netdev - Re: [PATCH RFC v3 6/8] virtio_net: enable gso over UDP tunnel support.

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Message-ID: <91fcc95c-8527-4b4c-9c19-6a8dfea010ac@redhat.com>
Date: Thu, 12 Jun 2025 12:17:56 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org, Willem de Bruijn
 <willemdebruijn.kernel@...il.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Yuri Benditovich <yuri.benditovich@...nix.com>,
 Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: Re: [PATCH RFC v3 6/8] virtio_net: enable gso over UDP tunnel
 support.

On 6/12/25 6:05 AM, Jason Wang wrote:
> On Fri, Jun 6, 2025 at 7:46 PM Paolo Abeni <pabeni@...hat.com> wrote:
>>
>> If the related virtio feature is set, enable transmission and reception
>> of gso over UDP tunnel packets.
>>
>> Most of the work is done by the previously introduced helper, just need
>> to determine the UDP tunnel features inside the virtio_net_hdr and
>> update accordingly the virtio net hdr size.
>>
>> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
>> ---
>> v2 -> v3:
>>   - drop the VIRTIO_HAS_EXTENDED_FEATURES conditionals
>>
>> v1 -> v2:
>>   - test for UDP_TUNNEL_GSO* only on builds with extended features support
>>   - comment indentation cleanup
>>   - rebased on top of virtio helpers changes
>>   - dump more information in case of bad offloads
>> ---
>>  drivers/net/virtio_net.c | 70 +++++++++++++++++++++++++++++++---------
>>  1 file changed, 54 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 18ad50de4928..0b234f318e39 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -78,15 +78,19 @@ static const unsigned long guest_offloads[] = {
>>         VIRTIO_NET_F_GUEST_CSUM,
>>         VIRTIO_NET_F_GUEST_USO4,
>>         VIRTIO_NET_F_GUEST_USO6,
>> -       VIRTIO_NET_F_GUEST_HDRLEN
>> +       VIRTIO_NET_F_GUEST_HDRLEN,
>> +       VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_MAPPED,
>> +       VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM_MAPPED,
>>  };
>>
>>  #define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
>> -                               (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
>> -                               (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
>> -                               (1ULL << VIRTIO_NET_F_GUEST_UFO)  | \
>> -                               (1ULL << VIRTIO_NET_F_GUEST_USO4) | \
>> -                               (1ULL << VIRTIO_NET_F_GUEST_USO6))
>> +                       (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_UFO)  | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_USO4) | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_USO6) | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_MAPPED) | \
>> +                       (1ULL << VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM_MAPPED))
>>
>>  struct virtnet_stat_desc {
>>         char desc[ETH_GSTRING_LEN];
>> @@ -436,9 +440,14 @@ struct virtnet_info {
>>         /* Packet virtio header size */
>>         u8 hdr_len;
>>
>> +       /* UDP tunnel support */
>> +       u8 tnl_offset;
>> +
>>         /* Work struct for delayed refilling if we run low on memory. */
>>         struct delayed_work refill;
>>
>> +       bool rx_tnl_csum;
>> +
>>         /* Is delayed refill enabled? */
>>         bool refill_enabled;
>>
>> @@ -2531,14 +2540,22 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *
>>         if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report)
>>                 virtio_skb_set_hash(&hdr->hash_v1_hdr, skb);
>>
>> -       if (flags & VIRTIO_NET_HDR_F_DATA_VALID)
>> -               skb->ip_summed = CHECKSUM_UNNECESSARY;
>> +       /* restore the received value */
> 
> Nit: this comment seems to be redundant
> 
>> +       hdr->hdr.flags = flags;
>> +       if (virtio_net_chk_data_valid(skb, &hdr->hdr, vi->rx_tnl_csum)) {
> 
> Nit: this function did more than just check DATA_VALID, we probably
> need a better name.

What about virtio_net_handle_csum_offload()?

> 
>> +               net_warn_ratelimited("%s: bad csum: flags: %x, gso_type: %x rx_tnl_csum %d\n",
>> +                                    dev->name, hdr->hdr.flags,
>> +                                    hdr->hdr.gso_type, vi->rx_tnl_csum);
>> +               goto frame_err;
>> +       }
>>
>> -       if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
>> -                                 virtio_is_little_endian(vi->vdev))) {
>> -               net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n",
>> +       if (virtio_net_hdr_tnl_to_skb(skb, &hdr->hdr, vi->tnl_offset,
> 
> I wonder why virtio_net_chk_data_valid() is not part of the
> virtio_net_hdr_tnl_to_skb().

It can't be part of virtio_net_hdr_tnl_to_skb(), as hdr to skb
conversion is actually not symmetric with respect to the checksum - only
the driver handles DATA_VALID.

Tun must not call virtio_net_chk_data_valid()  (or whatever different
name will use).

/P