Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice

[David Wei <dw@davidwei.uk>]

On 2023-11-05 18:44, Mina Almasry wrote:
> 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:
> page_pool_iov. We setup the page_pool_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 v3:
> - Support multi rx-queue binding
> 
> ---
>  include/linux/netdevice.h     |  80 ++++++++++++++
>  include/net/netdev_rx_queue.h |   1 +
>  include/net/page_pool/types.h |  27 +++++
>  net/core/dev.c                | 203 ++++++++++++++++++++++++++++++++++
>  net/core/netdev-genl.c        | 116 ++++++++++++++++++-
>  5 files changed, 425 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index b8bf669212cc..eeeda849115c 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -52,6 +52,8 @@
>  #include <net/net_trackers.h>
>  #include <net/net_debug.h>
>  #include <net/dropreason-core.h>
> +#include <linux/xarray.h>
> +#include <linux/refcount.h>
>  
>  struct netpoll_info;
>  struct device;
> @@ -808,6 +810,84 @@ bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index, u32 flow_id,
>  #endif
>  #endif /* CONFIG_RPS */
>  
> +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 page_pool_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;
> +};
> +
> +#ifdef CONFIG_DMA_SHARED_BUFFER
> +void __netdev_devmem_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_devmem_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_devmem_binding_get(struct netdev_dmabuf_binding *binding)
> +{
> +	refcount_inc(&binding->ref);
> +}
> +
> +static inline void
> +netdev_devmem_binding_put(struct netdev_dmabuf_binding *binding)
> +{
> +	if (!refcount_dec_and_test(&binding->ref))
> +		return;
> +
> +	__netdev_devmem_binding_free(binding);
> +}
> +
>  /* XPS map type and offset of the xps map within net_device->xps_maps[]. */
>  enum xps_map_type {
>  	XPS_CPUS = 0,
> diff --git a/include/net/netdev_rx_queue.h b/include/net/netdev_rx_queue.h
> index cdcafb30d437..1bfcf60a145d 100644
> --- a/include/net/netdev_rx_queue.h
> +++ b/include/net/netdev_rx_queue.h
> @@ -21,6 +21,7 @@ struct netdev_rx_queue {
>  #ifdef CONFIG_XDP_SOCKETS
>  	struct xsk_buff_pool            *pool;
>  #endif
> +	struct netdev_dmabuf_binding *binding;

@Pavel - They are using struct netdev_rx_queue to hold the binding,
which is an object that holds the state and is mapped 1:1 to an rxq.
This object is similar to our "interface queue". I wonder if we should
re-visit using this generic struct, instead of driver specific structs
e.g. bnxt_rx_ring_info?

>  } ____cacheline_aligned_in_smp;
>  
>  /*
> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> index d4bea053bb7e..64386325d965 100644
> --- a/include/net/page_pool/types.h
> +++ b/include/net/page_pool/types.h
> @@ -133,6 +133,33 @@ struct pp_memory_provider_ops {
>  	bool (*release_page)(struct page_pool *pool, struct page *page);
>  };
>  
> +/* page_pool_iov support */
> +
> +/* 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 page_pool_iovs for this chunk. */
> +	struct page_pool_iov *ppiovs;
> +	size_t num_ppiovs;
> +
> +	struct netdev_dmabuf_binding *binding;
> +};
> +
> +struct page_pool_iov {
> +	struct dmabuf_genpool_chunk_owner *owner;
> +
> +	refcount_t refcount;
> +};
> +
>  struct page_pool {
>  	struct page_pool_params p;
>  
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a37a932a3e14..c8c3709d42c8 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/page_pool/types.h>
>  
>  #include "dev.h"
>  #include "net-sysfs.h"
> @@ -2040,6 +2043,206 @@ 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_devmem_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->ppiovs);
> +	kfree(owner);
> +}
> +
> +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding)
> +{
> +	size_t size, avail;
> +
> +	gen_pool_for_each_chunk(binding->chunk_pool,
> +				netdev_devmem_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);
> +	kfree(binding);
> +}
> +
> +void netdev_unbind_dmabuf(struct netdev_dmabuf_binding *binding)
> +{
> +	struct netdev_rx_queue *rxq;
> +	unsigned long xa_idx;
> +
> +	if (!binding)
> +		return;
> +
> +	list_del_rcu(&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);
> +
> +	netdev_devmem_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);
> +
> +	return 0;
> +}
> +
> +int netdev_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,
> +		       struct netdev_dmabuf_binding **out)

I'm not entirely familiar with the Netlink API. Mina, do you know if we
can call into netdev_bind_dmabuf or netdev_nl_bind_rx_doit directly,
without needing to call send/recv on a Netlink socket? We likely want
io_uring to do the registration of a dmabuf fd and keep ownership over
it.

> +{
> +	struct netdev_dmabuf_binding *binding;
> +	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;
> +	}
> +
> +	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_binding;
> +	}
> +
> +	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 page_pool_iov *ppiov;
> +
> +		owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
> +				     dev_to_node(&dev->dev));
> +		owner->base_virtual = virtual;
> +		owner->base_dma_addr = dma_addr;
> +		owner->num_ppiovs = 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->ppiovs = kvmalloc_array(owner->num_ppiovs,
> +					       sizeof(*owner->ppiovs),
> +					       GFP_KERNEL);
> +		if (!owner->ppiovs) {
> +			err = -ENOMEM;
> +			goto err_free_chunks;
> +		}
> +
> +		for (i = 0; i < owner->num_ppiovs; i++) {
> +			ppiov = &owner->ppiovs[i];
> +			ppiov->owner = owner;
> +			refcount_set(&ppiov->refcount, 1);
> +		}
> +
> +		dma_addr += len;
> +		virtual += len;
> +	}
> +
> +	*out = binding;
> +
> +	return 0;
> +
> +err_free_chunks:
> +	gen_pool_for_each_chunk(binding->chunk_pool,
> +				netdev_devmem_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_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 59d3d512d9cc..2c2a62593217 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -129,10 +129,89 @@ int netdev_nl_dev_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 netdev_dmabuf_binding *out_binding;
> +	u32 ifindex, dmabuf_fd, rxq_idx;
> +	struct net_device *netdev;
> +	struct sk_buff *rsp;
> +	int rem, err = 0;
> +	void *hdr;
> +	struct nlattr *attr;
> +
> +	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) {
> +		switch (nla_type(attr)) {
> +		case NETDEV_A_BIND_DMABUF_QUEUES:
> +			rxq_idx = nla_get_u32(attr);
> +
> +			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;
> +
> +			break;
> +		default:
> +			break;
> +		}
> +	}
> +
> +	out_binding->owner_nlportid = info->snd_portid;
> +	list_add_rcu(&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;
> +	}
> +
> +	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,
> @@ -155,10 +234,37 @@ 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;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry_rcu(rbinding, &netdev_rbinding_list, list) {
> +		if (rbinding->owner_nlportid == notify->portid) {
> +			netdev_unbind_dmabuf(rbinding);
> +			break;
> +		}
> +	}
> +
> +	rcu_read_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,
> +};

Is this mechamism what cleans up TCP devmem in case userspace crashes
and the associated Netlink socket is closed?

> +
>  static int __init netdev_genl_init(void)
>  {
>  	int err;
> @@ -171,8 +277,14 @@ 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;