linux-kernel - Re: [PATCH net-next v2 2/3] net: ethernet: ti: am65-cpsw: enable bc/mc storm prevention support

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Date:   Thu, 4 Nov 2021 01:19:24 +0200
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        <linux-omap@...r.kernel.org>, Tony Lindgren <tony@...mide.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next v2 2/3] net: ethernet: ti: am65-cpsw: enable
 bc/mc storm prevention support



On 04/11/2021 01:07, Jakub Kicinski wrote:
> On Thu, 4 Nov 2021 00:20:30 +0200 Grygorii Strashko wrote:
>> On 03/11/2021 02:38, Jakub Kicinski wrote:
>>> On Mon, 1 Nov 2021 19:01:21 +0200 Grygorii Strashko wrote:
>>>>    - 01:00:00:00:00:00 fixed value has to be used for MC packets rate
>>>>      limiting (exact match)
>>>
>>> This looks like a stretch, why not use a mask? You can require users to
>>> always install both BC and MC rules if you want to make sure the masked
>>> rule does not match BC.
>>>    
>>
>> Those matching rules are hard coded in HW for packet rate limiting and SW only
>> enables them and sets requested pps limit.
>> - 1:BC: HW does exact match on BC MAC address
>> - 2:MC: HW does match on MC bit (the least-significant bit of the first octet)
>>
>> Therefore the exact match done in this patch for above dst_mac's with
>> is_broadcast_ether_addr() and ether_addr_equal().
> 
> Right but flower supports masked matches for dest address, as far as I
> can tell. So you should check the mask is what you expect as well, not
> just look at the key. Mask should be equal to key in your case IIUC, so:
> 
> 	if (is_broadcast_ether_addr(match.key->dst) &&
> 	    is_broadcast_ether_addr(match.mask->dst))
> 
> and
> 
> 	if (!memcmp(match.key->dst, mc_mac, ETH_ALEN) &&
> 	    !memcmp(match.mask->dst, mc_mac, ETH_ALEN))
> 
> I think you should also test that the mask, not the key of source addr
> is zero.
> 
> Note that ether_addr_equal() assumes the mac address is alinged to 2,
> which I'm not sure is the case here.
> 
> Also you can make mc_mac a static const.

Ah, got it. Thank you.

> 
>> The K3 cpsw also supports number configurable policiers (bit rate limit) in
>> ALE for which supports is to be added, and for them MC mask (sort of, it uses
>> number of ignored bits, like FF-FF-FF-00-00-00) can be used.

-- 
Best regards,
grygorii