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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85c63678sm7860766f8f.29.2026.07.22.11.58.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Jul 2026 11:58:25 -0700 (PDT) Message-ID: <5c3c34de-7b34-4122-a792-e91b48858f2f@gmail.com> Date: Wed, 22 Jul 2026 19:58:27 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 1/1] net: devmem: prevent net-iov / page mixing To: Bobby Eshleman Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, Mina Almasry References: <06f0d5ce07dd8593a69239cfa56745cb9c7d957c.1784717791.git.asml.silence@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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