From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grygorii Strashko Subject: Re: [PATCH net-next] net: ethernet: ti: cpsw: don't flush mcast entries while switch promisc mode Date: Fri, 19 Oct 2018 12:23:28 -0500 Message-ID: <36da9bb2-38b7-cc70-9569-8895e20c6d1f@ti.com> References: <20181018180006.7065-1-ivan.khoronzhuk@linaro.org> <6c34a3ce-dbee-538e-bda7-8dd485315267@ti.com> <20181019120408.GA3909@khorivan> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit To: , , , Return-path: In-Reply-To: <20181019120408.GA3909@khorivan> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 10/19/18 7:04 AM, Ivan Khoronzhuk wrote: > On Thu, Oct 18, 2018 at 07:03:06PM -0500, Grygorii Strashko wrote: >> >> >> On 10/18/18 1:00 PM, Ivan Khoronzhuk wrote: >>> No need now to flush mcast entries in switch mode while toggling to >>> promiscuous mode. It's not needed as vlan reg_mcast = ALL_PORTS >>> and mcast/vlan ports = ALL_PORTS, the same happening for vlan >>> unreg_mcast, it's set to ALL_PORT_MASK just after calling promisc >>> mode routine by calling set allmulti. I suppose main reason to flush >>> them is to use unreg_mcast to receive all to host port. Thus, now, all >>> mcast packets are received anyway and no reason to flush mcast entries >>> unsafely, as they were synced with __dev_mc_sync() previously and are >>> not restored. Another way is to _dev_mc_unsync() them, but no need. >> >> User have possibility to add additional mcast entries or edit existing >> in switch-mode, which is now done using custom tool. So, Host in promisc >> mode will not receive packets for mcast address X if port mask for this >> addr set to (ALL_PORTS - HOST_PORT). Am I missing smth? > > I didn't take into account the custom tool changing entries directly, > but even in this case there is at least a couple of interesting > questions: > > 1) Before the patch applied only several days ago - >   5da1948969bc1991920987ce4361ea56046e5a98 >   "ti: cpsw: fix lost of mcast packets while rx_mode update" >   It was impossible to do correctly anyway, as all mcast entries not >   in the mc list were flushed (after rx_mode cb), by: >   cpsw_ale_flush_multicast(cpsw->ale, ALE_ALL_PORTS, vid); >   and those in mc, rewritten by adding them back in corrected form. >   ... or this cb was not supposed to be called at all ... It's not allowed to manipulate ALE table in dual_mac mode, so your patches are safe in dual_mac mode. For switch-mode (unless we move forward with switch dev) standard linux interfaces allows create default mcast entries which then (if required) corrected using custom tool now. > > 2) What is the reason to add mcast switch entires >   (ALL_PORTS - HOST_PORT) if its function is added anyway by >   unreq_mcast & (ALL_PORTS - HOST_PORT) ? >   So, doesn't matter it's added or not - it will work :-|. because in switch mode not all traffic directed to the Host port - only in promisc mode. Reason safety and performance - Host should not receive traffic which is not designated for it. promiscuous in switch mode: - disables learning - enables unicast flooding to Host port - enables unregistered multi-cast flooding to the Host port In other words, CPSW will continue forwarding packets between P1&P2, but also will "duplicate" packets to Host port. This will work only for vlans which have host port as member. > > 3) Even so, toggling promisc mode will clear all these changes anyway, >   even I will call _dev_mc_unsync() after flushing them. there can be records which are not under control of Linux now. > > 4) If user can tune ALE table by hand, what stops him do it after moving >   to promisc mode, seems he knows what he's doing? > > 5) It could be possible only for not default vlan entries, but mcast >   vlan support is not supported yet. Who is gona restore those >   entries after promisc off? > > This behaviour is arguable, and flushing mcast entries can bring more > issues then leaving. For me it doesn't matter, I can archive the same > by adding after flush one line, it's even shorter: > __dev_mc_unsync(priv->ndev, NULL); Again, unless we move forward with switch dev you can't assume that Linux stack has full control over ALE table. Sry, hence this patch is not a fix and can introduce changes in current behavior and cause regression reports - NACK. -- regards, -grygorii