netdev - Re: tc H/W offload issue with vxlan tunnels [was: nfp: flower vxlan tunnel offload]

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Date:   Wed, 27 Sep 2017 14:55:09 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Or Gerlitz <gerlitz.or@...il.com>, Jiri Benc <jbenc@...hat.com>,
        Simon Horman <simon.horman@...ronome.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com, John Hurley <john.hurley@...ronome.com>,
        Paul Blakey <paulb@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>
Subject: Re: tc H/W offload issue with vxlan tunnels [was: nfp: flower vxlan
 tunnel offload]

Wed, Sep 27, 2017 at 02:31:36PM CEST, pabeni@...hat.com wrote:
>On Wed, 2017-09-27 at 13:11 +0200, Jiri Pirko wrote:
>> Wed, Sep 27, 2017 at 11:46:58AM CEST, pabeni@...hat.com wrote:
>> > On Wed, 2017-09-27 at 11:17 +0200, Jiri Pirko wrote:
>> > > Wed, Sep 27, 2017 at 10:29:35AM CEST, pabeni@...hat.com wrote:
>> > > > So it looks like the H/W offload hook will still be called with the
>> > > > same arguments in both case, and 'bad' rule will still be pushed to the
>> > > > H/W as the driver itself has no way to distinct between the two
>> > > > scenarios.
>> > > 
>> > > Why "bad"?
>> > 
>> > Such rule is coped differently by the SW and the HW data path.
>> > 
>> > a rule like:
>> > 
>> > tc filter add dev eth0 protocol ip parent ffff: flower \
>> >   enc_key_id 102 enc_dst_port 4789 src_ip 3.4.5.6 skip_hw \
>> >   action action mirred redirect eth0_vf_1
>> > 
>> > will match 0 packets, while:
>> > 
>> > tc filter add dev eth0 protocol ip parent ffff: flower \
>> >   enc_key_id 102 enc_dst_port 4789 src_ip 3.4.5.6 skip_sw \
>> >   action action mirred redirect eth0_vf_1
>> > 
>> > [just flipped 'skip_sw' and 'skip_hw' ]
>> > will match the vxlan-tunneled packets. I understand that one of the
>> > design goal for the h/w offload path is being consistent with the sw
>> > one, but that does not hold in the above scenario.
>> 
>> Sure, the consistency is important. Howcome "skip_hw" won't match and
>> "skip_sw" will match? What's different?
>
>For the SW datapath, we need a metadata based/lwt tunnel to collect the
>tunnel information. eth0 is not a such device and does not provide the
>metadata. Any match on tunnel based field will fail - correctly.

So where do you attach the tc filter instead of eth0? vxlan0?


>
>When the HW datapath is used, the underlaying NIC is programmed exactly
>as done when we replace eth0 with vxlan0. The programmed flow matches
>vxlan encapsulated traffic.

Ok, so we should unify the behaviour with sw path and don't allow such
mathing in hw.


>
>Cheers,
>
>Paolo