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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, Mina Almasry Subject: Re: [PATCH net 1/1] net: devmem: prevent net-iov / page mixing Message-ID: References: <06f0d5ce07dd8593a69239cfa56745cb9c7d957c.1784717791.git.asml.silence@gmail.com> <5c3c34de-7b34-4122-a792-e91b48858f2f@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5c3c34de-7b34-4122-a792-e91b48858f2f@gmail.com> On Wed, Jul 22, 2026 at 07:58:27PM +0100, Pavel Begunkov wrote: > On 7/22/26 18:59, Bobby Eshleman wrote: > > On Wed, Jul 22, 2026 at 11:58:46AM +0100, Pavel Begunkov wrote: > > > We should either have net_iov or page backed frags in a single skb, > > > otherwise it blows up down the stack. Don't allow mixing in > > > zerocopy_fill_skb_from_devmem(). > > > > > > Fixes: bd61848900bff ("net: devmem: Implement TX path") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Pavel Begunkov > > > --- > > > net/core/datagram.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/net/core/datagram.c b/net/core/datagram.c > > > index c285c6465923..35febc1c25fa 100644 > > > --- a/net/core/datagram.c > > > +++ b/net/core/datagram.c > > > @@ -712,6 +712,9 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from, > > > size_t virt_addr, size, off; > > > struct net_iov *niov; > > > + if (i && skb_frags_readable(skb)) > > > + return -EEXIST; > > > > Are we trying to hit the -EEXIST handler in tcp_sendmsg_locked() so that > > we start a new skb? If so, I think we might need to plumb this -EEXIST > > case through skb_zerocopy_iter_stream() too? > > Easier to EFAULT. It'd more consistent, and I don't care how tcp takes > it specifically. > > -- > Pavel Begunkov > One socket is allowed to queue non-devmem followed by devmem, and EFAULT will break this case. I think EEXIST is right, just needs to propagate up. Best, Bobby