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[35.236.206.96]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b9ac2bbfc5sm650803285a.1.2024.12.26.13.52.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Dec 2024 13:52:35 -0800 (PST) Date: Thu, 26 Dec 2024 16:52:34 -0500 From: Willem de Bruijn To: Mina Almasry , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Mina Almasry , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Donald Hunter , Jonathan Corbet , Andrew Lunn , David Ahern , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?B?RXVnZW5pbyBQw6lyZXo=?= , Stefan Hajnoczi , Stefano Garzarella , Shuah Khan , Kaiyuan Zhang , Pavel Begunkov , Willem de Bruijn , Samiullah Khawaja , Stanislav Fomichev , Joe Damato , dw@davidwei.uk Message-ID: <676dd022d1388_1d346b2947@willemb.c.googlers.com.notmuch> In-Reply-To: <20241221004236.2629280-6-almasrymina@google.com> References: <20241221004236.2629280-1-almasrymina@google.com> <20241221004236.2629280-6-almasrymina@google.com> Subject: Re: [PATCH RFC net-next v1 5/5] net: devmem: Implement TX path Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit 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 . 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 > > --- > 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(-) > > +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; On error, should caller skb_zerocopy_iter_stream rewind from, rather than (or as well as) msg->msg_iter? > + > + 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); What does this do if sendmsg is called with NULL as buffer? > + > + 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); > 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(); > + What precisely does this protect? synchronize_net() ensures no packet is in flight inside an rcu readside section. But a packet can still be in flight, such as posted to the device or queued in a qdisc. > 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, instead of open coding this computation repeatedly, consider a local variable. And parentheses and maybe round_up(). > + 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]; why does this start counting at virtual / PAGE_SIZE, rather than 0? > + 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); This lookup is from global xarray net_devmem_dmabuf_bindings. Is there a check that the socket is sending out through the device to which this dmabuf was bound with netlink? Should there be? (e.g., SO_BINDTODEVICE). > + 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" ***/ > > @@ -1063,6 +1064,15 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) > > flags = msg->msg_flags; > > + sockcm_init(&sockc, sk); > + if (msg->msg_controllen) { > + err = sock_cmsg_send(sk, msg, &sockc); > + if (unlikely(err)) { > + err = -EINVAL; > + goto out_err; > + } > + } > + > if ((flags & MSG_ZEROCOPY) && size) { > if (msg->msg_ubuf) { > uarg = msg->msg_ubuf; > @@ -1080,6 +1090,15 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) > else > uarg_to_msgzc(uarg)->zerocopy = 0; > } > + > + if (sockc.dmabuf_id != 0) { > + binding = net_devmem_get_sockc_binding(sk, &sockc); > + if (IS_ERR(binding)) { > + err = PTR_ERR(binding); > + binding = NULL; > + goto out_err; > + } > + }