Message-ID: <075914db-d497-4428-97e2-256b35f40729@redhat.com>
Date: Wed, 22 Oct 2025 12:39:05 +0300
From: mohammad heib <mheib@...hat.com>
To: Jakub Kicinski <kuba@...nel.org>, Jacob Keller <jacob.e.keller@...el.com>
Cc: Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>,
 Alexander Lobakin <aleksander.lobakin@...el.com>, netdev@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 Aleksandr Loktionov <aleksandr.loktionov@...el.com>,
 Rafal Romanowski <rafal.romanowski@...el.com>
Subject: Re: [PATCH net-next v2 02/14] i40e: support generic devlink param
 "max_mac_per_vf"


Thank you for the review.

As Jacob Keller mentioned, this change enforces that a VF can never go 
above the maximum allowed value. However, there could still be other 
hardware-related restrictions.

Regarding the scenario you described, if the maximum is decreased to 2 
after VF1 has already added 4 filters, then the next time the user tries 
to add a new MAC address to VF1 (or to any VF that already has 2 or more 
MAC filters), they will see an error message in the kernel log:
  "Cannot add more MAC addresses: VF reached its maximum allowed limit 2"

I didn’t really consider the decreasing scenario, since this change is 
intended to be configured by the system administrator once, before 
setting up the VFs. If for some reason they decide to reduce the limit 
during the VF’s lifetime, I believe it’s the user’s responsibility to 
first remove the old MAC addresses and filters from the VF.


On 10/22/25 2:07 AM, Jakub Kicinski wrote:
> On Tue, 21 Oct 2025 13:39:27 -0700 Jacob Keller wrote:
>> On 10/20/2025 6:25 PM, Jakub Kicinski wrote:
>>> On Thu, 16 Oct 2025 23:08:31 -0700 Jacob Keller wrote:
>>>> - The configured value is a theoretical maximum. Hardware limits may
>>>>    still prevent additional MAC addresses from being added, even if the
>>>>    parameter allows it.
>>>
>>> Is "administrative policy" better than "theoretical max" ?
>>
>> That could be a bit more accurate.
>>
>>> Also -- should we be scanning the existing state to check if some VM
>>> hasn't violated the new setting and error or at least return a extack
>>> to the user to warn that the policy is not currently adhered to?
>>
>> My understanding here is that this enforces the VF to never go *above*
>> this value, but its possible some other hardware restriction (i.e. out
>> of filters) could prevent a VF from adding more filters even if the
>> value is set higher.
>>
>> Basically, this sets the maximum allowed number of filters, but doesn't
>> guarantee that many filters are actually available, at least on X710
>> where filters are a shared resource and we do not have a good mechanism
>> to coordinate across PFs to confirm how many have been made available or
>> reserved already. (Until firmware rejects adding a filter because
>> resources are capped)
>>
>> Thus, I don't think we need to scan to check anything here. VFs should
>> be unable to exceed this limit, and thats checked on filter add.
> 
> Sorry, just to be clear -- this comment is independent on the comment
> about "policy" vs "theoretical".
> 
> What if:
>   - max is set to 4
>   - VF 1 adds 4 filters
>   - (some time later) user asks to decrease max to 2
> 
> The devlink param is CMODE_RUNTIME so I'm assuming it can be tweaked
> at any point in time.
> 
> We probably don't want to prevent lowering the max as admin has no way
> to flush the filters. Either we don't let the knob be turned when SRIOV
> is enabled or we should warn if some VF has more filters than the new
> max?
> 

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