Re: [PATCH RFC net-next v1 5/5] net: devmem: Implement TX path

On 12/21, Mina Almasry wrote:

Augment dmabuf binding to be able to handle TX. Additional to all the RX binding, we also create tx_vec and tx_iter needed for the TX path.

Provide API for sendmsg to be able to send dmabufs bound to this device:

• Provide a new dmabuf_tx_cmsg which includes the dmabuf to send from, and the offset into the dmabuf to send from.
• MSG_ZEROCOPY with SCM_DEVMEM_DMABUF cmsg indicates send from dma-buf.

Devmem is uncopyable, so piggyback off the existing MSG_ZEROCOPY implementation, while disabling instances where MSG_ZEROCOPY falls back to copying.

We additionally look up the dmabuf to send from by id, then pipe the binding down to the new zerocopy_fill_skb_from_devmem which fills a TX skb with net_iov netmems instead of the traditional page netmems.

We also special case skb_frag_dma_map to return the dma-address of these dmabuf net_iovs instead of attempting to map pages.

Based on work by Stanislav Fomichev sdf@fomichev.me. A lot of the meat of the implementation came from devmem TCP RFC v1[1], which included the TX path, but Stan did all the rebasing on top of netmem/net_iov.

Cc: Stanislav Fomichev sdf@fomichev.me Signed-off-by: Kaiyuan Zhang kaiyuanz@google.com Signed-off-by: Mina Almasry almasrymina@google.com

---

include/linux/skbuff.h | 13 +++- include/net/sock.h | 2 + include/uapi/linux/uio.h | 5 ++ net/core/datagram.c | 40 ++++++++++- net/core/devmem.c | 91 +++++++++++++++++++++++-- net/core/devmem.h | 40 +++++++++-- net/core/netdev-genl.c | 65 +++++++++++++++++- net/core/skbuff.c | 8 ++- net/core/sock.c | 9 +++ net/ipv4/tcp.c | 36 +++++++--- net/vmw_vsock/virtio_transport_common.c | 4 +- 11 files changed, 281 insertions(+), 32 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index bb2b751d274a..e90dc0c4d542 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1711,9 +1711,10 @@ struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size, void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref); +struct net_devmem_dmabuf_binding; int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk, struct sk_buff *skb, struct iov_iter *from,

• 	    size_t length);
  

• 	    size_t length, bool is_devmem);
  

int zerocopy_fill_skb_from_iter(struct sk_buff *skb, struct iov_iter *from, size_t length); @@ -1721,12 +1722,14 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb, static inline int skb_zerocopy_iter_dgram(struct sk_buff *skb, struct msghdr *msg, int len) {

• return __zerocopy_sg_from_iter(msg, skb->sk, skb, &msg->msg_iter, len);

• return __zerocopy_sg_from_iter(msg, skb->sk, skb, &msg->msg_iter, len,

• 		       false);
  

} int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, struct msghdr *msg, int len,

• 	     struct ubuf_info *uarg);
  

• 	     struct ubuf_info *uarg,
  

• 	     struct net_devmem_dmabuf_binding *binding);
  

/* Internal */ #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB))) @@ -3697,6 +3700,10 @@ static inline dma_addr_t __skb_frag_dma_map(struct device *dev, size_t offset, size_t size, enum dma_data_direction dir) {

• if (skb_frag_is_net_iov(frag)) {

• return netmem_to_net_iov(frag->netmem)->dma_addr + offset +
  

•        frag->offset;
  

• } return dma_map_page(dev, skb_frag_page(frag), skb_frag_off(frag) + offset, size, dir);

} diff --git a/include/net/sock.h b/include/net/sock.h index d4bdd3286e03..75bd580fe9c6 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1816,6 +1816,8 @@ struct sockcm_cookie { u32 tsflags; u32 ts_opt_id; u32 priority;

• u32 dmabuf_id;
• u64 dmabuf_offset;

}; static inline void sockcm_init(struct sockcm_cookie *sockc, diff --git a/include/uapi/linux/uio.h b/include/uapi/linux/uio.h index 649739e0c404..41490cde95ad 100644 --- a/include/uapi/linux/uio.h +++ b/include/uapi/linux/uio.h @@ -38,6 +38,11 @@ struct dmabuf_token { __u32 token_count; }; +struct dmabuf_tx_cmsg {

• __u32 dmabuf_id;
• __u64 dmabuf_offset;

+};

/*

• UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)

*/ diff --git a/net/core/datagram.c b/net/core/datagram.c index f0693707aece..3b09995db894 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -63,6 +63,8 @@ #include <net/busy_poll.h> #include <crypto/hash.h> +#include "devmem.h"

/*

• Is a socket 'connection oriented' ?

*/ @@ -692,9 +694,41 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb, return 0; } +static int zerocopy_fill_skb_from_devmem(struct sk_buff *skb,

• 			 struct msghdr *msg,
  

• 			 struct iov_iter *from, int length)
  

+{

• int i = skb_shinfo(skb)->nr_frags;
• int orig_length = length;
• netmem_ref netmem;
• size_t size;
• while (length && iov_iter_count(from)) {

• if (i == MAX_SKB_FRAGS)
  

• 	return -EMSGSIZE;
  

• size = min_t(size_t, iter_iov_len(from), length);
  

• if (!size)
  

• 	return -EFAULT;
  

• netmem = net_iov_to_netmem(iter_iov(from)->iov_base);
  

• get_netmem(netmem);
  

• skb_add_rx_frag_netmem(skb, i, netmem, from->iov_offset, size,
  

• 		       PAGE_SIZE);
  

• iov_iter_advance(from, size);
  

• length -= size;
  

• i++;
  

• }
• iov_iter_advance(&msg->msg_iter, orig_length);
• return 0;

+}

int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk, struct sk_buff *skb, struct iov_iter *from,

• 	    size_t length)
  

• 	    size_t length, bool is_devmem)
  

{ unsigned long orig_size = skb->truesize; unsigned long truesize; @@ -702,6 +736,8 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk, if (msg && msg->msg_ubuf && msg->sg_from_iter) ret = msg->sg_from_iter(skb, from, length);

• else if (unlikely(is_devmem))

• ret = zerocopy_fill_skb_from_devmem(skb, msg, from, length);
  

  else ret = zerocopy_fill_skb_from_iter(skb, from, length);

@@ -735,7 +771,7 @@ int zerocopy_sg_from_iter(struct sk_buff *skb, struct iov_iter *from) if (skb_copy_datagram_from_iter(skb, 0, from, copy)) return -EFAULT;

• return __zerocopy_sg_from_iter(NULL, NULL, skb, from, ~0U);

• return __zerocopy_sg_from_iter(NULL, NULL, skb, from, ~0U, NULL);

} EXPORT_SYMBOL(zerocopy_sg_from_iter); diff --git a/net/core/devmem.c b/net/core/devmem.c index f7e06a8cba01..81f1b715cfa6 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -15,6 +15,7 @@ #include <net/netdev_queues.h> #include <net/netdev_rx_queue.h> #include <net/page_pool/helpers.h> +#include <net/sock.h> #include <trace/events/page_pool.h> #include "devmem.h" @@ -63,8 +64,10 @@ void __net_devmem_dmabuf_binding_free(struct net_devmem_dmabuf_binding *binding) dma_buf_detach(binding->dmabuf, binding->attachment); dma_buf_put(binding->dmabuf); xa_destroy(&binding->bound_rxqs);

• kfree(binding->tx_vec); kfree(binding);

} +EXPORT_SYMBOL(__net_devmem_dmabuf_binding_free); struct net_iov * net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding) @@ -109,6 +112,13 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) unsigned long xa_idx; unsigned int rxq_idx;

• xa_erase(&net_devmem_dmabuf_bindings, binding->id);
• /* Ensure no tx net_devmem_lookup_dmabuf() are in flight after the

• * erase.
  

• */
  

• synchronize_net();
• if (binding->list.next) list_del(&binding->list);

@@ -122,8 +132,6 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) WARN_ON(netdev_rx_queue_restart(binding->dev, rxq_idx)); }

• xa_erase(&net_devmem_dmabuf_bindings, binding->id);
• net_devmem_dmabuf_binding_put(binding);

} @@ -174,8 +182,9 @@ int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx, } struct net_devmem_dmabuf_binding * -net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,

•        struct netlink_ext_ack *extack)
  

+net_devmem_bind_dmabuf(struct net_device *dev,

•        enum dma_data_direction direction,
  

•        unsigned int dmabuf_fd, struct netlink_ext_ack *extack)
  

{ struct net_devmem_dmabuf_binding *binding; static u32 id_alloc_next; @@ -183,6 +192,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, struct dma_buf *dmabuf; unsigned int sg_idx, i; unsigned long virtual;

• struct iovec *iov; int err;

dmabuf = dma_buf_get(dmabuf_fd); @@ -218,13 +228,19 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, } binding->sgt = dma_buf_map_attachment_unlocked(binding->attachment,

• 				       DMA_FROM_DEVICE);
  

• 				       direction);
  

  if (IS_ERR(binding->sgt)) { err = PTR_ERR(binding->sgt); NL_SET_ERR_MSG(extack, "Failed to map dmabuf attachment"); goto err_detach; }

• if (!binding->sgt || binding->sgt->nents == 0) {

• err = -EINVAL;
  

• NL_SET_ERR_MSG(extack, "Empty dmabuf attachment");
  

• 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...

@@ -236,6 +252,19 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, goto err_unmap; }

• if (direction == DMA_TO_DEVICE) {

• virtual = 0;
  

• for_each_sgtable_dma_sg(binding->sgt, sg, sg_idx)
  

• 	virtual += sg_dma_len(sg);
  

• binding->tx_vec = kcalloc(virtual / PAGE_SIZE + 1,
  

• 			  sizeof(struct iovec), GFP_KERNEL);
  

• if (!binding->tx_vec) {
  

• 	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);

@@ -277,11 +306,21 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, niov->owner = owner; page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov), net_devmem_get_dma_addr(niov));

• 	if (direction == DMA_TO_DEVICE) {
  

• 		iov = &binding->tx_vec[virtual / PAGE_SIZE + i];
  

• 		iov->iov_base = niov;
  

• 		iov->iov_len = PAGE_SIZE;
  

• 	}
  

  }

virtual += len; }

• if (direction == DMA_TO_DEVICE)

• iov_iter_init(&binding->tx_iter, WRITE, binding->tx_vec,
  

• 	      virtual / PAGE_SIZE + 1, virtual);
  

• return binding;

err_free_chunks: @@ -302,6 +341,21 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, return ERR_PTR(err); } +struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id) +{

• struct net_devmem_dmabuf_binding *binding;
• rcu_read_lock();
• binding = xa_load(&net_devmem_dmabuf_bindings, id);
• if (binding) {

• if (!net_devmem_dmabuf_binding_get(binding))
  

• 	binding = NULL;
  

• }
• rcu_read_unlock();
• return binding;

+}

void dev_dmabuf_uninstall(struct net_device *dev) { struct net_devmem_dmabuf_binding *binding; @@ -332,6 +386,33 @@ void net_devmem_put_net_iov(struct net_iov *niov) net_devmem_dmabuf_binding_put(niov->owner->binding); } +struct net_devmem_dmabuf_binding * +net_devmem_get_sockc_binding(struct sock *sk, struct sockcm_cookie *sockc) +{

• struct net_devmem_dmabuf_binding *binding;
• int err = 0;
• binding = net_devmem_lookup_dmabuf(sockc->dmabuf_id);
• if (!binding || !binding->tx_vec) {

• err = -EINVAL;
  

• goto out_err;
  

• }
• if (sock_net(sk) != dev_net(binding->dev)) {

• err = -ENODEV;
  

• goto out_err;
  

• }
• iov_iter_advance(&binding->tx_iter, sockc->dmabuf_offset);
• return binding;

+out_err:

• if (binding)

• net_devmem_dmabuf_binding_put(binding);
  

• return ERR_PTR(err);

+}

/*** "Dmabuf devmem memory provider" ***/ int mp_dmabuf_devmem_init(struct page_pool *pool) diff --git a/net/core/devmem.h b/net/core/devmem.h index 54e30fea80b3..f923c77d9c45 100644 --- a/net/core/devmem.h +++ b/net/core/devmem.h @@ -11,6 +11,8 @@ #define _NET_DEVMEM_H struct netlink_ext_ack; +struct sockcm_cookie; +struct sock; struct net_devmem_dmabuf_binding { struct dma_buf *dmabuf; @@ -27,6 +29,10 @@ struct net_devmem_dmabuf_binding { * 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.

• *
  

• * net_devmem_get_net_iov() on dmabuf net_iovs will increment this
  

• * reference, making sure that that the binding remains alive until all
  

• * the net_iovs are no longer used.
  

  */ refcount_t ref;

@@ -42,6 +48,10 @@ struct net_devmem_dmabuf_binding { * active. */ u32 id;

• /* iov_iter representing all possible net_iov chunks in the dmabuf. */
• struct iov_iter tx_iter;
• struct iovec *tx_vec;

}; #if defined(CONFIG_NET_DEVMEM) @@ -66,8 +76,10 @@ struct dmabuf_genpool_chunk_owner { void __net_devmem_dmabuf_binding_free(struct net_devmem_dmabuf_binding *binding); struct net_devmem_dmabuf_binding * -net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,

•        struct netlink_ext_ack *extack);
  

+net_devmem_bind_dmabuf(struct net_device *dev,

•        enum dma_data_direction direction,
  

•        unsigned int dmabuf_fd, struct netlink_ext_ack *extack);
  

+struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id); void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding); int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx, struct net_devmem_dmabuf_binding *binding, @@ -104,10 +116,10 @@ static inline u32 net_iov_binding_id(const struct net_iov *niov) return net_iov_owner(niov)->binding->id; } -static inline void +static inline bool net_devmem_dmabuf_binding_get(struct net_devmem_dmabuf_binding *binding) {

• refcount_inc(&binding->ref);

• return refcount_inc_not_zero(&binding->ref);

} static inline void @@ -126,6 +138,9 @@ struct net_iov * net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding); void net_devmem_free_dmabuf(struct net_iov *ppiov); +struct net_devmem_dmabuf_binding * +net_devmem_get_sockc_binding(struct sock *sk, struct sockcm_cookie *sockc);

#else struct net_devmem_dmabuf_binding; @@ -144,11 +159,17 @@ __net_devmem_dmabuf_binding_free(struct net_devmem_dmabuf_binding *binding) static inline struct net_devmem_dmabuf_binding * net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd,

•        enum dma_data_direction direction,
    struct netlink_ext_ack *extack)
  

{ return ERR_PTR(-EOPNOTSUPP); } +static inline struct net_devmem_dmabuf_binding *net_devmem_lookup_dmabuf(u32 id) +{

• return NULL;

+}

static inline void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) { @@ -186,6 +207,17 @@ static inline u32 net_iov_binding_id(const struct net_iov *niov) { return 0; }

+static inline void +net_devmem_dmabuf_binding_put(struct net_devmem_dmabuf_binding *binding) +{ +}

+static inline struct net_devmem_dmabuf_binding * +net_devmem_get_sockc_binding(struct sock *sk, struct sockcm_cookie *sockc) +{

• return ERR_PTR(-EOPNOTSUPP);

+} #endif #endif /* _NET_DEVMEM_H */ diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c index 00d3d5851487..b9928bac94da 100644 --- a/net/core/netdev-genl.c +++ b/net/core/netdev-genl.c @@ -850,7 +850,8 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info) goto err_unlock; }

• binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, info->extack);

• binding = net_devmem_bind_dmabuf(netdev, DMA_FROM_DEVICE, dmabuf_fd,

• 			 info->extack);
  

  if (IS_ERR(binding)) { err = PTR_ERR(binding); goto err_unlock;

@@ -907,10 +908,68 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info) return err; } -/* stub */ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info) {

• return 0;

• struct net_devmem_dmabuf_binding *binding;
• struct list_head *sock_binding_list;
• struct net_device *netdev;
• u32 ifindex, dmabuf_fd;
• struct sk_buff *rsp;
• int err = 0;
• void *hdr;
• if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||

•    GENL_REQ_ATTR_CHECK(info, NETDEV_A_DMABUF_FD))
  

• return -EINVAL;
  

• ifindex = nla_get_u32(info->attrs[NETDEV_A_DEV_IFINDEX]);
• dmabuf_fd = nla_get_u32(info->attrs[NETDEV_A_DMABUF_FD]);
• sock_binding_list =

• genl_sk_priv_get(&netdev_nl_family, NETLINK_CB(skb).sk);
  

• if (IS_ERR(sock_binding_list))

• return PTR_ERR(sock_binding_list);
  

• rsp = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_KERNEL);
• if (!rsp)

• return -ENOMEM;
  

• hdr = genlmsg_iput(rsp, info);
• if (!hdr) {

• err = -EMSGSIZE;
  

• goto err_genlmsg_free;
  

• }
• rtnl_lock();
• netdev = __dev_get_by_index(genl_info_net(info), ifindex);
• if (!netdev || !netif_device_present(netdev)) {

• err = -ENODEV;
  

• goto err_unlock;
  

• }
• binding = net_devmem_bind_dmabuf(netdev, DMA_TO_DEVICE, dmabuf_fd,

• 			 info->extack);
  

• if (IS_ERR(binding)) {

• err = PTR_ERR(binding);
  

• goto err_unlock;
  

• }
• list_add(&binding->list, sock_binding_list);
• nla_put_u32(rsp, NETDEV_A_DMABUF_ID, binding->id);
• genlmsg_end(rsp, hdr);
• rtnl_unlock();
• return genlmsg_reply(rsp, info);
• net_devmem_unbind_dmabuf(binding);

+err_unlock:

• rtnl_unlock();

+err_genlmsg_free:

• nlmsg_free(rsp);
• return err;

} void netdev_nl_sock_priv_init(struct list_head *priv) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 815245d5c36b..eb6b41a32524 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1882,8 +1882,10 @@ EXPORT_SYMBOL_GPL(msg_zerocopy_ubuf_ops); int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, struct msghdr *msg, int len,

• 	     struct ubuf_info *uarg)
  

• 	     struct ubuf_info *uarg,
  

• 	     struct net_devmem_dmabuf_binding *binding)
  

{

• struct iov_iter *from = binding ? &binding->tx_iter : &msg->msg_iter;

For tx, I feel like this needs a copy of binding->tx_iter:

struct iov_iter tx_iter = binding->tx_iter; struct iov_iter *from = binding ? &tx_iter : &msg->msg_iter;

Or something similar (rewind?). The tx_iter is advanced in zerocopy_fill_skb_from_devmem but never reset back it seems (or I'm missing something). In you case, if you call sendmsg twice with the same offset, the second one will copy from 2*offset.

But I'd vote to move away from iov_iter on the tx side. From my initial testing, the perf wasn't great. It's basically O(n_chunks) on every message (iov_iter_advance does linear walk over the chunks). So when we call several sendmsg() with 4k chunks and increasing offset, this blows up to O(n_chunks^2). I tried to "fix" it by caching previous iter position so the next sendmsg can continue without rewinding, but it was a bit messy.

I have this simplified constant time version in [1], pls take a look and lmk what you think (zerocopy_fill_skb_from_devmem and net_devmem_get_niov_at). It is significantly faster and much simpler.

1: https://github.com/fomichev/linux/commit/3b3ad4f36771a376c204727e5a167c4993d...