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Wed, 05 Feb 2025 04:20:28 -0800 (PST) Received: from [192.168.8.100] ([148.252.128.4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c5c1016easm18630336f8f.24.2025.02.05.04.20.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Feb 2025 04:20:27 -0800 (PST) Message-ID: Date: Wed, 5 Feb 2025 12:20:34 +0000 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v3 5/6] net: devmem: Implement TX path To: Mina Almasry , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, linux-kselftest@vger.kernel.org Cc: Donald Hunter , Jakub Kicinski , "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Jonathan Corbet , Andrew Lunn , Neal Cardwell , David Ahern , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Stefan Hajnoczi , Stefano Garzarella , Shuah Khan , sdf@fomichev.me, dw@davidwei.uk, Jamal Hadi Salim , Victor Nogueira , Pedro Tammela , Samiullah Khawaja , Kaiyuan Zhang References: <20250203223916.1064540-1-almasrymina@google.com> <20250203223916.1064540-6-almasrymina@google.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20250203223916.1064540-6-almasrymina@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/3/25 22:39, Mina Almasry wrote: ... > 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, ... > 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); Instead of propagating it all the way down and carving a new path, why not reuse the existing infra? You already hook into where ubuf is allocated, you can stash the binding in there. And zerocopy_fill_skb_from_devmem can implement ->sg_from_iter, see __zerocopy_sg_from_iter(). ... > 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 @@ > +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); Unless I missed it somewhere it needs to check that the iter is iovec based. > + 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); As mentioned above, you can implement this callback. The callback can also be moved into ubuf_info ops if that's more convenient, I had patches stashed for that. > + 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; ... > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index 0d704bda6c41..44198ae7e44c 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -1051,6 +1051,7 @@ int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *copied, > > int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) > { > + struct net_devmem_dmabuf_binding *binding = NULL; > struct tcp_sock *tp = tcp_sk(sk); > struct ubuf_info *uarg = NULL; > struct sk_buff *skb; > @@ -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) { It's better to be mutually exclusive with msg->msg_ubuf, the callers have expectations about the buffers used. And you likely don't want to mix it with normal MSG_ZEROCOPY in a single skb and/or ubuf_info, you can force reallocation of ubuf_info here. > + binding = net_devmem_get_binding(sk, sockc.dmabuf_id); > + if (IS_ERR(binding)) { > + err = PTR_ERR(binding); > + binding = NULL; > + goto out_err; > + } > + } -- Pavel Begunkov