From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jakub Kicinski <jakub.kicinski@netronome.com>
Subject: Re: [PATCH v5 bpf-next 3/9] veth: Avoid drops by oversized packets
 when XDP is enabled
Date: Thu, 26 Jul 2018 17:51:27 -0700
Message-ID: <20180726175127.075185fc@cakuba.netronome.com>
References: <20180726144032.2116-1-toshiaki.makita1@gmail.com>
        <20180726144032.2116-4-toshiaki.makita1@gmail.com>
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Cc: netdev@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>,
        Jesper Dangaard Brouer <brouer@redhat.com>
To: Toshiaki Makita <toshiaki.makita1@gmail.com>
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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.