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Message-ID: <CACGkMEv5cXoA7aPOUmE63fRg21Kefx3MNE4VenGciL92WbvS_g@mail.gmail.com>
Date: Mon, 26 May 2025 12:40:44 +0800
From: Jason Wang <jasowang@...hat.com>
To: Paolo Abeni <pabeni@...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>
Subject: Re: [PATCH net-next 7/8] tun: enable gso over UDP tunnel support.
On Wed, May 21, 2025 at 6:34 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> Add new tun features to represent the newly introduced virtio
> GSO over UDP tunnel offload. Allows detection and selection of
> such features via the existing TUNSETOFFLOAD ioctl, store the
> tunnel offload configuration in the highest bit of the tun flags
> and compute the expected virtio header size and tunnel header
> offset using such bits, so that we can plug almost seamless the
> the newly introduced virtio helpers to serialize the extended
> virtio header.
>
> As the tun features and the virtio hdr size are configured
> separately, the data path need to cope with (hopefully transient)
> inconsistent values.
I'm not sure it's a good idea to deal with this inconsistency in this
series as it is not specific to tunnel offloading. It could be a
dependency for this patch or we can leave it for the future and just
to make sure mis-configuration won't cause any kernel issues.
>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> drivers/net/tun.c | 77 ++++++++++++++++++++++++++++++++-----
> drivers/net/tun_vnet.h | 74 ++++++++++++++++++++++++++++-------
> include/uapi/linux/if_tun.h | 9 +++++
> 3 files changed, 137 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7babd1e9a378b..ef8cef48b66f5 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -186,7 +186,8 @@ struct tun_struct {
> struct net_device *dev;
> netdev_features_t set_features;
> #define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
> - NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4)
> + NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4 | \
> + NETIF_F_GSO_UDP_TUNNEL | NETIF_F_GSO_UDP_TUNNEL_CSUM)
>
> int align;
> int vnet_hdr_sz;
> @@ -925,6 +926,7 @@ static int tun_net_init(struct net_device *dev)
> dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
> TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
> NETIF_F_HW_VLAN_STAG_TX;
> + dev->hw_enc_features = dev->hw_features;
> dev->features = dev->hw_features;
> dev->vlan_features = dev->features &
> ~(NETIF_F_HW_VLAN_CTAG_TX |
> @@ -1698,7 +1700,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> struct sk_buff *skb;
> size_t total_len = iov_iter_count(from);
> size_t len = total_len, align = tun->align, linear;
> - struct virtio_net_hdr gso = { 0 };
> + char buf[TUN_VNET_TNL_SIZE];
I wonder why not simply
1) define the structure virtio_net_hdr_tnl_gso and use that
or
2) stick the gso here and use iter advance to get
virtio_net_hdr_tunnel when necessary?
> + struct virtio_net_hdr *gso;
> int good_linear;
> int copylen;
> int hdr_len = 0;
> @@ -1708,6 +1711,15 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> int skb_xdp = 1;
> bool frags = tun_napi_frags_enabled(tfile);
> enum skb_drop_reason drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
> + unsigned int flags = tun->flags & ~TUN_VNET_TNL_MASK;
> +
> + /*
> + * Keep it easy and always zero the whole buffer, even if the
> + * tunnel-related field will be touched only when the feature
> + * is enabled and the hdr size id compatible.
> + */
> + memset(buf, 0, sizeof(buf));
> + gso = (void *)buf;
>
> if (!(tun->flags & IFF_NO_PI)) {
> if (len < sizeof(pi))
> @@ -1720,8 +1732,16 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>
> if (tun->flags & IFF_VNET_HDR) {
> int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
> + int parsed_size;
>
> - hdr_len = tun_vnet_hdr_get(vnet_hdr_sz, tun->flags, from, &gso);
> + if (vnet_hdr_sz < TUN_VNET_TNL_SIZE) {
> + parsed_size = vnet_hdr_sz;
> + } else {
> + parsed_size = TUN_VNET_TNL_SIZE;
> + flags |= TUN_VNET_TNL_MASK;
> + }
> + hdr_len = __tun_vnet_hdr_get(vnet_hdr_sz, parsed_size,
> + flags, from, gso);
> if (hdr_len < 0)
> return hdr_len;
>
> @@ -1755,7 +1775,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> * (e.g gso or jumbo packet), we will do it at after
> * skb was created with generic XDP routine.
> */
> - skb = tun_build_skb(tun, tfile, from, &gso, len, &skb_xdp);
> + skb = tun_build_skb(tun, tfile, from, gso, len, &skb_xdp);
> err = PTR_ERR_OR_ZERO(skb);
> if (err)
> goto drop;
> @@ -1799,7 +1819,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> }
> }
>
> - if (tun_vnet_hdr_to_skb(tun->flags, skb, &gso)) {
> + if (tun_vnet_hdr_to_skb(flags, skb, gso)) {
> atomic_long_inc(&tun->rx_frame_errors);
> err = -EINVAL;
> goto free_skb;
> @@ -2050,13 +2070,26 @@ static ssize_t tun_put_user(struct tun_struct *tun,
> }
>
> if (vnet_hdr_sz) {
> - struct virtio_net_hdr gso;
> + char buf[TUN_VNET_TNL_SIZE];
> + struct virtio_net_hdr *gso;
> + int flags = tun->flags;
> + int parsed_size;
> +
> + gso = (void *)buf;
> + parsed_size = tun_vnet_parse_size(tun->flags);
> + if (unlikely(vnet_hdr_sz < parsed_size)) {
> + /* Inconsistent hdr size and (tunnel) offloads:
> + * strips the latter
> + */
> + flags &= ~TUN_VNET_TNL_MASK;
> + parsed_size = sizeof(struct virtio_net_hdr);
> + };
>
> - ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
> + ret = tun_vnet_hdr_from_skb(flags, tun->dev, skb, gso);
> if (ret)
> return ret;
>
> - ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
> + ret = __tun_vnet_hdr_put(vnet_hdr_sz, parsed_size, iter, gso);
> if (ret)
> return ret;
> }
> @@ -2366,6 +2399,7 @@ static int tun_xdp_one(struct tun_struct *tun,
> int metasize = 0;
> int ret = 0;
> bool skb_xdp = false;
> + unsigned int flags;
> struct page *page;
>
> if (unlikely(datasize < ETH_HLEN))
> @@ -2426,7 +2460,16 @@ static int tun_xdp_one(struct tun_struct *tun,
> if (metasize > 0)
> skb_metadata_set(skb, metasize);
>
> - if (tun_vnet_hdr_to_skb(tun->flags, skb, gso)) {
> + /* Assume tun offloads are enabled if the provided hdr is large
> + * enough.
> + */
> + if (READ_ONCE(tun->vnet_hdr_sz) >= TUN_VNET_TNL_SIZE &&
> + xdp->data - xdp->data_hard_start >= TUN_VNET_TNL_SIZE)
> + flags = tun->flags | TUN_VNET_TNL_MASK;
> + else
> + flags = tun->flags & ~TUN_VNET_TNL_MASK;
> +
> + if (tun_vnet_hdr_to_skb(flags, skb, gso)) {
> atomic_long_inc(&tun->rx_frame_errors);
> kfree_skb(skb);
> ret = -EINVAL;
> @@ -2812,6 +2855,8 @@ static void tun_get_iff(struct tun_struct *tun, struct ifreq *ifr)
>
> }
>
> +#define PLAIN_GSO (NETIF_F_GSO_UDP_L4 | NETIF_F_TSO | NETIF_F_TSO6)
> +
> /* This is like a cut-down ethtool ops, except done via tun fd so no
> * privs required. */
> static int set_offload(struct tun_struct *tun, unsigned long arg)
> @@ -2841,6 +2886,17 @@ static int set_offload(struct tun_struct *tun, unsigned long arg)
> features |= NETIF_F_GSO_UDP_L4;
> arg &= ~(TUN_F_USO4 | TUN_F_USO6);
> }
> +
> + /* Tunnel offload is allowed only if some plain offload is
> + * available, too.
> + */
> + if (features & PLAIN_GSO && arg & TUN_F_UDP_TUNNEL_GSO) {
> + features |= NETIF_F_GSO_UDP_TUNNEL;
> + if (arg & TUN_F_UDP_TUNNEL_GSO_CSUM)
> + features |= NETIF_F_GSO_UDP_TUNNEL_CSUM;
> + arg &= ~(TUN_F_UDP_TUNNEL_GSO |
> + TUN_F_UDP_TUNNEL_GSO_CSUM);
> + }
> }
>
> /* This gives the user a way to test for new features in future by
> @@ -2852,7 +2908,8 @@ static int set_offload(struct tun_struct *tun, unsigned long arg)
> tun->dev->wanted_features &= ~TUN_USER_FEATURES;
> tun->dev->wanted_features |= features;
> netdev_update_features(tun->dev);
> -
> + tun_set_vnet_tnl(&tun->flags, !!(features & NETIF_F_GSO_UDP_TUNNEL),
> + !!(features & NETIF_F_GSO_UDP_TUNNEL_CSUM));
> return 0;
> }
>
> diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
> index 58b9ac7a5fc40..ab2d4396941ca 100644
> --- a/drivers/net/tun_vnet.h
> +++ b/drivers/net/tun_vnet.h
> @@ -5,6 +5,12 @@
> /* High bits in flags field are unused. */
> #define TUN_VNET_LE 0x80000000
> #define TUN_VNET_BE 0x40000000
> +#define TUN_VNET_TNL 0x20000000
> +#define TUN_VNET_TNL_CSUM 0x10000000
> +#define TUN_VNET_TNL_MASK (TUN_VNET_TNL | TUN_VNET_TNL_CSUM)
> +
> +#define TUN_VNET_TNL_SIZE (sizeof(struct virtio_net_hdr_v1) + \
Should this be virtio_net_hdr_v1_hash?
> + sizeof(struct virtio_net_hdr_tunnel))
>
> static inline bool tun_vnet_legacy_is_little_endian(unsigned int flags)
> {
> @@ -45,6 +51,13 @@ static inline long tun_set_vnet_be(unsigned int *flags, int __user *argp)
> return 0;
> }
>
> +static inline void tun_set_vnet_tnl(unsigned int *flags, bool tnl, bool tnl_csum)
> +{
> + *flags = (*flags & ~TUN_VNET_TNL_MASK) |
> + tnl * TUN_VNET_TNL |
> + tnl_csum * TUN_VNET_TNL_CSUM;
We could refer to netdev via tun_struct, so I don't understand why we
need to duplicate the features in tun->flags (we don't do that for
other GSO/CSUM stuffs).
> +}
> +
> static inline bool tun_vnet_is_little_endian(unsigned int flags)
> {
> return flags & TUN_VNET_LE || tun_vnet_legacy_is_little_endian(flags);
> @@ -107,16 +120,33 @@ static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
> }
> }
>
> -static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
> - struct iov_iter *from,
> - struct virtio_net_hdr *hdr)
> +static inline unsigned int tun_vnet_parse_size(unsigned int flags)
> +{
> + if (!(flags & TUN_VNET_TNL))
> + return sizeof(struct virtio_net_hdr);
> +
> + return TUN_VNET_TNL_SIZE;
> +}
> +
> +static inline unsigned int tun_vnet_tnl_offset(unsigned int flags)
> +{
> + if (!(flags & TUN_VNET_TNL))
> + return 0;
> +
> + return sizeof(struct virtio_net_hdr_v1);
> +}
> +
> +static inline int __tun_vnet_hdr_get(int sz, int parsed_size,
> + unsigned int flags,
> + struct iov_iter *from,
> + struct virtio_net_hdr *hdr)
> {
> u16 hdr_len;
>
> if (iov_iter_count(from) < sz)
> return -EINVAL;
>
> - if (!copy_from_iter_full(hdr, sizeof(*hdr), from))
> + if (!copy_from_iter_full(hdr, parsed_size, from))
> return -EFAULT;
>
> hdr_len = tun_vnet16_to_cpu(flags, hdr->hdr_len);
> @@ -129,30 +159,47 @@ static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
> if (hdr_len > iov_iter_count(from))
> return -EINVAL;
>
> - iov_iter_advance(from, sz - sizeof(*hdr));
> + iov_iter_advance(from, sz - parsed_size);
>
> return hdr_len;
> }
>
> -static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
> - const struct virtio_net_hdr *hdr)
> +static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
> + struct iov_iter *from,
> + struct virtio_net_hdr *hdr)
> +{
> + return __tun_vnet_hdr_get(sz, sizeof(*hdr), flags, from, hdr);
> +}
> +
> +static inline int __tun_vnet_hdr_put(int sz, int parsed_size,
> + struct iov_iter *iter,
> + const struct virtio_net_hdr *hdr)
> {
> if (unlikely(iov_iter_count(iter) < sz))
> return -EINVAL;
>
> - if (unlikely(copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr)))
> + if (unlikely(copy_to_iter(hdr, parsed_size, iter) != parsed_size))
> return -EFAULT;
>
> - if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr))
> + if (iov_iter_zero(sz - parsed_size, iter) != sz - parsed_size)
> return -EFAULT;
>
> return 0;
> }
>
> +static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
> + const struct virtio_net_hdr *hdr)
> +{
> + return __tun_vnet_hdr_put(sz, sizeof(*hdr), iter, hdr);
> +}
> +
> static inline int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
> const struct virtio_net_hdr *hdr)
> {
> - return virtio_net_hdr_to_skb(skb, hdr, tun_vnet_is_little_endian(flags));
> + return virtio_net_hdr_tnl_to_skb(skb, hdr,
> + tun_vnet_tnl_offset(flags),
> + !!(flags & TUN_VNET_TNL_CSUM),
> + tun_vnet_is_little_endian(flags));
> }
>
> static inline int tun_vnet_hdr_from_skb(unsigned int flags,
> @@ -161,10 +208,11 @@ static inline int tun_vnet_hdr_from_skb(unsigned int flags,
> struct virtio_net_hdr *hdr)
> {
> int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
> + int tnl_offset = tun_vnet_tnl_offset(flags);
>
> - if (virtio_net_hdr_from_skb(skb, hdr,
> - tun_vnet_is_little_endian(flags), true,
> - vlan_hlen)) {
> + if (virtio_net_hdr_tnl_from_skb(skb, hdr, tnl_offset,
> + tun_vnet_is_little_endian(flags),
> + vlan_hlen)) {
> struct skb_shared_info *sinfo = skb_shinfo(skb);
>
> if (net_ratelimit()) {
> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index 287cdc81c9390..a25a5e7a08ffa 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -93,6 +93,15 @@
> #define TUN_F_USO4 0x20 /* I can handle USO for IPv4 packets */
> #define TUN_F_USO6 0x40 /* I can handle USO for IPv6 packets */
>
> +#define TUN_F_UDP_TUNNEL_GSO 0x080 /* I can handle TSO/USO for UDP
> + * tunneled packets
> + */
> +#define TUN_F_UDP_TUNNEL_GSO_CSUM 0x100 /* I can handle TSO/USO for UDP
> + * tunneled packets requiring
> + * csum offload for the outer
> + * header
> + */
> +
> /* Protocol info prepended to the packets (when IFF_NO_PI is not set) */
> #define TUN_PKT_STRIP 0x0001
> struct tun_pi {
> --
> 2.49.0
>
Thanks
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