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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id ada2fe7eead31-7cc9236f63csm306154137.5.2026.10.20.13.02.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 13:02:26 -0700 (PDT) Date: Tue, 20 Oct 2026 16:02:26 -0400 From: Willem de Bruijn To: "Michael S. Tsirkin" , Willem de Bruijn Cc: linux-kernel@vger.kernel.org, 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: <20261020153650-mutt-send-email-mst@kernel.org> References: <20261020153650-mutt-send-email-mst@kernel.org> Subject: Re: [PATCH net v3 1/8] net: account for ingress-resolved virtio net hdr state X-Mailing-List: linux-kernel@vger.kernel.org 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: > On Tue, Oct 20, 2026 at 03:27:46PM -0400, Willem de Bruijn wrote: > > 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? > > well it can overflow easily. i don't know that we care that a slow > path will be even a bit slower on these ancient platforms. correct > reporting seems more important. Ok. I would hope that monitoring catches this before it hits 4B, but agreed that as slow path it doesn't matter. > > > > 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? > > With memory encryption, from an untrusted host? > i can add that. I honestly don't know if it's worth the effort. Just curious whether you had purposely skipped this and tap. > > > > 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 > > > > > >