Re: [PATCH v5 bpf-next 3/9] veth: Avoid drops by oversized packets when XDP is enabled

[Jakub Kicinski]

On Thu, 26 Jul 2018 23:40:26 +0900, Toshiaki Makita wrote:
> +             max_mtu = PAGE_SIZE - VETH_XDP_HEADROOM -
> +                       peer->hard_header_len -
> +                       SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> +             if (peer->mtu > max_mtu) {
> +                     NL_SET_ERR_MSG_MOD(extack, "Peer MTU is too large to 
> set XDP");
> +                     err = -ERANGE;
> +                     goto err;
> +             }

You need to add .ndo_change_mtu and check this condition there too.