netdev - RE: [PATCH net-next v3 2/3] net/macsec: Add MACsec skb extension Rx Data path support

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Message-ID: <PH0PR12MB54490D24F44759ACDABC950FBF869@PH0PR12MB5449.namprd12.prod.outlook.com>
Date:   Tue, 12 Jul 2022 06:50:52 +0000
From:   Lior Nahmanson <liorna@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Paolo Abeni <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Raed Salem <raeds@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Yossi Kuperman <yossiku@...dia.com>
Subject: RE: [PATCH net-next v3 2/3] net/macsec: Add MACsec skb extension Rx
 Data path support

 > On Tue, 21 Jun 2022 12:39:23 +0000 Lior Nahmanson wrote:
> > > Shooting from the hip a little bit, but macsec being a tightly bound
> > > L2 upper maybe metadata dst is a workable solution for carrying the
> > > sci and offload status between upper and lower? The range of values
> > > should be well known and limited.
> >
> > Under the assumption that by skb_metadata you meant metadata_dst,
> 
> Can you show me in my email where I said skb_metadata?
> 
> > I think there are few reasons why i think is better to use skb extensions:
> >
> > 1. Unlike skb extension, the metadata_dst deallaction is handled directly by
> the allocator.
> > Since the sci and offloaded fields are shared between the MACsec
> > driver and the offload driver (in our case mlx5 driver), for Rx, the
> > metadata_dst allocation is done in the mlx5 driver, while the dealloction
> should be done in the MACsec driver.
> > This is undesired behavior.
> 
> You allocate metadata skb once and then attach it to the skbs.
> 
> > 2. medadata_dst is attached to the skb using skb_dst_set(), which set the
> slow_gro bit.
> > So there is no gain regarding slow_gro flow.
> >
> > 3. metadata_dst allocation require much more memory than needed for
> > MACsec use case (mainly because struct dst_entry which seems redundant
> for this case).

i considered the usage of skb_metadata_dst, however i still think
that skb_ext will fit more to MACsec offload implementation for the following reasons:
1. for Rx, each skb can have a different SCI and offloaded values which mandate allocation
    of metadata_dst for each skb which contradicts the desired usage for skb_metadata_dst where
    it's allocated once and a refcnt held whenever used.
2. skb_ext method is used in a similar IPsec offload implementation which in the future could make it easier
    to refactor this section to unify all crypto offloads skb_ext usage.

apologize for the late respond.