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

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Date: Tue, 18 Jun 2024 11:01:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev, 
	Thomas Huth <thuth@...ux.vnet.ibm.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

On Mon, Jun 17, 2024 at 9:15 PM Heng Qi <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>
> ---

Acked-by: Jason Wang <jasowang@...hat.com>

(Should we manually do checksum if RXCUSM is disabled?)

Thanks