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([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85c6dc25sm9228007f8f.33.2026.07.22.13.20.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Jul 2026 13:20:45 -0700 (PDT) Message-ID: Date: Wed, 22 Jul 2026 21:20:47 +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: Mina Almasry Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org 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: 8bit On 7/22/26 20:49, Mina Almasry wrote: > On Wed, Jul 22, 2026 at 3:59 AM 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 > > It's true that we don't support mixing niov types and doing so would > blow up, but this is an unnecessary defensive check imo. The calling > code should not (and does not, I hope) have an edge case where it > tries to mix and match niov types. Nope, that can easily happen. > Maybe a DEBUG_NET_WARN_ON check to help catch bugs in the calling code > may be fine? > > Also we don't really support mixing different niov sub-types in an skb > (like IO_URING + DMABUF) afaict, so might as well go the extra mile > and check that it's all devmem niovs specifically. All those type intermixing rules might be flaky, maybe we should start with DEBUG_NET_WARN_ON, but at least for tx from a quick look it's handled by ubuf_info checks. > And might as well put the check in skb_add_rx_frag_netmem. It's the > same situation on RX, we don't support mixing there (and I hope no > code path leads to mixing today). A DEBUG_NET_WARN_ON there might be a very good idea, I agree. -- Pavel Begunkov