vxlan: Age out FDB entries based on 'updated' time

Currently, the VXLAN driver ages out FDB entries based on their 'used'
time which is refreshed by both the Tx and Rx paths. This means that an
FDB entry will not age out if traffic is only forwarded to the target
host:

 # ip link add name vx1 up type vxlan id 10010 local 192.0.2.1 dstport 4789 learning ageing 10
 # bridge fdb add 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.1
 # bridge fdb get 00:11:22:33:44:55 br vx1 self
 00:11:22:33:44:55 dev vx1 dst 198.51.100.1 self
 # mausezahn vx1 -a own -b 00:11:22:33:44:55 -c 0 -p 100 -q &
 # sleep 20
 # bridge fdb get 00:11:22:33:44:55 br vx1 self
 00:11:22:33:44:55 dev vx1 dst 198.51.100.1 self

This is wrong as an FDB entry will remain present when we no longer have
an indication that the host is still behind the current remote. It is
also inconsistent with the bridge driver:

 # ip link add name br1 up type bridge ageing_time $((10 * 100))
 # ip link add name swp1 up master br1 type dummy
 # bridge fdb add 00:11:22:33:44:55 dev swp1 master dynamic
 # bridge fdb get 00:11:22:33:44:55 br br1
 00:11:22:33:44:55 dev swp1 master br1
 # mausezahn br1 -a own -b 00:11:22:33:44:55 -c 0 -p 100 -q &
 # sleep 20
 # bridge fdb get 00:11:22:33:44:55 br br1
 Error: Fdb entry not found.

Solve this by aging out entries based on their 'updated' time, which is
not refreshed by the Tx path:

 # ip link add name vx1 up type vxlan id 10010 local 192.0.2.1 dstport 4789 learning ageing 10
 # bridge fdb add 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.1
 # bridge fdb get 00:11:22:33:44:55 br vx1 self
 00:11:22:33:44:55 dev vx1 dst 198.51.100.1 self
 # mausezahn vx1 -a own -b 00:11:22:33:44:55 -c 0 -p 100 -q &
 # sleep 20
 # bridge fdb get 00:11:22:33:44:55 br vx1 self
 Error: Fdb entry not found.

But is refreshed by the Rx path:

 # ip address add 192.0.2.1/32 dev lo
 # ip link add name vx1 up type vxlan id 10010 local 192.0.2.1 dstport 4789 localbypass
 # ip link add name vx2 up type vxlan id 20010 local 192.0.2.1 dstport 4789 learning ageing 10
 # bridge fdb add 00:11:22:33:44:55 dev vx1 self static dst 127.0.0.1 vni 20010
 # mausezahn vx1 -a 00:aa:bb:cc:dd:ee -b 00:11:22:33:44:55 -c 0 -p 100 -q &
 # sleep 20
 # bridge fdb get 00:aa:bb:cc:dd:ee br vx2 self
 00:aa:bb:cc:dd:ee dev vx2 dst 127.0.0.1 self
 # pkill mausezahn
 # sleep 20
 # bridge fdb get 00:aa:bb:cc:dd:ee br vx2 self
 Error: Fdb entry not found.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20250204145549.1216254-7-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/vxlan/vxlan_core.c

@@ -2860,7 +2860,7 @@ static void vxlan_cleanup(struct timer_list *t)
 			if (f->flags & NTF_EXT_LEARNED)
 				continue;
 
-			timeout = READ_ONCE(f->used) + vxlan->cfg.age_interval * HZ;
+			timeout = READ_ONCE(f->updated) + vxlan->cfg.age_interval * HZ;
 			if (time_before_eq(timeout, jiffies)) {
 				netdev_dbg(vxlan->dev,
 					   "garbage collect %pM\n",