Subject: Re: [PATCH net-next v2 02/14] i40e: support generic devlink param "max_mac_per_vf"

From: Jakub Kicinski <[email-masked]>
Date: Tue, 21 Oct 2025 16:07:45 -0700

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?