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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Donald Hunter , Jonathan Corbet , Andrew Lunn , David Ahern , Stefan Hajnoczi , Stefano Garzarella , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Shuah Khan , sdf@fomichev.me, asml.silence@gmail.com, dw@davidwei.uk, Jamal Hadi Salim , Victor Nogueira , Pedro Tammela , Kaiyuan Zhang Subject: Re: [PATCH RFC net-next v2 5/6] net: devmem: Implement TX path Message-ID: References: <20250130211539.428952-1-almasrymina@google.com> <20250130211539.428952-6-almasrymina@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250130211539.428952-6-almasrymina@google.com> 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 . 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 > Signed-off-by: Kaiyuan Zhang > Signed-off-by: Mina Almasry > > > --- > > 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 > #include > > +#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 > #include > #include > +#include > #include > > #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..