netdev - Re: [PATCH net v2] net: accept UFO datagrams from tuntap and packet

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Date:   Wed, 22 Nov 2017 20:54:55 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, mkubecek@...e.cz,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net v2] net: accept UFO datagrams from tuntap and packet



On 2017年11月21日 23:22, Willem de Bruijn wrote:
> From: Willem de Bruijn<willemb@...gle.com>
>
> Tuntap and similar devices can inject GSO packets. Accept type
> VIRTIO_NET_HDR_GSO_UDP, even though not generating UFO natively.
>
> Processes are expected to use feature negotiation such as TUNSETOFFLOAD
> to detect supported offload types and refrain from injecting other
> packets. This process breaks down with live migration: guest kernels
> do not renegotiate flags, so destination hosts need to expose all
> features that the source host does.
>
> Partially revert the UFO removal from 182e0b6b5846~1..d9d30adf5677.
> This patch introduces nearly(*) no new code to simplify verification.
> It brings back verbatim tuntap UFO negotiation, VIRTIO_NET_HDR_GSO_UDP
> insertion and software UFO segmentation.
>
> It does not reinstate protocol stack support, hardware offload
> (NETIF_F_UFO), SKB_GSO_UDP tunneling in SKB_GSO_SOFTWARE or reception
> of VIRTIO_NET_HDR_GSO_UDP packets in tuntap.
>
> To support SKB_GSO_UDP reappearing in the stack, also reinstate
> logic in act_csum and openvswitch. Achieve equivalence with v4.13 HEAD
> by squashing in commit 939912216fa8 ("net: skb_needs_check() removes
> CHECKSUM_UNNECESSARY check for tx.") and reverting commit 8d63bee643f1
> ("net: avoid skb_warn_bad_offload false positives on UFO").
>
> (*) To avoid having to bring back skb_shinfo(skb)->ip6_frag_id,
> ipv6_proxy_select_ident is changed to return a __be32 and this is
> assigned directly to the frag_hdr. Also, SKB_GSO_UDP is inserted
> at the end of the enum to minimize code churn.
>
> Tested
>    Booted a v4.13 guest kernel with QEMU. On a host kernel before this
>    patch `ethtool -k eth0` shows UFO disabled. After the patch, it is
>    enabled, same as on a v4.13 host kernel.
>
>    A UFO packet sent from the guest appears on the tap device:
>      host:
>        nc -l -p -u 8000 &
>        tcpdump -n -i tap0
>
>      guest:
>        dd if=/dev/zero of=payload.txt bs=1 count=2000
>        nc -u 192.16.1.1 8000 < payload.txt
>
>    Direct tap to tap transmission of VIRTIO_NET_HDR_GSO_UDP succeeds,
>    packets arriving fragmented:
>
>      ./with_tap_pair.sh ./tap_send_ufo tap0 tap1
>      (fromhttps://github.com/wdebruij/kerneltools/tree/master/tests)
>
> Changes
>    v1 -> v2
>      - simplified set_offload change (review comment)
>      - documented test procedure
>
> Link:http://lkml.kernel.org/r/<CAF=yD-LuUeDuL9YWPJD9ykOZ0QCjNeznPDr6whqZ9NGMNF12Mw@...l.gmail.com>
> Fixes: fb652fdfe837 ("macvlan/macvtap: Remove NETIF_F_UFO advertisement.")
> Reported-by: Michal Kubecek<mkubecek@...e.cz>
> Signed-off-by: Willem de Bruijn<willemb@...gle.com>
> ---

Have done netperf UDP_STREAM between two 4.8 guests. The patch works as 
expected.

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks