linux-kernel - Re: [PATCH net-next v13 4/9] net: devmem: Implement TX path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fd7f21d9-3f45-4f68-85cb-dd160a0a95ca@redhat.com>
Date: Fri, 2 May 2025 13:51:04 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 io-uring@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, Donald Hunter <donald.hunter@...il.com>,
 Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>,
 Jeroen de Borst <jeroendb@...gle.com>,
 Harshitha Ramamurthy <hramamurthy@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Willem de Bruijn
 <willemb@...gle.com>, Jens Axboe <axboe@...nel.dk>,
 Pavel Begunkov <asml.silence@...il.com>, David Ahern <dsahern@...nel.org>,
 Neal Cardwell <ncardwell@...gle.com>, "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Stefan Hajnoczi <stefanha@...hat.com>,
 Stefano Garzarella <sgarzare@...hat.com>, Shuah Khan <shuah@...nel.org>,
 sdf@...ichev.me, dw@...idwei.uk, Jamal Hadi Salim <jhs@...atatu.com>,
 Victor Nogueira <victor@...atatu.com>, Pedro Tammela
 <pctammela@...atatu.com>, Samiullah Khawaja <skhawaja@...gle.com>,
 Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [PATCH net-next v13 4/9] net: devmem: Implement TX path

On 5/2/25 1:47 PM, Paolo Abeni wrote:
> On 4/29/25 5:26 AM, Mina Almasry wrote:
>> Augment dmabuf binding to be able to handle TX. Additional to all the RX
>> binding, we also create tx_vec needed for the TX path.
>>
>> Provide API for sendmsg to be able to send dmabufs bound to this device:
>>
>> - Provide a new dmabuf_tx_cmsg which includes the dmabuf to send from.
>> - MSG_ZEROCOPY with SCM_DEVMEM_DMABUF cmsg indicates send from dma-buf.
>>
>> Devmem is uncopyable, so piggyback off the existing MSG_ZEROCOPY
>> implementation, while disabling instances where MSG_ZEROCOPY falls back
>> to copying.
>>
>> We additionally pipe the binding down to the new
>> zerocopy_fill_skb_from_devmem which fills a TX skb with net_iov netmems
>> instead of the traditional page netmems.
>>
>> We also special case skb_frag_dma_map to return the dma-address of these
>> dmabuf net_iovs instead of attempting to map pages.
>>
>> The TX path may release the dmabuf in a context where we cannot wait.
>> This happens when the user unbinds a TX dmabuf while there are still
>> references to its netmems in the TX path. In that case, the netmems will
>> be put_netmem'd from a context where we can't unmap the dmabuf, Resolve
>> this by making __net_devmem_dmabuf_binding_free schedule_work'd.
>>
>> Based on work by Stanislav Fomichev <sdf@...ichev.me>. A lot of the meat
>> of the implementation came from devmem TCP RFC v1[1], which included the
>> TX path, but Stan did all the rebasing on top of netmem/net_iov.
>>
>> Cc: Stanislav Fomichev <sdf@...ichev.me>
>> Signed-off-by: Kaiyuan Zhang <kaiyuanz@...gle.com>
>> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>> Acked-by: Stanislav Fomichev <sdf@...ichev.me>
> 
> I'm sorry for the late feedback. A bunch of things I did not notice
> before...

The rest LGTM, and my feedback here ranges from nit to corner-cases, so
we are probably better off with a follow-up than with a repost, other
opinions welcome!

/P