Re: [PATCH RFC v3 12/13] net: implement tunnel probing

[Paolo Abeni <pabeni@redhat.com>]

On 7/22/25 5:50 AM, Jason Wang wrote:
> On Fri, Jul 18, 2025 at 4:54 PM Paolo Abeni <pabeni@redhat.com> wrote:
>> Tap devices support GSO over UDP tunnel offload. Probe for such
>> feature in a similar manner to other offloads.
>>
>> GSO over UDP tunnel needs to be enabled in addition to a "plain"
>> offload (TSO or USO).
>>
>> No need to check separately for the outer header checksum offload:
>> the kernel is going to support both of them or none.
>>
>> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
>> ---
>> v2 -> v3:
>>   - use bool type for tap_probe_has_tunnel()
>>   - rebased on top of 2deec9ab7d ("virtio-net: Move
>>         virtio_net_get_features() down")
>>   - _array -> _ex
>>
>> v1 -> v2:
>>   - peer_has_tunnel return a bool
>>   - move TUN_F definition in net/tun-linux.h
>> ---
>>  hw/net/virtio-net.c | 37 +++++++++++++++++++++++++++++++++++++
>>  include/net/net.h   |  3 +++
>>  net/net.c           |  9 +++++++++
>>  net/tap-bsd.c       |  5 +++++
>>  net/tap-linux.c     | 11 +++++++++++
>>  net/tap-linux.h     |  9 +++++++++
>>  net/tap-solaris.c   |  5 +++++
>>  net/tap-stub.c      |  5 +++++
>>  net/tap.c           | 11 +++++++++++
>>  net/tap_int.h       |  1 +
>>  10 files changed, 96 insertions(+)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 53413ec4d5..70c85f7f77 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -649,6 +649,15 @@ static int peer_has_uso(VirtIONet *n)
>>      return qemu_has_uso(qemu_get_queue(n->nic)->peer);
>>  }
>>
>> +static bool peer_has_tunnel(VirtIONet *n)
> 
> Nit: it looks better to use peer_has_udp_gso_tunnel().
> 
>> +{
>> +    if (!peer_has_vnet_hdr(n)) {
>> +        return false;
>> +    }
>> +
>> +    return qemu_has_tunnel(qemu_get_queue(n->nic)->peer);
>> +}
>> +
>>  static void virtio_net_set_mrg_rx_bufs(VirtIONet *n, int mergeable_rx_bufs,
>>                                         int version_1, int hash_report)
>>  {
>> @@ -3070,6 +3079,13 @@ static void virtio_net_get_features(VirtIODevice *vdev, uint64_t *features,
>>          virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
>>          virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
>>
>> +        virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
>> +        virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
>> +        virtio_clear_feature_ex(features,
>> +                                VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
>> +        virtio_clear_feature_ex(features,
>> +                                VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
>> +
>>          virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
>>      }
>>
>> @@ -3083,6 +3099,15 @@ static void virtio_net_get_features(VirtIODevice *vdev, uint64_t *features,
>>          virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
>>      }
>>
>> +    if (!peer_has_tunnel(n)) {
>> +        virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
>> +        virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
>> +        virtio_clear_feature_ex(features,
>> +                                VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
>> +        virtio_clear_feature_ex(features,
>> +                                VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
>> +    }
>> +
>>      if (!get_vhost_net(nc->peer)) {
>>          if (!use_own_hash) {
>>              virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
>> @@ -4137,6 +4162,10 @@ static const VMStateDescription vmstate_virtio_net = {
>>      .dev_unplug_pending = dev_unplug_pending,
>>  };
>>
>> +#define DEFINE_PROP_FEATURE(_name, _state, _field, _bit, _defval)   \
>> +    DEFINE_PROP_BIT64(_name, _state, _field[VIRTIO_DWORD(_bit)],    \
>> +                      (_bit) % 64, _defval)
>> +
>>  static const Property virtio_net_properties[] = {
>>      DEFINE_PROP_BIT64("csum", VirtIONet, host_features,
>>                      VIRTIO_NET_F_CSUM, true),
>> @@ -4245,6 +4274,14 @@ static const Property virtio_net_properties[] = {
>>                                    rss_data.specified_hash_types,
>>                                    VIRTIO_NET_HASH_REPORT_UDPv6_EX - 1,
>>                                    ON_OFF_AUTO_AUTO),
>> +    DEFINE_PROP_FEATURE("host_tunnel", VirtIONet, host_features_ex,
>> +                        VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO, true),
>> +    DEFINE_PROP_FEATURE("host_tunnel_csum", VirtIONet, host_features_ex,
>> +                        VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM, true),
>> +    DEFINE_PROP_FEATURE("guest_tunnel", VirtIONet, host_features_ex,
>> +                        VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO, true),
>> +    DEFINE_PROP_FEATURE("guest_tunnel_csum", VirtIONet, host_features_ex,
>> +                        VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM, true),
>>  };
> 
> Need compatibility work like:
> 
> d83f46d189 ("virtio-pci: compat page aligned ATS")

If I read correctly the only missing pieces are the hw_compat_10_1
entries, am I correct?

If so, as mentioned here:

https://lists.gnu.org/archive/html/qemu-devel/2025-07/msg05032.html

I'll add the needed entries after that the hw_compat_10_1 will be created.

Thanks,

Paolo