Re: [PATCH RFC net-next v2 5/6] net: devmem: Implement TX path

On 01/30, Mina Almasry wrote:

Augment dmabuf binding to be able to handle TX. Additional to all the RX binding, we also create tx_vec 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.
• 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 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

---

v2:

• Remove dmabuf_offset from the dmabuf cmsg.
• Update zerocopy_fill_skb_from_devmem to interpret the iov_base/iter_iov_addr as the offset into the dmabuf to send from (Stan).
• Remove the confusing binding->tx_iter which is not needed if we interpret the iov_base/iter_iov_addr as offset into the dmabuf (Stan).
• Remove check for binding->sgt and binding->sgt->nents in dmabuf binding.
• Simplify the calculation of binding->tx_vec.
• Check in net_devmem_get_binding that the binding we're returning has ifindex matching the sending socket (Willem).

---

include/linux/skbuff.h | 15 +++- include/net/sock.h | 1 + include/uapi/linux/uio.h | 6 +- net/core/datagram.c | 41 ++++++++++- net/core/devmem.c | 96 +++++++++++++++++++++++-- net/core/devmem.h | 42 +++++++++-- net/core/netdev-genl.c | 65 ++++++++++++++++- net/core/skbuff.c | 6 +- net/core/sock.c | 8 +++ net/ipv4/tcp.c | 36 +++++++--- net/vmw_vsock/virtio_transport_common.c | 3 +- 11 files changed, 285 insertions(+), 34 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index bb2b751d274a..3ff8f568c382 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1711,9 +1711,12 @@ 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,
  

• 	    struct net_devmem_dmabuf_binding *binding);
  

int zerocopy_fill_skb_from_iter(struct sk_buff *skb, struct iov_iter *from, size_t length); @@ -1721,12 +1724,14 @@ 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,

• 		       NULL);
  

} 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 +3702,10 @@ 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 8036b3b79cd8..09eb918525b6 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1822,6 +1822,7 @@ struct sockcm_cookie { u32 tsflags; u32 ts_opt_id; u32 priority;

• u32 dmabuf_id;

}; 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..866bd5dfe39f 100644 --- a/include/uapi/linux/uio.h +++ b/include/uapi/linux/uio.h @@ -38,10 +38,14 @@ struct dmabuf_token { __u32 token_count; }; +struct dmabuf_tx_cmsg {

• __u32 dmabuf_id;

+};

/*

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

*/

#define UIO_FASTIOV 8 #define UIO_MAXIOV 1024 diff --git a/net/core/datagram.c b/net/core/datagram.c index f0693707aece..c989606ff58d 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 +694,42 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb, return 0; } +static int +zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,

• 	      int length,
  

• 	      struct net_devmem_dmabuf_binding *binding)
  

+{

• int i = skb_shinfo(skb)->nr_frags;
• size_t virt_addr, size, off;
• struct net_iov *niov;
• while (length && iov_iter_count(from)) {

• if (i == MAX_SKB_FRAGS)
  

• 	return -EMSGSIZE;
  

• virt_addr = (size_t)iter_iov_addr(from);
  

• niov = net_devmem_get_niov_at(binding, virt_addr, &off, &size);
  

• if (!niov)
  

• 	return -EFAULT;
  

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

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

• get_netmem(net_iov_to_netmem(niov));
  

• skb_add_rx_frag_netmem(skb, i, net_iov_to_netmem(niov), off,
  

• 		       size, PAGE_SIZE);
  

• iov_iter_advance(from, size);
  

• length -= size;
  

• i++;
  

• }
• 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,
  

• 	    struct net_devmem_dmabuf_binding *binding)
  

{ unsigned long orig_size = skb->truesize; unsigned long truesize; @@ -702,6 +737,8 @@ 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(binding))

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

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

@@ -735,7 +772,7 @@ 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 20985a570662..796338b1599e 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -16,6 +16,7 @@ #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" @@ -64,8 +65,10 @@ 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) @@ -110,6 +113,13 @@ 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);

@@ -123,8 +133,6 @@ 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);

} @@ -185,8 +193,9 @@ 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; @@ -229,7 +238,7 @@ 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");

@@ -240,13 +249,22 @@ net_devmem_bind_dmabuf(struct net_device *dev, unsigned int dmabuf_fd, * 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));
  

• binding->chunk_pool = gen_pool_create(PAGE_SHIFT,

• 			      dev_to_node(&dev->dev));
  

  if (!binding->chunk_pool) { err = -ENOMEM; goto err_unmap; }

• if (direction == DMA_TO_DEVICE) {

• binding->tx_vec = kcalloc(dmabuf->size / PAGE_SIZE,
  

• 			  sizeof(struct net_iov *), GFP_KERNEL);
  

Let's make this kvcalloc (and kvfree in the release path)? Otherwise we'll get ENOMEM here for a reasonably sized dmabufs..

The rest looks good, I'll try to run it on my side today/tomorrow..