4.19-stable review patch. If anyone has any objections, please let me know.
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From: Heng Qi hengqi@linux.alibaba.com
[ Upstream commit 604141c036e1b636e2a71cf6e1aa09d1e45f40c2 ]
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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/virtio_net.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
--- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -3020,8 +3020,15 @@ static int virtnet_probe(struct virtio_d 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;
dev->vlan_features = dev->features;