netdev - Re: [PATCH v3] virtio: Work around frames incorrectly marked as gso

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Date:   Mon, 24 Feb 2020 14:27:42 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     anton.ivanov@...bridgegreys.com
Cc:     Network Development <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        linux-um@...ts.infradead.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v3] virtio: Work around frames incorrectly marked as gso

On Mon, Feb 24, 2020 at 8:26 AM <anton.ivanov@...bridgegreys.com> wrote:
>
> From: Anton Ivanov <anton.ivanov@...bridgegreys.com>
>
> Some of the locally generated frames marked as GSO which
> arrive at virtio_net_hdr_from_skb() have no GSO_TYPE, no
> fragments (data_len = 0) and length significantly shorter
> than the MTU (752 in my experiments).

Do we understand how these packets are generated? Else it seems this
might be papering over a deeper problem.

The stack should not create GSO packets less than or equal to
skb_shinfo(skb)->gso_size. See for instance the check in
tcp_gso_segment after pulling the tcp header:

        mss = skb_shinfo(skb)->gso_size;
        if (unlikely(skb->len <= mss))
                goto out;

What is the gso_type, and does it include SKB_GSO_DODGY?