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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Alex Shi , Yanteng Si , Dongliang Mu , Michael Chan , Pavan Chebbi , Joshua Washington , Harshitha Ramamurthy , Saeed Mahameed , Tariq Toukan , Mark Bloch , Leon Romanovsky , Alexander Duyck , kernel-team@meta.com, Daniel Borkmann , Nikolay Aleksandrov , Shuah Khan , dw@davidwei.uk, mohsin.bashr@gmail.com, willemb@google.com, jiang.kun2@zte.com.cn, xu.xin16@zte.com.cn, wang.yaxin@zte.com.cn, netdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Stanislav Fomichev , Mina Almasry , Bobby Eshleman Subject: Re: [PATCH net-next v3 2/8] net: netkit: declare NETMEM_TX_NO_DMA mode Message-ID: References: <20260507-tcp-dm-netkit-v3-0-52821445867c@meta.com> <20260507-tcp-dm-netkit-v3-2-52821445867c@meta.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260507-tcp-dm-netkit-v3-2-52821445867c@meta.com> On 05/07, Bobby Eshleman wrote: > From: Bobby Eshleman > > Some virtual devices like netkit (or ifb) never DMA and never touch frag > contents, they just forward the skb to another device. They are unable > to forward unreadable skbs, however, because they fail to pass TX > validation checks on dev->netmem_tx. The existing two-state > NETMEM_TX_NONE / NETMEM_TX_DMA doesn't give the TX validator enough > information to differentiate devices that will attempt DMA on the > unreadable skb from those that will simply route it untouched. > > Add a third mode to the enum so drivers can indicate 1) if they have > netmem TX support, and 2) if they do, whether they are DMA-capable: > > NETMEM_TX_NO_DMA - pass-through, device never DMAs > > Widen dev->netmem_tx from a 1-bit field to 2 bits to fit the new value, > and declare netkit as NETMEM_TX_NO_DMA. Devmem TX support over these > devices comes in a follow-up patch. > > Signed-off-by: Bobby Eshleman Acked-by: Stanislav Fomichev