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Wed, 21 Oct 2026 09:28:40 -0700 (PDT) X-Received: by 2002:adf:f5c2:0:b0:48d:ed3c:4cdd with SMTP id ffacd0b85a97d-48e264e014cmr4386659f8f.49.1792600119920; Wed, 21 Oct 2026 09:28:39 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:1536:fc00:b838:383:1c7:6e81]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e25835b1dsm7086866f8f.40.2026.10.21.09.28.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 09:28:38 -0700 (PDT) Date: Wed, 21 Oct 2026 12:28:35 -0400 From: "Michael S. Tsirkin" To: Willem de Bruijn Cc: linux-kernel@vger.kernel.org, Chris Arges , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Phil Sutter , Jason Wang , Eugenio =?iso-8859-1?Q?P=E9rez?= , 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 , Richard Weinberger , Anton Ivanov , Johannes Berg , Simon Horman , linux-um@lists.infradead.org Subject: Re: [PATCH net v4 1/7] net: account for ingress-resolved virtio net hdr state Message-ID: <20261021122818-mutt-send-email-mst@kernel.org> References: 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-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Oct 21, 2026 at 12:08:06PM -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. The um vector raw transport even ignored the return value > > altogether: rejected packets went on into the stack with their > > metadata unvalidated, so check it there as well. > > > > Have tun, tap and virtio_net count these events per device as > > rx_csum_sw, exposed via ethtool -S. > > > > Signed-off-by: Michael S. Tsirkin > > --- > > arch/um/drivers/vector_transports.c | 4 ++- > > drivers/net/ipvlan/ipvtap.c | 36 +++++++++++++++++++++++++ > > drivers/net/macvtap.c | 36 +++++++++++++++++++++++++ > > drivers/net/tap.c | 8 ++++-- > > drivers/net/tun.c | 41 +++++++++++++++++++++++++++-- > > drivers/net/virtio_net.c | 15 ++++++++--- > > include/linux/if_tap.h | 1 + > > net/packet/af_packet.c | 4 +-- > > 8 files changed, 135 insertions(+), 10 deletions(-) > > > > diff --git a/arch/um/drivers/vector_transports.c b/arch/um/drivers/vector_transports.c > > index e1fb2a76fdff..8b7548458663 100644 > > --- a/arch/um/drivers/vector_transports.c > > +++ b/arch/um/drivers/vector_transports.c > > @@ -210,7 +210,9 @@ static int raw_verify_header( > > return 1; > > > > skb_set_network_header(skb, ETH_HLEN); > > - virtio_net_hdr_to_skb(skb, vheader, virtio_legacy_is_little_endian()); > > + if (virtio_net_hdr_to_skb(skb, vheader, > > + virtio_legacy_is_little_endian()) < 0) > > + return -1; > > return 0; > > } > > > > diff --git a/drivers/net/ipvlan/ipvtap.c b/drivers/net/ipvlan/ipvtap.c > > index 66c949d94261..9e2f1c7073d2 100644 > > --- a/drivers/net/ipvlan/ipvtap.c > > +++ b/drivers/net/ipvlan/ipvtap.c > > @@ -1,5 +1,6 @@ > > // SPDX-License-Identifier: GPL-2.0-only > > #include > > +#include > > #include "ipvlan.h" > > #include > > #include > > @@ -74,6 +75,32 @@ static void ipvtap_update_features(struct tap_dev *tap, > > netdev_update_features(vlan->dev); > > } > > > > +static int ipvtap_get_sset_count(struct net_device *dev, int sset) > > +{ > > + return sset == ETH_SS_STATS ? 1 : -EOPNOTSUPP; > > +} > > + > > +static void ipvtap_get_strings(struct net_device *dev, u32 stringset, > > + u8 *data) > > +{ > > + if (stringset == ETH_SS_STATS) > > + ethtool_puts(&data, "rx_csum_sw"); > > +} > > + > > +static void ipvtap_get_ethtool_stats(struct net_device *dev, > > + struct ethtool_stats *stats, > > + u64 *data) > > +{ > > + struct ipvtap_dev *vlantap = netdev_priv(dev); > > + > > + data[0] = atomic64_read(&vlantap->tap.rx_csum_sw); > > +} > > + > > +/* checkpatch warns but this can't be const: cloned from ipvlan's > > + * ops at newlink time, with the statistics above added. > > + */ > > +static struct ethtool_ops ipvtap_ethtool_ops; > > + > > static int ipvtap_newlink(struct net_device *dev, > > struct rtnl_newlink_params *params, > > struct netlink_ext_ack *extack) > > @@ -91,6 +118,15 @@ static int ipvtap_newlink(struct net_device *dev, > > vlantap->tap.update_features = ipvtap_update_features; > > vlantap->tap.count_rx_dropped = ipvtap_count_rx_dropped; > > > > + /* ipvlan's ethtool ops are already installed at this point; > > + * clone them and add the tap statistics on top. > > + */ > > + ipvtap_ethtool_ops = *dev->ethtool_ops; > > + ipvtap_ethtool_ops.get_sset_count = ipvtap_get_sset_count; > > + ipvtap_ethtool_ops.get_strings = ipvtap_get_strings; > > + ipvtap_ethtool_ops.get_ethtool_stats = ipvtap_get_ethtool_stats; > > + dev->ethtool_ops = &ipvtap_ethtool_ops; > > + > > LLM: > > This cloning pattern in ipvtap_newlink (and identically in macvtap_newlink below) has serious concurrency and hardening issues: > 1. Concurrent Data Race: ipvtap_ethtool_ops is a single static global struct. Although newlink runs under rtnl_lock(), ethtool readers on > existing devices (e.g. netlink stats_prepare_data() and strset_prepare_data()) run under rcu_read_lock() without RTNL. Whenever a new > ipvtap/macvtap device is created, ipvtap_ethtool_ops = *dev->ethtool_ops overwrites the global ops table in-place, temporarily clearing > get_sset_count and get_strings to NULL before re-populating them. Any concurrent ethtool query on an existing device can observe NULL or > torn function pointers. > 2. Writable Function Pointer Table: ethtool_ops contains function pointers and should reside in .rodata (const) to prevent kernel exploit > targets. > 3. Hardcoded Set Count: ipvtap_get_sset_count returns 1 unconditionally; if the lower device ever adds ethtool stats in the future, they > are completely masked. > > Instead of dynamically mutating a non-const global ops struct on every newlink, either: > • Export the base ops from macvlan/ipvlan so tap can declare a const struct ethtool_ops directly, or > • At the very least, initialize it once (e.g. guarded by a check or at module init) so it is not re-clobbered while readers are active. > > Additionally, in general, ipvlan/macvlan/tun/tap changes are preferred > to be individual patches. > > I don't think this is as important as the main patches 4 and 5. If you > want to submit quickly, I would drop/postpone these second order > features. Maybe go back to the previous tun-only counter for now, if > you consider that important enough. ok I will do tun only. > > err = netdev_rx_handler_register(dev, tap_handle_frame, &vlantap->tap); > > if (err) > > return err; > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > > index cc975dfb7380..3288cc6ae6c2 100644 > > --- a/drivers/net/macvtap.c > > +++ b/drivers/net/macvtap.c > > @@ -1,5 +1,6 @@ > > // SPDX-License-Identifier: GPL-2.0-only > > #include > > +#include > > #include > > #include > > #include > > @@ -78,6 +79,32 @@ static void macvtap_update_features(struct tap_dev *tap, > > netdev_update_features(vlan->dev); > > } > > > > +static int macvtap_get_sset_count(struct net_device *dev, int sset) > > +{ > > + return sset == ETH_SS_STATS ? 1 : -EOPNOTSUPP; > > +} > > + > > +static void macvtap_get_strings(struct net_device *dev, u32 stringset, > > + u8 *data) > > +{ > > + if (stringset == ETH_SS_STATS) > > + ethtool_puts(&data, "rx_csum_sw"); > > +} > > + > > +static void macvtap_get_ethtool_stats(struct net_device *dev, > > + struct ethtool_stats *stats, > > + u64 *data) > > +{ > > + struct macvtap_dev *vlantap = netdev_priv(dev); > > + > > + data[0] = atomic64_read(&vlantap->tap.rx_csum_sw); > > +} > > + > > +/* checkpatch warns but this can't be const: cloned from macvlan's > > + * ops at newlink time, with the statistics above added. > > + */ > > +static struct ethtool_ops macvtap_ethtool_ops; > > + > > static int macvtap_newlink(struct net_device *dev, > > struct rtnl_newlink_params *params, > > struct netlink_ext_ack *extack) > > @@ -99,6 +126,15 @@ static int macvtap_newlink(struct net_device *dev, > > vlantap->tap.count_rx_dropped = macvtap_count_rx_dropped; > > vlantap->tap.update_features = macvtap_update_features; > > > > + /* macvlan's ethtool ops are already installed at this point; > > + * clone them and add the tap statistics on top. > > + */ > > + macvtap_ethtool_ops = *dev->ethtool_ops; > > + macvtap_ethtool_ops.get_sset_count = macvtap_get_sset_count; > > + macvtap_ethtool_ops.get_strings = macvtap_get_strings; > > + macvtap_ethtool_ops.get_ethtool_stats = macvtap_get_ethtool_stats; > > + dev->ethtool_ops = &macvtap_ethtool_ops; > > + > > err = netdev_rx_handler_register(dev, tap_handle_frame, &vlantap->tap); > > if (err) > > return err; > > diff --git a/drivers/net/tap.c b/drivers/net/tap.c > > index ff67d99deb39..d7520622e809 100644 > > --- a/drivers/net/tap.c > > +++ b/drivers/net/tap.c > > @@ -649,11 +649,13 @@ 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; > > } > > + if (err > 0) > > + atomic64_inc(&tap->rx_csum_sw); > > } > > > > skb_probe_transport_header(skb); > > @@ -1084,10 +1086,12 @@ 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; > > } > > + if (err > 0) > > + atomic64_inc(&tap->rx_csum_sw); > > (repeat) reset err to 0 in all paths. > > > } > > > > skb_probe_transport_header(skb); > > 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; > > 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) { > > + 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) > > + atomic64_inc(&tun->rx_csum_sw); > > > > 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..b0441bf8e875 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -125,6 +125,7 @@ struct virtnet_rq_stats { > > u64_stats_t packets; > > u64_stats_t bytes; > > u64_stats_t drops; > > + u64_stats_t rx_csum_sw; > > u64_stats_t xdp_packets; > > u64_stats_t xdp_tx; > > u64_stats_t xdp_redirects; > > @@ -158,6 +159,7 @@ static const struct virtnet_stat_desc virtnet_sq_stats_desc[] = { > > > > static const struct virtnet_stat_desc virtnet_rq_stats_desc[] = { > > VIRTNET_RQ_STAT("drops", drops), > > + VIRTNET_RQ_STAT("rx_csum_sw", rx_csum_sw), > > VIRTNET_RQ_STAT("xdp_packets", xdp_packets), > > VIRTNET_RQ_STAT("xdp_tx", xdp_tx), > > VIRTNET_RQ_STAT("xdp_redirects", xdp_redirects), > > @@ -2502,6 +2504,7 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue * > > { > > struct virtio_net_common_hdr *hdr; > > struct net_device *dev = vi->dev; > > + int ret; > > > > hdr = skb_vnet_common_hdr(skb); > > if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report) > > @@ -2517,15 +2520,21 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue * > > > > skb->dev = dev; > > 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))) { > > + ret = virtio_net_hdr_tnl_to_skb(skb, &hdr->tnl_hdr, vi->rx_tnl, > > + vi->rx_tnl_csum, > > + virtio_is_little_endian(vi->vdev)); > > + if (ret < 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, > > vi->rx_tnl, vi->rx_tnl_csum); > > goto frame_err; > > } > > + if (ret > 0) { > > + u64_stats_update_begin(&rq->stats.syncp); > > + u64_stats_inc(&rq->stats.rx_csum_sw); > > + u64_stats_update_end(&rq->stats.syncp); > > + } > > Because rx_csum_sw was added to virtnet_rq_stats_desc[], virtnet_poll() already iterates through virtnet_rq_stats_desc[] and syncs each > field from the local stack stats into rq->stats at the end of the NAPI polling cycle inside a single u64_stats_update_begin/end(&rq- > >stats.syncp). > Calling u64_stats_update_begin/end(&rq->stats.syncp) directly per-packet in virtnet_receive_done() bypasses that batching pattern. While SW > csum is off the fast path, it is inconsistent with how other rq stats are handled. > > > > > skb_record_rx_queue(skb, vq2rxq(rq->vq)); > > skb->protocol = eth_type_trans(skb, dev); > > diff --git a/include/linux/if_tap.h b/include/linux/if_tap.h > > index 553552fa635c..4eac24bb1df7 100644 > > --- a/include/linux/if_tap.h > > +++ b/include/linux/if_tap.h > > @@ -41,6 +41,7 @@ struct tap_dev { > > struct list_head queue_list; > > int numvtaps; > > int numqueues; > > + atomic64_t rx_csum_sw; > > netdev_features_t tap_features; > > int minor; > > > > 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 > > >