Re: [PATCH v1 net-next 4/6] net: mscc: ocelot: VCAP IS1 support

[Allan W. Nielsen]

Hi Vladimir,

On 06.05.2020 13:53, Vladimir Oltean wrote:
> On Wed, 6 May 2020 at 12:45, Allan W. Nielsen
> <allan.nielsen@xxxxxxxxxxxxx> wrote:
> > Hi Xiaoliang,
> >
> > On 06.05.2020 15:48, Xiaoliang Yang wrote:
> > >VCAP IS1 is a VCAP module which can filter MAC, IP, VLAN, protocol, and
> > >TCP/UDP ports keys, and do Qos and VLAN retag actions.
> > >This patch added VCAP IS1 support in ocelot ace driver, which can supports
> > >vlan modify action of tc filter.
> > >Usage:
> > >        tc qdisc add dev swp0 ingress
> > >        tc filter add dev swp0 protocol 802.1Q parent ffff: flower \
> > >        skip_sw vlan_id 1 vlan_prio 1 action vlan modify id 2 priority 2
> > I skimmed skimmed through the patch serie, and the way I understood it
> > is that you look at the action, and if it is a VLAN operation, then you
> > put it in IS1 and if it is one of the other then put it in IS2.
> >
> > This is how the HW is designed - I'm aware of that.
> >
> > But how will this work if you have 2 rules, 1 modifying the VLAN and
> > another rule dropping certain packets?
>
> At the moment, the driver does not support more than 1 action. We
> might need to change that, but we can still install more filters with
> the same key and still be fine (see more below). When there is more
> than 1 action, the IS1 stuff will be combined into a single rule
> programmed into IS1, and the IS2 stuff will be combined into a single
> new rule with the same keys installed into VCAP IS2. Would that not
> work?
>
> > The SW model have these two rules in the same table, and can stop
> > process at the first match. SW will do the action of the first frame
> > matching.
>
> Actually I think this is an incorrect assumption - software stops at
> the first action only if told to do so. Let me copy-paste a text from
> a different email thread.

I'm still not able to see how this proposal will give us the same
behavioral in SW and in HW.

A simple example:

tc qdisc add dev enp0s3 ingress
tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
    prio 10 flower vlan_id 5 action vlan modify id 10
tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
    prio 20 flower src_mac 00:00:00:00:00:08 action drop

We can then inject a frame with VID 5 and smac ::08:
$ ef tx tap0 eth smac 00:00:00:00:00:08 ctag vid 5 

We can then check the filter and see that it only hit the first rule:

$ tc -s filter show dev enp0s3 ingress
filter protocol 802.1Q pref 10 flower chain 0
filter protocol 802.1Q pref 10 flower chain 0 handle 0x1
  vlan_id 5
  not_in_hw
        action order 1: vlan  modify id 10 protocol 802.1Q priority 0 pipe
         index 1 ref 1 bind 1 installed 19 sec used 6 sec
        Action statistics:
        Sent 42 bytes 1 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

filter protocol 802.1Q pref 20 flower chain 0
filter protocol 802.1Q pref 20 flower chain 0 handle 0x1
  src_mac 00:00:00:00:00:08
  not_in_hw
        action order 1: gact action drop
         random type none pass val 0
         index 1 ref 1 bind 1 installed 11 sec used 11 sec
        Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

If this was done with the proposed HW offload, then both rules would
have been hit and we would have a different behavioral.

This can be fixed by adding the "continue" action to the first rule:

tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
    prio 10 flower vlan_id 5 action vlan modify id 10 continue
tc filter add dev enp0s3 protocol 802.1Q parent ffff: \
    prio 20 flower src_mac 00:00:00:00:00:08 action drop

But that would again break if we add 2 rules manipulating the VLAN (as
the HW does not continue with in a single TCAM).

My point is: I do not think we can hide the fact that this is done
in independent TCAMs in the silicon.

I think it is possible to do this with the chain feature (even though it
is not a perfect match), but it would require more analysis.

/Allan