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Date:   Thu, 21 May 2020 11:55:24 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>, dsahern@...il.com,
        davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...lanox.com, idosch@...lanox.com,
        petrm@...lanox.com
Subject: Re: [PATCH net-next v2 2/5] vxlan: ecmp support for mac fdb entries

On 20/05/2020 07:33, Roopa Prabhu wrote:
> From: Roopa Prabhu <roopa@...ulusnetworks.com>
> 
> Todays vxlan mac fdb entries can point to multiple remote
> ips (rdsts) with the sole purpose of replicating
> broadcast-multicast and unknown unicast packets to those remote ips.
> 
> E-VPN multihoming [1,2,3] requires bridged vxlan traffic to be
> load balanced to remote switches (vteps) belonging to the
> same multi-homed ethernet segment (E-VPN multihoming is analogous
> to multi-homed LAG implementations, but with the inter-switch
> peerlink replaced with a vxlan tunnel). In other words it needs
> support for mac ecmp. Furthermore, for faster convergence, E-VPN
> multihoming needs the ability to update fdb ecmp nexthops independent
> of the fdb entries.
> 
> New route nexthop API is perfect for this usecase.
> This patch extends the vxlan fdb code to take a nexthop id
> pointing to an ecmp nexthop group.
> 
> Changes include:
> - New NDA_NH_ID attribute for fdbs
> - Use the newly added fdb nexthop groups
> - makes vxlan rdsts and nexthop handling code mutually
>   exclusive
> - since this is a new use-case and the requirement is for ecmp
> nexthop groups, the fdb add and update path checks that the
> nexthop is really an ecmp nexthop group. This check can be relaxed
> in the future, if we want to introduce replication fdb nexthop groups
> and allow its use in lieu of current rdst lists.
> - fdb update requests with nexthop id's only allowed for existing
> fdb's that have nexthop id's
> - learning will not override an existing fdb entry with nexthop
> group
> - I have wrapped the switchdev offload code around the presence of
> rdst
> - I think there is scope for simplyfing vxlan_xmit_one: Will see
> what I can do before the non-RFC version
> 
> [1] E-VPN RFC https://tools.ietf.org/html/rfc7432
> [2] E-VPN with vxlan https://tools.ietf.org/html/rfc8365
> [3] http://vger.kernel.org/lpc_net2018_talks/scaling_bridge_fdb_database_slidesV3.pdf
> 
> Includes a null check fix in vxlan_xmit from Nikolay
> 
> v2 - Fixed build issue:
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Roopa Prabhu <roopa@...ulusnetworks.com>
> ---
>  drivers/net/vxlan.c            | 301 +++++++++++++++++++++++++++++++++--------
>  include/net/vxlan.h            |  25 ++++
>  include/uapi/linux/neighbour.h |   1 +
>  net/core/neighbour.c           |   2 +
>  4 files changed, 270 insertions(+), 59 deletions(-)
> 

Overall looks good, just one more potential issue with the xmit below.

> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index a5b415f..380d887 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -26,6 +26,7 @@
>  #include <net/netns/generic.h>
>  #include <net/tun_proto.h>
>  #include <net/vxlan.h>
> +#include <net/nexthop.h>
>  
>  #if IS_ENABLED(CONFIG_IPV6)
>  #include <net/ip6_tunnel.h>
> @@ -78,6 +79,8 @@ struct vxlan_fdb {
>  	u16		  state;	/* see ndm_state */
>  	__be32		  vni;
>  	u16		  flags;	/* see ndm_flags and below */
> +	struct list_head  nh_list;
> +	struct nexthop __rcu *nh;
>  };
>  
>  #define NTF_VXLAN_ADDED_BY_USER 0x100
> @@ -174,11 +177,15 @@ static inline struct hlist_head *vs_head(struct net *net, __be16 port)
>   */
>  static inline struct vxlan_rdst *first_remote_rcu(struct vxlan_fdb *fdb)
>  {
> +	if (rcu_access_pointer(fdb->nh))
> +		return NULL;
>  	return list_entry_rcu(fdb->remotes.next, struct vxlan_rdst, list);
>  }
>  
>  static inline struct vxlan_rdst *first_remote_rtnl(struct vxlan_fdb *fdb)
>  {
> +	if (rcu_access_pointer(fdb->nh))
> +		return NULL;
>  	return list_first_entry(&fdb->remotes, struct vxlan_rdst, list);
>  }
>  
> @@ -251,9 +258,10 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct vxlan_dev *vxlan,
>  {
>  	unsigned long now = jiffies;
>  	struct nda_cacheinfo ci;
> +	bool send_ip, send_eth;
>  	struct nlmsghdr *nlh;
> +	struct nexthop *nh;
>  	struct ndmsg *ndm;
> -	bool send_ip, send_eth;
>  
>  	nlh = nlmsg_put(skb, portid, seq, type, sizeof(*ndm), flags);
>  	if (nlh == NULL)
> @@ -264,16 +272,21 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct vxlan_dev *vxlan,
>  
>  	send_eth = send_ip = true;
>  
> +	nh = rcu_dereference_rtnl(fdb->nh);
>  	if (type == RTM_GETNEIGH) {
> -		send_ip = !vxlan_addr_any(&rdst->remote_ip);
> +		if (rdst) {
> +			send_ip = !vxlan_addr_any(&rdst->remote_ip);
> +			ndm->ndm_family = send_ip ? rdst->remote_ip.sa.sa_family : AF_INET;
> +		} else if (nh) {
> +			ndm->ndm_family = nexthop_get_family(nh);
> +		}
>  		send_eth = !is_zero_ether_addr(fdb->eth_addr);
> -		ndm->ndm_family = send_ip ? rdst->remote_ip.sa.sa_family : AF_INET;
>  	} else
>  		ndm->ndm_family	= AF_BRIDGE;
>  	ndm->ndm_state = fdb->state;
>  	ndm->ndm_ifindex = vxlan->dev->ifindex;
>  	ndm->ndm_flags = fdb->flags;
> -	if (rdst->offloaded)
> +	if (rdst && rdst->offloaded)
>  		ndm->ndm_flags |= NTF_OFFLOADED;
>  	ndm->ndm_type = RTN_UNICAST;
>  
> @@ -284,23 +297,30 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct vxlan_dev *vxlan,
>  
>  	if (send_eth && nla_put(skb, NDA_LLADDR, ETH_ALEN, &fdb->eth_addr))
>  		goto nla_put_failure;
> +	if (nh) {
> +		if (nla_put_u32(skb, NDA_NH_ID, nh->id))
> +			goto nla_put_failure;
> +	} else if (rdst) {
> +		if (send_ip && vxlan_nla_put_addr(skb, NDA_DST,
> +						  &rdst->remote_ip))
> +			goto nla_put_failure;
> +
> +		if (rdst->remote_port &&
> +		    rdst->remote_port != vxlan->cfg.dst_port &&
> +		    nla_put_be16(skb, NDA_PORT, rdst->remote_port))
> +			goto nla_put_failure;
> +		if (rdst->remote_vni != vxlan->default_dst.remote_vni &&
> +		    nla_put_u32(skb, NDA_VNI, be32_to_cpu(rdst->remote_vni)))
> +			goto nla_put_failure;
> +		if (rdst->remote_ifindex &&
> +		    nla_put_u32(skb, NDA_IFINDEX, rdst->remote_ifindex))
> +			goto nla_put_failure;
> +	}
>  
> -	if (send_ip && vxlan_nla_put_addr(skb, NDA_DST, &rdst->remote_ip))
> -		goto nla_put_failure;
> -
> -	if (rdst->remote_port && rdst->remote_port != vxlan->cfg.dst_port &&
> -	    nla_put_be16(skb, NDA_PORT, rdst->remote_port))
> -		goto nla_put_failure;
> -	if (rdst->remote_vni != vxlan->default_dst.remote_vni &&
> -	    nla_put_u32(skb, NDA_VNI, be32_to_cpu(rdst->remote_vni)))
> -		goto nla_put_failure;
>  	if ((vxlan->cfg.flags & VXLAN_F_COLLECT_METADATA) && fdb->vni &&
>  	    nla_put_u32(skb, NDA_SRC_VNI,
>  			be32_to_cpu(fdb->vni)))
>  		goto nla_put_failure;
> -	if (rdst->remote_ifindex &&
> -	    nla_put_u32(skb, NDA_IFINDEX, rdst->remote_ifindex))
> -		goto nla_put_failure;
>  
>  	ci.ndm_used	 = jiffies_to_clock_t(now - fdb->used);
>  	ci.ndm_confirmed = 0;
> @@ -401,7 +421,7 @@ static int vxlan_fdb_notify(struct vxlan_dev *vxlan, struct vxlan_fdb *fdb,
>  {
>  	int err;
>  
> -	if (swdev_notify) {
> +	if (swdev_notify && rd) {
>  		switch (type) {
>  		case RTM_NEWNEIGH:
>  			err = vxlan_fdb_switchdev_call_notifiers(vxlan, fdb, rd,
> @@ -805,6 +825,8 @@ static struct vxlan_fdb *vxlan_fdb_alloc(const u8 *mac, __u16 state,
>  	f->flags = ndm_flags;
>  	f->updated = f->used = jiffies;
>  	f->vni = src_vni;
> +	f->nh = NULL;
> +	INIT_LIST_HEAD(&f->nh_list);
>  	INIT_LIST_HEAD(&f->remotes);
>  	memcpy(f->eth_addr, mac, ETH_ALEN);
>  
> @@ -819,11 +841,78 @@ static void vxlan_fdb_insert(struct vxlan_dev *vxlan, const u8 *mac,
>  			   vxlan_fdb_head(vxlan, mac, src_vni));
>  }
>  
> +static int vxlan_fdb_nh_update(struct vxlan_dev *vxlan, struct vxlan_fdb *fdb,
> +			       u32 nhid, struct netlink_ext_ack *extack)
> +{
> +	struct nexthop *old_nh = rtnl_dereference(fdb->nh);
> +	struct nh_group *nhg;
> +	struct nexthop *nh;
> +	int err = -EINVAL;
> +
> +	if (old_nh && old_nh->id == nhid)
> +		return 0;
> +
> +	nh = nexthop_find_by_id(vxlan->net, nhid);
> +	if (!nh) {
> +		NL_SET_ERR_MSG(extack, "Nexthop id does not exist");
> +		goto err_inval;
> +	}
> +
> +	if (nh) {
> +		if (!nexthop_get(nh)) {
> +			NL_SET_ERR_MSG(extack, "Nexthop has been deleted");
> +			nh = NULL;
> +			goto err_inval;
> +		}
> +		if (!nh->is_fdb_nh) {
> +			NL_SET_ERR_MSG(extack, "Nexthop is not a fdb nexthop");
> +			goto err_inval;
> +		}
> +
> +		if (!nh->is_group || !nh->nh_grp->mpath) {
> +			NL_SET_ERR_MSG(extack, "Nexthop is not a multipath group");
> +			goto err_inval;
> +		}
> +
> +		/* check nexthop group family */
> +		nhg = rtnl_dereference(nh->nh_grp);
> +		switch (vxlan->default_dst.remote_ip.sa.sa_family) {
> +		case AF_INET:
> +			if (!nhg->has_v4) {
> +				err = -EAFNOSUPPORT;
> +				NL_SET_ERR_MSG(extack, "Nexthop group family not supported");
> +				goto err_inval;
> +			}
> +			break;
> +		case AF_INET6:
> +			if (nhg->has_v4) {
> +				err = -EAFNOSUPPORT;
> +				NL_SET_ERR_MSG(extack, "Nexthop group family not supported");
> +				goto err_inval;
> +			}
> +		}
> +	}
> +
> +	if (old_nh) {
> +		list_del_rcu(&fdb->nh_list);
> +		nexthop_put(old_nh);
> +	}
> +	rcu_assign_pointer(fdb->nh, nh);
> +	list_add_tail_rcu(&fdb->nh_list, &nh->fdb_list);
> +	return 1;
> +
> +err_inval:
> +	if (nh)
> +		nexthop_put(nh);
> +	return err;
> +}
> +
>  static int vxlan_fdb_create(struct vxlan_dev *vxlan,
>  			    const u8 *mac, union vxlan_addr *ip,
>  			    __u16 state, __be16 port, __be32 src_vni,
>  			    __be32 vni, __u32 ifindex, __u16 ndm_flags,
> -			    struct vxlan_fdb **fdb)
> +			    u32 nhid, struct vxlan_fdb **fdb,
> +			    struct netlink_ext_ack *extack)
>  {
>  	struct vxlan_rdst *rd = NULL;
>  	struct vxlan_fdb *f;
> @@ -838,20 +927,33 @@ static int vxlan_fdb_create(struct vxlan_dev *vxlan,
>  	if (!f)
>  		return -ENOMEM;
>  
> -	rc = vxlan_fdb_append(f, ip, port, vni, ifindex, &rd);
> -	if (rc < 0) {
> -		kfree(f);
> -		return rc;
> -	}
> +	if (nhid)
> +		rc = vxlan_fdb_nh_update(vxlan, f, nhid, extack);
> +	else
> +		rc = vxlan_fdb_append(f, ip, port, vni, ifindex, &rd);
> +	if (rc < 0)
> +		goto errout;
>  
>  	*fdb = f;
>  
>  	return 0;
> +
> +errout:
> +	kfree(f);
> +	return rc;
>  }
>  
>  static void __vxlan_fdb_free(struct vxlan_fdb *f)
>  {
>  	struct vxlan_rdst *rd, *nd;
> +	struct nexthop *nh;
> +
> +	nh = rcu_dereference_raw(f->nh);
> +	if (nh) {
> +		rcu_assign_pointer(f->nh, NULL);
> +		list_del_rcu(&f->nh_list);
> +		nexthop_put(nh);
> +	}
>  
>  	list_for_each_entry_safe(rd, nd, &f->remotes, list) {
>  		dst_cache_destroy(&rd->dst_cache);
> @@ -875,10 +977,15 @@ static void vxlan_fdb_destroy(struct vxlan_dev *vxlan, struct vxlan_fdb *f,
>  	netdev_dbg(vxlan->dev, "delete %pM\n", f->eth_addr);
>  
>  	--vxlan->addrcnt;
> -	if (do_notify)
> -		list_for_each_entry(rd, &f->remotes, list)
> -			vxlan_fdb_notify(vxlan, f, rd, RTM_DELNEIGH,
> +	if (do_notify) {
> +		if (rcu_access_pointer(f->nh))
> +			vxlan_fdb_notify(vxlan, f, NULL, RTM_DELNEIGH,
>  					 swdev_notify, NULL);
> +		else
> +			list_for_each_entry(rd, &f->remotes, list)
> +				vxlan_fdb_notify(vxlan, f, rd, RTM_DELNEIGH,
> +						 swdev_notify, NULL);
> +	}
>  
>  	hlist_del_rcu(&f->hlist);
>  	call_rcu(&f->rcu, vxlan_fdb_free);
> @@ -897,7 +1004,7 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
>  				     __u16 state, __u16 flags,
>  				     __be16 port, __be32 vni,
>  				     __u32 ifindex, __u16 ndm_flags,
> -				     struct vxlan_fdb *f,
> +				     struct vxlan_fdb *f, u32 nhid,
>  				     bool swdev_notify,
>  				     struct netlink_ext_ack *extack)
>  {
> @@ -908,6 +1015,18 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
>  	int rc = 0;
>  	int err;
>  
> +	if (nhid && !rcu_access_pointer(f->nh)) {
> +		NL_SET_ERR_MSG(extack,
> +			       "Cannot replace an existing non nexthop fdb with a nexthop");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (nhid && (flags & NLM_F_APPEND)) {
> +		NL_SET_ERR_MSG(extack,
> +			       "Cannot append to a nexthop fdb");
> +		return -EOPNOTSUPP;
> +	}
> +
>  	/* Do not allow an externally learned entry to take over an entry added
>  	 * by the user.
>  	 */
> @@ -929,10 +1048,18 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
>  		/* Only change unicasts */
>  		if (!(is_multicast_ether_addr(f->eth_addr) ||
>  		      is_zero_ether_addr(f->eth_addr))) {
> -			rc = vxlan_fdb_replace(f, ip, port, vni,
> -					       ifindex, &oldrd);
> +			if (nhid) {
> +				rc = vxlan_fdb_nh_update(vxlan, f, nhid, extack);
> +				if (rc < 0)
> +					return rc;
> +			} else {
> +				rc = vxlan_fdb_replace(f, ip, port, vni,
> +						       ifindex, &oldrd);
> +			}
>  			notify |= rc;
>  		} else {
> +			NL_SET_ERR_MSG(extack,
> +			       "Cannot replace non-unicast fdb entries");
>  			return -EOPNOTSUPP;
>  		}
>  	}
> @@ -962,6 +1089,8 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
>  	return 0;
>  
>  err_notify:
> +	if (nhid)
> +		return err;
>  	if ((flags & NLM_F_REPLACE) && rc)
>  		*rd = oldrd;
>  	else if ((flags & NLM_F_APPEND) && rc) {
> @@ -975,7 +1104,7 @@ static int vxlan_fdb_update_create(struct vxlan_dev *vxlan,
>  				   const u8 *mac, union vxlan_addr *ip,
>  				   __u16 state, __u16 flags,
>  				   __be16 port, __be32 src_vni, __be32 vni,
> -				   __u32 ifindex, __u16 ndm_flags,
> +				   __u32 ifindex, __u16 ndm_flags, u32 nhid,
>  				   bool swdev_notify,
>  				   struct netlink_ext_ack *extack)
>  {
> @@ -990,7 +1119,7 @@ static int vxlan_fdb_update_create(struct vxlan_dev *vxlan,
>  
>  	netdev_dbg(vxlan->dev, "add %pM -> %pIS\n", mac, ip);
>  	rc = vxlan_fdb_create(vxlan, mac, ip, state, port, src_vni,
> -			      vni, ifindex, fdb_flags, &f);
> +			      vni, ifindex, fdb_flags, nhid, &f, extack);
>  	if (rc < 0)
>  		return rc;
>  
> @@ -1012,7 +1141,7 @@ static int vxlan_fdb_update(struct vxlan_dev *vxlan,
>  			    const u8 *mac, union vxlan_addr *ip,
>  			    __u16 state, __u16 flags,
>  			    __be16 port, __be32 src_vni, __be32 vni,
> -			    __u32 ifindex, __u16 ndm_flags,
> +			    __u32 ifindex, __u16 ndm_flags, u32 nhid,
>  			    bool swdev_notify,
>  			    struct netlink_ext_ack *extack)
>  {
> @@ -1028,14 +1157,15 @@ static int vxlan_fdb_update(struct vxlan_dev *vxlan,
>  
>  		return vxlan_fdb_update_existing(vxlan, ip, state, flags, port,
>  						 vni, ifindex, ndm_flags, f,
> -						 swdev_notify, extack);
> +						 nhid, swdev_notify, extack);
>  	} else {
>  		if (!(flags & NLM_F_CREATE))
>  			return -ENOENT;
>  
>  		return vxlan_fdb_update_create(vxlan, mac, ip, state, flags,
>  					       port, src_vni, vni, ifindex,
> -					       ndm_flags, swdev_notify, extack);
> +					       ndm_flags, nhid, swdev_notify,
> +					       extack);
>  	}
>  }
>  
> @@ -1049,7 +1179,7 @@ static void vxlan_fdb_dst_destroy(struct vxlan_dev *vxlan, struct vxlan_fdb *f,
>  
>  static int vxlan_fdb_parse(struct nlattr *tb[], struct vxlan_dev *vxlan,
>  			   union vxlan_addr *ip, __be16 *port, __be32 *src_vni,
> -			   __be32 *vni, u32 *ifindex)
> +			   __be32 *vni, u32 *ifindex, u32 *nhid)
>  {
>  	struct net *net = dev_net(vxlan->dev);
>  	int err;
> @@ -1109,6 +1239,11 @@ static int vxlan_fdb_parse(struct nlattr *tb[], struct vxlan_dev *vxlan,
>  		*ifindex = 0;
>  	}
>  
> +	if (tb[NDA_NH_ID])
> +		*nhid = nla_get_u32(tb[NDA_NH_ID]);
> +	else
> +		*nhid = 0;
> +
>  	return 0;
>  }
>  
> @@ -1123,7 +1258,7 @@ static int vxlan_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],
>  	union vxlan_addr ip;
>  	__be16 port;
>  	__be32 src_vni, vni;
> -	u32 ifindex;
> +	u32 ifindex, nhid;
>  	u32 hash_index;
>  	int err;
>  
> @@ -1133,10 +1268,11 @@ static int vxlan_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],
>  		return -EINVAL;
>  	}
>  
> -	if (tb[NDA_DST] == NULL)
> +	if (!tb || (!tb[NDA_DST] && !tb[NDA_NH_ID]))
>  		return -EINVAL;
>  
> -	err = vxlan_fdb_parse(tb, vxlan, &ip, &port, &src_vni, &vni, &ifindex);
> +	err = vxlan_fdb_parse(tb, vxlan, &ip, &port, &src_vni, &vni, &ifindex,
> +			      &nhid);
>  	if (err)
>  		return err;
>  
> @@ -1148,7 +1284,7 @@ static int vxlan_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],
>  	err = vxlan_fdb_update(vxlan, addr, &ip, ndm->ndm_state, flags,
>  			       port, src_vni, vni, ifindex,
>  			       ndm->ndm_flags | NTF_VXLAN_ADDED_BY_USER,
> -			       true, extack);
> +			       nhid, true, extack);
>  	spin_unlock_bh(&vxlan->hash_lock[hash_index]);
>  
>  	return err;
> @@ -1159,8 +1295,8 @@ static int __vxlan_fdb_delete(struct vxlan_dev *vxlan,
>  			      __be16 port, __be32 src_vni, __be32 vni,
>  			      u32 ifindex, bool swdev_notify)
>  {
> -	struct vxlan_fdb *f;
>  	struct vxlan_rdst *rd = NULL;
> +	struct vxlan_fdb *f;
>  	int err = -ENOENT;
>  
>  	f = vxlan_find_mac(vxlan, addr, src_vni);
> @@ -1195,12 +1331,13 @@ static int vxlan_fdb_delete(struct ndmsg *ndm, struct nlattr *tb[],
>  	struct vxlan_dev *vxlan = netdev_priv(dev);
>  	union vxlan_addr ip;
>  	__be32 src_vni, vni;
> -	__be16 port;
> -	u32 ifindex;
> +	u32 ifindex, nhid;
>  	u32 hash_index;
> +	__be16 port;
>  	int err;
>  
> -	err = vxlan_fdb_parse(tb, vxlan, &ip, &port, &src_vni, &vni, &ifindex);
> +	err = vxlan_fdb_parse(tb, vxlan, &ip, &port, &src_vni, &vni, &ifindex,
> +			      &nhid);
>  	if (err)
>  		return err;
>  
> @@ -1228,6 +1365,17 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
>  		hlist_for_each_entry_rcu(f, &vxlan->fdb_head[h], hlist) {
>  			struct vxlan_rdst *rd;
>  
> +			if (rcu_access_pointer(f->nh)) {
> +				err = vxlan_fdb_info(skb, vxlan, f,
> +						     NETLINK_CB(cb->skb).portid,
> +						     cb->nlh->nlmsg_seq,
> +						     RTM_NEWNEIGH,
> +						     NLM_F_MULTI, NULL);
> +				if (err < 0)
> +					goto out;
> +				continue;
> +			}
> +
>  			list_for_each_entry_rcu(rd, &f->remotes, list) {
>  				if (*idx < cb->args[2])
>  					goto skip;
> @@ -1311,6 +1459,10 @@ static bool vxlan_snoop(struct net_device *dev,
>  		if (f->state & (NUD_PERMANENT | NUD_NOARP))
>  			return true;
>  
> +		/* Don't override an fdb with nexthop with a learnt entry */
> +		if (rcu_access_pointer(f->nh))
> +			return true;
> +
>  		if (net_ratelimit())
>  			netdev_info(dev,
>  				    "%pM migrated from %pIS to %pIS\n",
> @@ -1333,7 +1485,7 @@ static bool vxlan_snoop(struct net_device *dev,
>  					 vxlan->cfg.dst_port,
>  					 vni,
>  					 vxlan->default_dst.remote_vni,
> -					 ifindex, NTF_SELF, true, NULL);
> +					 ifindex, NTF_SELF, 0, true, NULL);
>  		spin_unlock(&vxlan->hash_lock[hash_index]);
>  	}
>  
> @@ -2616,6 +2768,32 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
>  	kfree_skb(skb);
>  }
>  
> +static void vxlan_xmit_nh(struct sk_buff *skb, struct net_device *dev,
> +			  struct vxlan_fdb *f, __be32 vni, bool did_rsc)
> +{
> +	struct vxlan_rdst nh_rdst;
> +	struct nexthop *nh;
> +	bool do_xmit;
> +	u32 hash;
> +
> +	memset(&nh_rdst, 0, sizeof(struct vxlan_rdst));
> +	hash = skb_get_hash(skb);
> +
> +	rcu_read_lock();
> +	nh = rcu_dereference(f->nh);
> +	if (!nh) {

Shouldn't you also kfree_skb() in this error case?
Below it seems we don't do anything else with the skb.

> +		rcu_read_unlock();
> +		return;
> +	}
> +	do_xmit = vxlan_fdb_nh_path_select(nh, hash, &nh_rdst);
> +	rcu_read_unlock();
> +
> +	if (likely(do_xmit))
> +		vxlan_xmit_one(skb, dev, vni, &nh_rdst, did_rsc);
> +	else
> +		kfree_skb(skb);
> +}
> +
>  /* Transmit local packets over Vxlan
>   *
>   * Outer IP header inherits ECN and DF from inner header.
> @@ -2692,22 +2870,27 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
>  		}
>  	}
>  
> -	list_for_each_entry_rcu(rdst, &f->remotes, list) {
> -		struct sk_buff *skb1;
> +	if (rcu_access_pointer(f->nh)) {
> +		vxlan_xmit_nh(skb, dev, f,
> +			      (vni ? : vxlan->default_dst.remote_vni), did_rsc);
> +	} else {
> +		list_for_each_entry_rcu(rdst, &f->remotes, list) {
> +			struct sk_buff *skb1;
>  
> -		if (!fdst) {
> -			fdst = rdst;
> -			continue;
> +			if (!fdst) {
> +				fdst = rdst;
> +				continue;
> +			}
> +			skb1 = skb_clone(skb, GFP_ATOMIC);
> +			if (skb1)
> +				vxlan_xmit_one(skb1, dev, vni, rdst, did_rsc);
>  		}
> -		skb1 = skb_clone(skb, GFP_ATOMIC);
> -		if (skb1)
> -			vxlan_xmit_one(skb1, dev, vni, rdst, did_rsc);
> +		if (fdst)
> +			vxlan_xmit_one(skb, dev, vni, fdst, did_rsc);
> +		else
> +			kfree_skb(skb);
>  	}
>  
> -	if (fdst)
> -		vxlan_xmit_one(skb, dev, vni, fdst, did_rsc);
> -	else
> -		kfree_skb(skb);
>  	return NETDEV_TX_OK;
>  }
>  
> @@ -3615,7 +3798,7 @@ static int __vxlan_dev_create(struct net *net, struct net_device *dev,
>  				       dst->remote_vni,
>  				       dst->remote_vni,
>  				       dst->remote_ifindex,
> -				       NTF_SELF, &f);
> +				       NTF_SELF, 0, &f, extack);
>  		if (err)
>  			return err;
>  	}
> @@ -4013,7 +4196,7 @@ static int vxlan_changelink(struct net_device *dev, struct nlattr *tb[],
>  					       vxlan->cfg.dst_port,
>  					       conf.vni, conf.vni,
>  					       conf.remote_ifindex,
> -					       NTF_SELF, true, extack);
> +					       NTF_SELF, 0, true, extack);
>  			if (err) {
>  				spin_unlock_bh(&vxlan->hash_lock[hash_index]);
>  				netdev_adjacent_change_abort(dst->remote_dev,
> @@ -4335,7 +4518,7 @@ vxlan_fdb_external_learn_add(struct net_device *dev,
>  			       fdb_info->remote_vni,
>  			       fdb_info->remote_ifindex,
>  			       NTF_USE | NTF_SELF | NTF_EXT_LEARNED,
> -			       false, extack);
> +			       0, false, extack);
>  	spin_unlock_bh(&vxlan->hash_lock[hash_index]);
>  
>  	return err;
> diff --git a/include/net/vxlan.h b/include/net/vxlan.h
> index 373aadc..3a41627c 100644
> --- a/include/net/vxlan.h
> +++ b/include/net/vxlan.h
> @@ -7,6 +7,7 @@
>  #include <net/dst_metadata.h>
>  #include <net/rtnetlink.h>
>  #include <net/switchdev.h>
> +#include <net/nexthop.h>
>  
>  #define IANA_VXLAN_UDP_PORT     4789
>  
> @@ -487,4 +488,28 @@ static inline void vxlan_flag_attr_error(int attrtype,
>  #undef VXLAN_FLAG
>  }
>  
> +static inline bool vxlan_fdb_nh_path_select(struct nexthop *nh,
> +					    int hash,
> +					    struct vxlan_rdst *rdst)
> +{
> +	struct fib_nh_common *nhc;
> +
> +	nhc = nexthop_path_fdb_result(nh, hash);
> +	if (unlikely(!nhc))
> +		return false;
> +
> +	switch (nhc->nhc_gw_family) {
> +	case AF_INET:
> +		rdst->remote_ip.sin.sin_addr.s_addr = nhc->nhc_gw.ipv4;
> +		rdst->remote_ip.sa.sa_family = AF_INET;
> +		break;
> +	case AF_INET6:
> +		rdst->remote_ip.sin6.sin6_addr = nhc->nhc_gw.ipv6;
> +		rdst->remote_ip.sa.sa_family = AF_INET6;
> +		break;
> +	}
> +
> +	return true;
> +}
> +
>  #endif
> diff --git a/include/uapi/linux/neighbour.h b/include/uapi/linux/neighbour.h
> index cd144e3..eefcda8 100644
> --- a/include/uapi/linux/neighbour.h
> +++ b/include/uapi/linux/neighbour.h
> @@ -29,6 +29,7 @@ enum {
>  	NDA_LINK_NETNSID,
>  	NDA_SRC_VNI,
>  	NDA_PROTOCOL,  /* Originator of entry */
> +	NDA_NH_ID,
>  	__NDA_MAX
>  };
>  
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index b607ea6..37e4dba 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -1771,6 +1771,7 @@ static struct neigh_table *neigh_find_table(int family)
>  }
>  
>  const struct nla_policy nda_policy[NDA_MAX+1] = {
> +	[NDA_UNSPEC]		= { .strict_start_type = NDA_NH_ID },
>  	[NDA_DST]		= { .type = NLA_BINARY, .len = MAX_ADDR_LEN },
>  	[NDA_LLADDR]		= { .type = NLA_BINARY, .len = MAX_ADDR_LEN },
>  	[NDA_CACHEINFO]		= { .len = sizeof(struct nda_cacheinfo) },
> @@ -1781,6 +1782,7 @@ const struct nla_policy nda_policy[NDA_MAX+1] = {
>  	[NDA_IFINDEX]		= { .type = NLA_U32 },
>  	[NDA_MASTER]		= { .type = NLA_U32 },
>  	[NDA_PROTOCOL]		= { .type = NLA_U8 },
> +	[NDA_NH_ID]		= { .type = NLA_U32 },
>  };
>  
>  static int neigh_delete(struct sk_buff *skb, struct nlmsghdr *nlh,
> 

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