Petr says: When offloading GRE tunnels, the MTU setting is kept fixed after the initial offload even as the slow-path configuration changed. Worse: the offloaded MTU setting is actually just a transient value set at the time of NETDEV_REGISTER of the tunnel. As of commit ffc2b6ee4174 ("ip_gre: fix IFLA_MTU ignored on NEWLINK"), that transient value is zero, and unless there's e.g. a VRF migration that prompts re-offload, it stays at zero, and all GRE packets end up trapping.
Thus, in patch #1, change the way the MTU is changed post-registration, so that the full event protocol is observed. That way the drivers get to see the change and have a chance to react. In the remaining two patches, implement support for MTU change in mlxsw driver. Petr Machata (3): ip_tunnel: Emit events for post-register MTU changes mlxsw: spectrum_router: Move mlxsw_sp_rif_ipip_lb_op() mlxsw: spectrum_router: Handle MTU change of GRE netdevs .../net/ethernet/mellanox/mlxsw/spectrum_router.c | 78 ++++++++++++++-------- net/ipv4/ip_tunnel.c | 26 ++++++-- 2 files changed, 72 insertions(+), 32 deletions(-) -- 2.14.3