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Message-ID: <67a3de8559316_17745c29479@willemb.c.googlers.com.notmuch>
Date: Wed, 05 Feb 2025 16:56:21 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Mina Almasry <almasrymina@...gle.com>,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
kvm@...r.kernel.org,
virtualization@...ts.linux.dev,
linux-kselftest@...r.kernel.org
Cc: Mina Almasry <almasrymina@...gle.com>,
Donald Hunter <donald.hunter@...il.com>,
Jakub Kicinski <kuba@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>,
Jonathan Corbet <corbet@....net>,
Andrew Lunn <andrew+netdev@...n.ch>,
Neal Cardwell <ncardwell@...gle.com>,
David Ahern <dsahern@...nel.org>,
"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,
asml.silence@...il.com,
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 v3 5/6] net: devmem: Implement TX path
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.
>
> 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>
>
>
> ---
>
> v3:
> - Use kvmalloc_array instead of kcalloc (Stan).
> - Fix unreachable code warning (Simon).
>
> v2:
> - Remove dmabuf_offset from the dmabuf cmsg.
> - Update zerocopy_fill_skb_from_devmem to interpret the
> iov_base/iter_iov_addr as the offset into the dmabuf to send from
> (Stan).
> - Remove the confusing binding->tx_iter which is not needed if we
> interpret the iov_base/iter_iov_addr as offset into the dmabuf (Stan).
> - Remove check for binding->sgt and binding->sgt->nents in dmabuf
> binding.
> - Simplify the calculation of binding->tx_vec.
> - Check in net_devmem_get_binding that the binding we're returning
> has ifindex matching the sending socket (Willem).
> ---
> include/linux/skbuff.h | 15 +++-
> include/net/sock.h | 1 +
> include/uapi/linux/uio.h | 6 +-
> net/core/datagram.c | 41 ++++++++++-
> net/core/devmem.c | 97 +++++++++++++++++++++++--
> net/core/devmem.h | 42 ++++++++++-
> net/core/netdev-genl.c | 64 +++++++++++++++-
> net/core/skbuff.c | 6 +-
> net/core/sock.c | 8 ++
> net/ipv4/tcp.c | 36 ++++++---
> net/vmw_vsock/virtio_transport_common.c | 3 +-
> 11 files changed, 285 insertions(+), 34 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index bb2b751d274a..3ff8f568c382 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1711,9 +1711,12 @@ struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
>
> void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
>
> +struct net_devmem_dmabuf_binding;
> +
> int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk,
> struct sk_buff *skb, struct iov_iter *from,
> - size_t length);
> + size_t length,
> + struct net_devmem_dmabuf_binding *binding);
>
> int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
> struct iov_iter *from, size_t length);
> @@ -1721,12 +1724,14 @@ int zerocopy_fill_skb_from_iter(struct sk_buff *skb,
> static inline int skb_zerocopy_iter_dgram(struct sk_buff *skb,
> struct msghdr *msg, int len)
> {
> - return __zerocopy_sg_from_iter(msg, skb->sk, skb, &msg->msg_iter, len);
> + return __zerocopy_sg_from_iter(msg, skb->sk, skb, &msg->msg_iter, len,
> + NULL);
> }
>
> int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
> struct msghdr *msg, int len,
> - struct ubuf_info *uarg);
> + struct ubuf_info *uarg,
> + struct net_devmem_dmabuf_binding *binding);
>
> /* Internal */
> #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
> @@ -3697,6 +3702,10 @@ static inline dma_addr_t __skb_frag_dma_map(struct device *dev,
> size_t offset, size_t size,
> enum dma_data_direction dir)
> {
> + if (skb_frag_is_net_iov(frag)) {
> + return netmem_to_net_iov(frag->netmem)->dma_addr + offset +
> + frag->offset;
> + }
> return dma_map_page(dev, skb_frag_page(frag),
> skb_frag_off(frag) + offset, size, dir);
> }
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 8036b3b79cd8..09eb918525b6 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1822,6 +1822,7 @@ struct sockcm_cookie {
> u32 tsflags;
> u32 ts_opt_id;
> u32 priority;
> + u32 dmabuf_id;
> };
>
> static inline void sockcm_init(struct sockcm_cookie *sockc,
> diff --git a/include/uapi/linux/uio.h b/include/uapi/linux/uio.h
> index 649739e0c404..866bd5dfe39f 100644
> --- a/include/uapi/linux/uio.h
> +++ b/include/uapi/linux/uio.h
> @@ -38,10 +38,14 @@ struct dmabuf_token {
> __u32 token_count;
> };
>
> +struct dmabuf_tx_cmsg {
> + __u32 dmabuf_id;
> +};
> +
Why a wrapper struct instead of just __u32?
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