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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482c9bfd2c6sm7438382f8f.24.2026.08.24.01.27.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2026 01:27:25 -0700 (PDT) Date: Mon, 24 Aug 2026 09:27:24 +0100 From: David Laight To: Mina Almasry Cc: Pavel Begunkov , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org Subject: Re: [PATCH net 1/1] tcp: reject non zerocopy devmem tx Message-ID: <20260824092724.1b62af12@pumpkin> In-Reply-To: References: X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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: quoted-printable On Sun, 23 Aug 2026 08:58:32 -0700 Mina Almasry wrote: > On Sat, Aug 22, 2026 at 3:57=E2=80=AFAM Pavel Begunkov wrote: > > > > Device memory send doesn't work without zero copy, prevent > > tcp_sendmsg_locked() from falling back to the copy mode for devmem in > > case there is no NETIF_F_SG. Currently, it'd try to copy from iovec > > filled with dma-buf offsets, which would normally fail with EFAULT, but > > it's still better to handle it more explicitly. A recent net-iov / page > > mixing fix also needs this patch. > > > > Fixes: bd61848900bff ("net: devmem: Implement TX path") > > Signed-off-by: Pavel Begunkov > > --- > > net/ipv4/tcp.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > > index 455441f1b694..f403830af65f 100644 > > --- a/net/ipv4/tcp.c > > +++ b/net/ipv4/tcp.c > > @@ -1162,6 +1162,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct m= sghdr *msg, size_t size) > > binding =3D NULL; > > goto out_err; > > } > > + if (zc !=3D MSG_ZEROCOPY) { > > + err =3D -EOPNOTSUPP; > > + goto out_err; > > + } > > } > > } > > } else if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES) && size)= { > > -- > > 2.54.0 > > =20 >=20 > Thanks, I was indeed putting together patches to fix all the > pre-existing issues. I think the code assumes devmem send means > binding is not NULL, and the fact that we efault on copying is lucky, > we should not even attempt copying. >=20 > How about we reduce the complexity of an already-long > tcp_sendmsg_locked function by combining this check with the other > ones? I was thinking this: >=20 > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index b4237d0e994d6..1e34f50770446 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -1170,7 +1170,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct > msghdr *msg, size_t size) > } >=20 > if (!sockc_err && sockc.dmabuf_id && > - (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY))) { > + (!(flags & MSG_ZEROCOPY) || !sock_flag(sk, SOCK_ZEROCOPY) || > + zc !=3D MSG_ZEROCOPY)) { That might be more readable with the ! moved outside the (): > + !((flags & MSG_ZEROCOPY) && sock_flag(sk, SOCK_ZEROCOPY) && > + zc =3D=3D MSG_ZEROCOPY)) { David > err =3D -EINVAL; > goto out_err; > } >=20 > It will return EINVAL instead of EOPNOTSUPP but I think that is OK. >=20