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virtio_net: checksum offloading handling fix

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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: 4f49129be6 ("virtio-net: Set RXCSUM feature if GUEST_CSUM is available")
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Heng Qi 2024-06-17 21:15:23 +08:00 committed by David S. Miller
parent 7be4cb7189
commit 604141c036
1 changed files with 10 additions and 2 deletions
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12
drivers/net/virtio_net.c
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@ -5666,8 +5666,16 @@ static int virtnet_probe(struct virtio_device *vdev)
dev->features |= dev->hw_features & NETIF_F_ALL_TSO;
/* (!csum && gso) case will be fixed by register_netdev() */
}
if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_CSUM))
dev->features |= NETIF_F_RXCSUM;
/* 1. With VIRTIO_NET_F_GUEST_CSUM negotiation, the driver doesn't
* need to calculate checksums for partially checksummed packets,
* as they're considered valid by the upper layer.
* 2. Without VIRTIO_NET_F_GUEST_CSUM negotiation, the driver only
* receives fully checksummed packets. The device may assist in
* validating these packets' checksums, so the driver won't have to.
*/
dev->features |= NETIF_F_RXCSUM;
if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
dev->features |= NETIF_F_GRO_HW;