h instead of bloating netdevice.h (Jakub)
- ENOTSUPP -> EOPNOTSUPP (checkpatch.pl I think)
- Remove unneeded rcu protection for binding->list (rtnl protected)
- Removed extraneous err_binding_put: label.
- Removed dma_addr += len (Paolo).
- Don't override err on netdev_bind_dmabuf_to_queue failure.
- Rename devmem -> dmabuf (David).
- Add id to dmabuf binding (David/Stan).
- Fix missing xa_destroy bound_rq_list.
- Use queue api to reset bound RX queues (Jakub).
- Update netlink API for rx-queue type (tx/re) (Jakub).

RFC v3:
- Support multi rx-queue binding


netmem support

---
 include/net/devmem.h          | 115 ++++++++++++++
 include/net/netdev_rx_queue.h |   1 +
 include/net/netmem.h          |  10 ++
 net/core/dev.c                | 273 ++++++++++++++++++++++++++++++++++
 net/core/netdev-genl.c        | 121 ++++++++++++++-
 5 files changed, 518 insertions(+), 2 deletions(-)
 create mode 100644 include/net/devmem.h

diff --git a/include/net/devmem.h b/include/net/devmem.h
new file mode 100644
index 000000000000..85ccbbe84c65
--- /dev/null
+++ b/include/net/devmem.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Device memory TCP support
+ *
+ * Authors:	Mina Almasry <almasrymina@google.com>
+ *		Willem de Bruijn <willemb@google.com>
+ *		Kaiyuan Zhang <kaiyuanz@google.com>
+ *
+ */
+#ifndef _NET_DEVMEM_H
+#define _NET_DEVMEM_H
+
+struct netdev_dmabuf_binding {
+	struct dma_buf *dmabuf;
+	struct dma_buf_attachment *attachment;
+	struct sg_table *sgt;
+	struct net_device *dev;
+	struct gen_pool *chunk_pool;
+
+	/* The user holds a ref (via the netlink API) for as long as they want
+	 * the binding to remain alive. Each page pool using this binding holds
+	 * a ref to keep the binding alive. Each allocated net_iov holds a
+	 * ref.
+	 *
+	 * The binding undos itself and unmaps the underlying dmabuf once all
+	 * those refs are dropped and the binding is no longer desired or in
+	 * use.
+	 */
+	refcount_t ref;
+
+	/* The portid of the user that owns this binding. Used for netlink to
+	 * notify us of the user dropping the bind.
+	 */
+	u32 owner_nlportid;
+
+	/* The list of bindings currently active. Used for netlink to notify us
+	 * of the user dropping the bind.
+	 */
+	struct list_head list;
+
+	/* rxq's this binding is active on. */
+	struct xarray bound_rxq_list;
+
+	/* ID of this binding. Globally unique to all bindings currently
+	 * active.
+	 */
+	u32 id;
+};
+
+/* Owner of the dma-buf chunks inserted into the gen pool. Each scatterlist
+ * entry from the dmabuf is inserted into the genpool as a chunk, and needs
+ * this owner struct to keep track of some metadata necessary to create
+ * allocations from this chunk.
+ */
+struct dmabuf_genpool_chunk_owner {
+	/* Offset into the dma-buf where this chunk starts.  */
+	unsigned long base_virtual;
+
+	/* dma_addr of the start of the chunk.  */
+	dma_addr_t base_dma_addr;
+
+	/* Array of net_iovs for this chunk. */
+	struct net_iov *niovs;
+	size_t num_niovs;
+
+	struct netdev_dmabuf_binding *binding;
+};
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+void __netdev_dmabuf_binding_free(struct netdev_dmabuf_binding *binding);
+int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
+		       struct netdev_dmabuf_binding **out);
+void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding);
+int netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
+				struct netdev_dmabuf_binding *binding);
+#else
+static inline void
+__netdev_dmabuf_binding_free(struct netdev_dmabuf_binding *binding)
+{
+}
+
+static inline int netdev_bind_dmabuf(struct net_device *dev,
+				     unsigned int dmabuf_fd,
+				     struct netdev_dmabuf_binding **out)
+{
+	return -EOPNOTSUPP;
+}
+static inline void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding)
+{
+}
+
+static inline int
+netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
+			    struct netdev_dmabuf_binding *binding)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+static inline void
+netdev_dmabuf_binding_get(struct netdev_dmabuf_binding *binding)
+{
+	refcount_inc(&binding->ref);
+}
+
+static inline void
+netdev_dmabuf_binding_put(struct netdev_dmabuf_binding *binding)
+{
+	if (!refcount_dec_and_test(&binding->ref))
+		return;
+
+	__netdev_dmabuf_binding_free(binding);
+}
+
+#endif /* _NET_DEVMEM_H */
diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
index aa1716fb0e53..5dc35628633a 100644
--- a/include/net/netdev_rx_queue.h
+++ b/include/net/netdev_rx_queue.h
@@ -25,6 +25,7 @@ struct netdev_rx_queue {
 	 * Readers and writers must hold RTNL
 	 */
 	struct napi_struct		*napi;
+	struct netdev_dmabuf_binding *binding;
 } ____cacheline_aligned_in_smp;
 
 /*
diff --git a/include/net/netmem.h b/include/net/netmem.h
index b60b00216704..45eb42d9990b 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -8,6 +8,16 @@
 #ifndef _NET_NETMEM_H
 #define _NET_NETMEM_H
 
+#include <net/devmem.h>
+
+/* net_iov */
+
+struct net_iov {
+	struct dmabuf_genpool_chunk_owner *owner;
+};
+
+/* netmem */
+
 struct netmem {
 	union {
 		struct page page;
diff --git a/net/core/dev.c b/net/core/dev.c
index 0432b04cf9b0..2e474099267a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -153,6 +153,9 @@
 #include <linux/prandom.h>
 #include <linux/once_lite.h>
 #include <net/netdev_rx_queue.h>
+#include <linux/genalloc.h>
+#include <linux/dma-buf.h>
+#include <net/devmem.h>
 
 #include "dev.h"
 #include "net-sysfs.h"
@@ -2041,6 +2044,276 @@ static int call_netdevice_notifiers_mtu(unsigned long val,
 	return call_netdevice_notifiers_info(val, &info.info);
 }
 
+/* Device memory support */
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+static void netdev_dmabuf_free_chunk_owner(struct gen_pool *genpool,
+					   struct gen_pool_chunk *chunk,
+					   void *not_used)
+{
+	struct dmabuf_genpool_chunk_owner *owner = chunk->owner;
+
+	kvfree(owner->niovs);
+	kfree(owner);
+}
+
+void __netdev_dmabuf_binding_free(struct netdev_dmabuf_binding *binding)
+{
+	size_t size, avail;
+
+	gen_pool_for_each_chunk(binding->chunk_pool,
+				netdev_dmabuf_free_chunk_owner, NULL);
+
+	size = gen_pool_size(binding->chunk_pool);
+	avail = gen_pool_avail(binding->chunk_pool);
+
+	if (!WARN(size != avail, "can't destroy genpool. size=%lu, avail=%lu",
+		  size, avail))
+		gen_pool_destroy(binding->chunk_pool);
+
+	dma_buf_unmap_attachment(binding->attachment, binding->sgt,
+				 DMA_BIDIRECTIONAL);
+	dma_buf_detach(binding->dmabuf, binding->attachment);
+	dma_buf_put(binding->dmabuf);
+	xa_destroy(&binding->bound_rxq_list);
+	kfree(binding);
+}
+
+static int netdev_restart_rx_queue(struct net_device *dev, int rxq_idx)
+{
+	void *new_mem;
+	void *old_mem;
+	int err;
+
+	if (!dev || !dev->netdev_ops)
+		return -EINVAL;
+
+	if (!dev->netdev_ops->ndo_queue_stop ||
+	    !dev->netdev_ops->ndo_queue_mem_free ||
+	    !dev->netdev_ops->ndo_queue_mem_alloc ||
+	    !dev->netdev_ops->ndo_queue_start)
+		return -EOPNOTSUPP;
+
+	new_mem = dev->netdev_ops->ndo_queue_mem_alloc(dev, rxq_idx);
+	if (!new_mem)
+		return -ENOMEM;
+
+	err = dev->netdev_ops->ndo_queue_stop(dev, rxq_idx, &old_mem);
+	if (err)
+		goto err_free_new_mem;
+
+	err = dev->netdev_ops->ndo_queue_start(dev, rxq_idx, new_mem);
+	if (err)
+		goto err_start_queue;
+
+	dev->netdev_ops->ndo_queue_mem_free(dev, old_mem);
+
+	return 0;
+
+err_start_queue:
+	dev->netdev_ops->ndo_queue_start(dev, rxq_idx, old_mem);
+
+err_free_new_mem:
+	dev->netdev_ops->ndo_queue_mem_free(dev, new_mem);
+
+	return err;
+}
+
+/* Protected by rtnl_lock() */
+static DEFINE_XARRAY_FLAGS(netdev_dmabuf_bindings, XA_FLAGS_ALLOC1);
+
+void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding)
+{
+	struct netdev_rx_queue *rxq;
+	unsigned long xa_idx;
+	unsigned int rxq_idx;
+
+	if (!binding)
+		return;
+
+	if (binding->list.next)
+		list_del(&binding->list);
+
+	xa_for_each(&binding->bound_rxq_list, xa_idx, rxq) {
+		if (rxq->binding == binding) {
+			/* We hold the rtnl_lock while binding/unbinding
+			 * dma-buf, so we can't race with another thread that
+			 * is also modifying this value. However, the driver
+			 * may read this config while it's creating its
+			 * rx-queues. WRITE_ONCE() here to match the
+			 * READ_ONCE() in the driver.
+			 */
+			WRITE_ONCE(rxq->binding, NULL);
+
+			rxq_idx = get_netdev_rx_queue_index(rxq);
+
+			netdev_restart_rx_queue(binding->dev, rxq_idx);
+		}
+	}
+
+	xa_erase(&netdev_dmabuf_bindings, binding->id);
+
+	netdev_dmabuf_binding_put(binding);
+}
+
+int netdev_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
+				struct netdev_dmabuf_binding *binding)
+{
+	struct netdev_rx_queue *rxq;
+	u32 xa_idx;
+	int err;
+
+	rxq = __netif_get_rx_queue(dev, rxq_idx);
+
+	if (rxq->binding)
+		return -EEXIST;
+
+	err = xa_alloc(&binding->bound_rxq_list, &xa_idx, rxq, xa_limit_32b,
+		       GFP_KERNEL);
+	if (err)
+		return err;
+
+	/* We hold the rtnl_lock while binding/unbinding dma-buf, so we can't
+	 * race with another thread that is also modifying this value. However,
+	 * the driver may read this config while it's creating its * rx-queues.
+	 * WRITE_ONCE() here to match the READ_ONCE() in the driver.
+	 */
+	WRITE_ONCE(rxq->binding, binding);
+
+	err = netdev_restart_rx_queue(dev, rxq_idx);
+	if (err)
+		goto err_xa_erase;
+
+	return 0;
+
+err_xa_erase:
+	xa_erase(&binding->bound_rxq_list, xa_idx);
+	WRITE_ONCE(rxq->binding, NULL);
+
+	return err;
+}
+
+int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
+		       struct netdev_dmabuf_binding **out)
+{
+	struct netdev_dmabuf_binding *binding;
+	static u32 id_alloc_next;
+	struct scatterlist *sg;
+	struct dma_buf *dmabuf;
+	unsigned int sg_idx, i;
+	unsigned long virtual;
+	int err;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	dmabuf = dma_buf_get(dmabuf_fd);
+	if (IS_ERR_OR_NULL(dmabuf))
+		return -EBADFD;
+
+	binding = kzalloc_node(sizeof(*binding), GFP_KERNEL,
+			       dev_to_node(&dev->dev));
+	if (!binding) {
+		err = -ENOMEM;
+		goto err_put_dmabuf;
+	}
+	binding->dev = dev;
+
+	err = xa_alloc_cyclic(&netdev_dmabuf_bindings, &binding->id, binding,
+			      xa_limit_32b, &id_alloc_next, GFP_KERNEL);
+	if (err < 0)
+		goto err_free_binding;
+
+	xa_init_flags(&binding->bound_rxq_list, XA_FLAGS_ALLOC);
+
+	refcount_set(&binding->ref, 1);
+
+	binding->dmabuf = dmabuf;
+
+	binding->attachment = dma_buf_attach(binding->dmabuf, dev->dev.parent);
+	if (IS_ERR(binding->attachment)) {
+		err = PTR_ERR(binding->attachment);
+		goto err_free_id;
+	}
+
+	binding->sgt =
+		dma_buf_map_attachment(binding->attachment, DMA_BIDIRECTIONAL);
+	if (IS_ERR(binding->sgt)) {
+		err = PTR_ERR(binding->sgt);
+		goto err_detach;
+	}
+
+	/* For simplicity we expect to make PAGE_SIZE allocations, but the
+	 * binding can be much more flexible than that. We may be able to
+	 * allocate MTU sized chunks here. Leave that for future work...
+	 */
+	binding->chunk_pool =
+		gen_pool_create(PAGE_SHIFT, dev_to_node(&dev->dev));
+	if (!binding->chunk_pool) {
+		err = -ENOMEM;
+		goto err_unmap;
+	}
+
+	virtual = 0;
+	for_each_sgtable_dma_sg(binding->sgt, sg, sg_idx) {
+		dma_addr_t dma_addr = sg_dma_address(sg);
+		struct dmabuf_genpool_chunk_owner *owner;
+		size_t len = sg_dma_len(sg);
+		struct net_iov *niov;
+
+		owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
+				     dev_to_node(&dev->dev));
+		owner->base_virtual = virtual;
+		owner->base_dma_addr = dma_addr;
+		owner->num_niovs = len / PAGE_SIZE;
+		owner->binding = binding;
+
+		err = gen_pool_add_owner(binding->chunk_pool, dma_addr,
+					 dma_addr, len, dev_to_node(&dev->dev),
+					 owner);
+		if (err) {
+			err = -EINVAL;
+			goto err_free_chunks;
+		}
+
+		owner->niovs = kvmalloc_array(
+			owner->num_niovs, sizeof(*owner->niovs), GFP_KERNEL);
+		if (!owner->niovs) {
+			err = -ENOMEM;
+			goto err_free_chunks;
+		}
+
+		for (i = 0; i < owner->num_niovs; i++) {
+			niov = &owner->niovs[i];
+			niov->owner = owner;
+		}
+
+		virtual += len;
+	}
+
+	*out = binding;
+
+	return 0;
+
+err_free_chunks:
+	gen_pool_for_each_chunk(binding->chunk_pool,
+				netdev_dmabuf_free_chunk_owner, NULL);
+	gen_pool_destroy(binding->chunk_pool);
+err_unmap:
+	dma_buf_unmap_attachment(binding->attachment, binding->sgt,
+				 DMA_BIDIRECTIONAL);
+err_detach:
+	dma_buf_detach(dmabuf, binding->attachment);
+err_free_id:
+	xa_erase(&netdev_dmabuf_bindings, binding->id);
+err_free_binding:
+	kfree(binding);
+err_put_dmabuf:
+	dma_buf_put(dmabuf);
+	return err;
+}
+#endif
+
 #ifdef CONFIG_NET_INGRESS
 static DEFINE_STATIC_KEY_FALSE(ingress_needed_key);
 
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 0ed292d87ae0..8f0867ae5eeb 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -9,6 +9,7 @@
 #include <net/xdp_sock.h>
 #include <net/netdev_rx_queue.h>
 #include <net/busy_poll.h>
+#include <net/devmem.h>
 
 #include "netdev-genl-gen.h"
 #include "dev.h"
@@ -469,10 +470,93 @@ int netdev_nl_queue_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
-/* Stub */
+static LIST_HEAD(netdev_rbinding_list);
+
 int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return 0;
+	struct nlattr *tb[ARRAY_SIZE(netdev_queue_dmabuf_nl_policy)];
+	struct netdev_dmabuf_binding *out_binding;
+	u32 ifindex, dmabuf_fd, rxq_idx;
+	struct net_device *netdev;
+	struct sk_buff *rsp;
+	struct nlattr *attr;
+	int rem, err = 0;
+	void *hdr;
+
+	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||
+	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_BIND_DMABUF_DMABUF_FD) ||
+	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_BIND_DMABUF_QUEUES))
+		return -EINVAL;
+
+	ifindex = nla_get_u32(info->attrs[NETDEV_A_DEV_IFINDEX]);
+	dmabuf_fd = nla_get_u32(info->attrs[NETDEV_A_BIND_DMABUF_DMABUF_FD]);
+
+	rtnl_lock();
+
+	netdev = __dev_get_by_index(genl_info_net(info), ifindex);
+	if (!netdev) {
+		err = -ENODEV;
+		goto err_unlock;
+	}
+
+	err = netdev_bind_dmabuf(netdev, dmabuf_fd, &out_binding);
+	if (err)
+		goto err_unlock;
+
+	nla_for_each_attr(attr, genlmsg_data(info->genlhdr),
+			  genlmsg_len(info->genlhdr), rem) {
+		if (nla_type(attr) != NETDEV_A_BIND_DMABUF_QUEUES)
+			continue;
+
+		err = nla_parse_nested(
+			tb, ARRAY_SIZE(netdev_queue_dmabuf_nl_policy) - 1, attr,
+			netdev_queue_dmabuf_nl_policy, info->extack);
+
+		if (err < 0)
+			goto err_unbind;
+
+		rxq_idx = nla_get_u32(tb[NETDEV_A_QUEUE_DMABUF_IDX]);
+
+		if (rxq_idx >= netdev->num_rx_queues) {
+			err = -ERANGE;
+			goto err_unbind;
+		}
+
+		err = netdev_bind_dmabuf_to_queue(netdev, rxq_idx, out_binding);
+		if (err)
+			goto err_unbind;
+	}
+
+	out_binding->owner_nlportid = info->snd_portid;
+	list_add(&out_binding->list, &netdev_rbinding_list);
+
+	rsp = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!rsp) {
+		err = -ENOMEM;
+		goto err_unbind;
+	}
+
+	hdr = genlmsg_put(rsp, info->snd_portid, info->snd_seq,
+			  &netdev_nl_family, 0, info->genlhdr->cmd);
+	if (!hdr) {
+		err = -EMSGSIZE;
+		goto err_genlmsg_free;
+	}
+
+	nla_put_u32(rsp, NETDEV_A_BIND_DMABUF_DMABUF_ID, out_binding->id);
+	genlmsg_end(rsp, hdr);
+
+	rtnl_unlock();
+
+	return genlmsg_reply(rsp, info);
+
+err_genlmsg_free:
+	nlmsg_free(rsp);
+err_unbind:
+	netdev_unbind_dmabuf(out_binding);
+err_unlock:
+	rtnl_unlock();
+	return err;
 }
 
 static int netdev_genl_netdevice_event(struct notifier_block *nb,
@@ -495,10 +579,37 @@ static int netdev_genl_netdevice_event(struct notifier_block *nb,
 	return NOTIFY_OK;
 }
 
+static int netdev_netlink_notify(struct notifier_block *nb, unsigned long state,
+				 void *_notify)
+{
+	struct netlink_notify *notify = _notify;
+	struct netdev_dmabuf_binding *rbinding;
+
+	if (state != NETLINK_URELEASE || notify->protocol != NETLINK_GENERIC)
+		return NOTIFY_DONE;
+
+	rtnl_lock();
+
+	list_for_each_entry(rbinding, &netdev_rbinding_list, list) {
+		if (rbinding->owner_nlportid == notify->portid) {
+			netdev_unbind_dmabuf(rbinding);
+			break;
+		}
+	}
+
+	rtnl_unlock();
+
+	return NOTIFY_OK;
+}
+
 static struct notifier_block netdev_genl_nb = {
 	.notifier_call	= netdev_genl_netdevice_event,
 };
 
+static struct notifier_block netdev_netlink_notifier = {
+	.notifier_call = netdev_netlink_notify,
+};
+
 static int __init netdev_genl_init(void)
 {
 	int err;
@@ -511,8 +622,14 @@ static int __init netdev_genl_init(void)
 	if (err)
 		goto err_unreg_ntf;
 
+	err = netlink_register_notifier(&netdev_netlink_notifier);
+	if (err)
+		goto err_unreg_family;
+
 	return 0;
 
+err_unreg_family:
+	genl_unregister_family(&netdev_nl_family);
 err_unreg_ntf:
 	unregister_netdevice_notifier(&netdev_genl_nb);
 	return err;
-- 
2.43.0.472.g3155946c3a-goog