netdev - Re: [PATCH 1/2] virtio_net: checksum offloading handling fix

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Date: Mon, 17 Jun 2024 15:34:55 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev,
	Thomas Huth <thuth@...ux.vnet.ibm.com>,
	Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH 1/2] virtio_net: checksum offloading handling fix

Mon, Jun 17, 2024 at 03:15:23PM CEST, hengqi@...ux.alibaba.com wrote:
>In virtio spec 0.95, VIRTIO_NET_F_GUEST_CSUM was designed to handle
>partially checksummed packets, and the validation of fully checksummed
>packets by the device is independent of VIRTIO_NET_F_GUEST_CSUM
>negotiation. However, the specification erroneously stated:
>
>  "If VIRTIO_NET_F_GUEST_CSUM is not negotiated, the device MUST set flags
>   to zero and SHOULD supply a fully checksummed packet to the driver."
>
>This statement is inaccurate because even without VIRTIO_NET_F_GUEST_CSUM
>negotiation, the device can still set the VIRTIO_NET_HDR_F_DATA_VALID flag.
>Essentially, the device can facilitate the validation of these packets'
>checksums - a process known as RX checksum offloading - removing the need
>for the driver to do so.
>
>This scenario is currently not implemented in the driver and requires
>correction. The necessary specification correction[1] has been made and
>approved in the virtio TC vote.
>[1] https://lists.oasis-open.org/archives/virtio-comment/202401/msg00011.html
>
>Fixes: 4f49129be6fa ("virtio-net: Set RXCSUM feature if GUEST_CSUM is available")
>Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>