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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-990d10439absm628407241.5.2026.10.20.12.27.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 12:27:47 -0700 (PDT) Date: Tue, 20 Oct 2026 15:27:46 -0400 From: Willem de Bruijn To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Willem de Bruijn , Chris Arges , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Phil Sutter , Jason Wang , =?UTF-8?B?RXVnZW5pbyBQw6lyZXo=?= , Xuan Zhuo , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, virtualization@lists.linux.dev, Max Krasnyansky , Rusty Russell , Simon Horman Message-ID: In-Reply-To: References: Subject: Re: [PATCH net v3 1/8] net: account for ingress-resolved virtio net hdr state X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Michael S. Tsirkin wrote: > The following patch will add ingress resolution of uncommon virtio net > hdr checksum metadata (software checksum completion at ingress) which > adds performance overhead to the packet processing. > > We should make it visible, so a hypothetical workload relying on > uncommon metadata can be distinguished from none at all. This way issues > in the parsing will be reported and not quietly pay the host-CPU > checksum overhead instead of offload. > > Flip every call to virtio_net_hdr_to_skb to test for negative errno > only, and have tun count these events per device as rx_csum_sw, exposed > via ethtool -S. > > Assisted-by: LLM > Signed-off-by: Michael S. Tsirkin > --- > drivers/net/tap.c | 4 ++-- > drivers/net/tun.c | 41 ++++++++++++++++++++++++++++++++++++++-- > drivers/net/virtio_net.c | 2 +- > net/packet/af_packet.c | 4 ++-- > 4 files changed, 44 insertions(+), 7 deletions(-) > > diff --git a/drivers/net/tap.c b/drivers/net/tap.c > index ff67d99deb39..73e883394446 100644 > --- a/drivers/net/tap.c > +++ b/drivers/net/tap.c > @@ -649,7 +649,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control, > > if (vnet_hdr_len) { > err = tun_vnet_hdr_to_skb(q->flags, skb, &vnet_hdr); > - if (err) { > + if (err < 0) { > rcu_read_unlock(); > drop_reason = SKB_DROP_REASON_DEV_HDR; > goto err_kfree; > @@ -1084,7 +1084,7 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp) > > if (vnet_hdr_len) { > err = tun_vnet_hdr_to_skb(q->flags, skb, gso); > - if (err) { > + if (err < 0) { > rcu_read_unlock(); > goto err_kfree; > } similar to tun, should tap count this event? > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 242899f7fd07..19cb443c89b0 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -210,6 +210,7 @@ struct tun_struct { > u32 flow_count; > u32 rx_batched; > atomic_long_t rx_frame_errors; > + atomic64_t rx_csum_sw; is a normal (and cheaper on 32b platforms) atomic_t or atomic_long_t sufficient? > struct bpf_prog __rcu *xdp_prog; > struct tun_prog __rcu *steering_prog; > struct tun_prog __rcu *filter_prog; > @@ -1935,11 +1936,16 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > break; > } > > - if (tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, &hdr)) { > + err = tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, &hdr); > + if (err < 0) { > atomic_long_inc(&tun->rx_frame_errors); > err = -EINVAL; > goto free_skb; > } > + if (err > 0) { } else if (err > 0) { > + atomic64_inc(&tun->rx_csum_sw); > + err = 0; > + } > > if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) > skb->protocol = eth_type_trans(skb, tun->dev); > @@ -2605,12 +2611,15 @@ static int tun_xdp_one(struct tun_struct *tun, > tnl_hdr = (struct virtio_net_hdr_v1_hash_tunnel *)gso; > skb->dev = tun->dev; > skb_set_network_header(skb, ETH_HLEN); > - if (tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, tnl_hdr)) { > + ret = tun_vnet_hdr_tnl_to_skb(tun->flags, features, skb, tnl_hdr); > + if (ret < 0) { > atomic_long_inc(&tun->rx_frame_errors); > kfree_skb(skb); > ret = -EINVAL; > goto out; > } > + if (ret > 0) same > + atomic64_inc(&tun->rx_csum_sw); maybe reset ret = 0 in all these branches > > skb->protocol = eth_type_trans(skb, tun->dev); > skb_reset_network_header(skb); > @@ -3739,7 +3748,35 @@ static void tun_get_channels(struct net_device *dev, > channels->max_combined = tun->flags & IFF_MULTI_QUEUE ? MAX_TAP_QUEUES : 1; > } > > +#define TUN_STATS_LEN 1 > +static const char tun_ethtool_strings[TUN_STATS_LEN][ETH_GSTRING_LEN] = { > + "rx_csum_sw", > +}; > + > +static int tun_get_sset_count(struct net_device *dev, int sset) > +{ > + return sset == ETH_SS_STATS ? TUN_STATS_LEN : -EOPNOTSUPP; > +} > + > +static void tun_get_strings(struct net_device *dev, u32 stringset, u8 *data) > +{ > + if (stringset == ETH_SS_STATS) > + memcpy(data, tun_ethtool_strings, > + sizeof(tun_ethtool_strings)); > +} > + > +static void tun_get_ethtool_stats(struct net_device *dev, > + struct ethtool_stats *stats, u64 *data) > +{ > + struct tun_struct *tun = netdev_priv(dev); > + > + data[0] = atomic64_read(&tun->rx_csum_sw); > +} > + > static const struct ethtool_ops tun_ethtool_ops = { > + .get_sset_count = tun_get_sset_count, > + .get_strings = tun_get_strings, > + .get_ethtool_stats = tun_get_ethtool_stats, > .supported_coalesce_params = ETHTOOL_COALESCE_RX_MAX_FRAMES, > .get_drvinfo = tun_get_drvinfo, > .get_msglevel = tun_get_msglevel, > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index daab43ac92ce..2e6fd81df9c4 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2519,7 +2519,7 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue * > skb_set_network_header(skb, ETH_HLEN); > if (virtio_net_hdr_tnl_to_skb(skb, &hdr->tnl_hdr, vi->rx_tnl, > vi->rx_tnl_csum, > - virtio_is_little_endian(vi->vdev))) { > + virtio_is_little_endian(vi->vdev)) < 0) { > net_warn_ratelimited("%s: bad gso: type: %x, size: %u, flags %x tunnel %d tnl csum %d\n", > dev->name, hdr->hdr.gso_type, > hdr->hdr.gso_size, hdr->hdr.flags, should virtio_net count these too? Or do we assume that devices are more trustworthy, so unlikely to cause this issue? > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 52ae3d875e97..e6aec9ecfa99 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2913,7 +2913,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > } > > if (has_vnet_hdr) { > - if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le())) { > + if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le()) < 0) { > tp_len = -EINVAL; > goto tpacket_error; > } > @@ -3136,7 +3136,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) > > if (vnet_hdr_sz) { > err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le()); > - if (err) > + if (err < 0) > goto out_free; > len += vnet_hdr_sz; > } > -- > MST >