netdev - Re: [RFC net-next v2 5/5] net: phy: nxp-c45-tja11xx: implement mdo_insert_tx

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Date: Fri, 1 Sep 2023 11:32:19 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: Radu Pirea <radu-nicolae.pirea@....com>,
	"atenart@...nel.org" <atenart@...nel.org>,
	"Radu-nicolae Pirea (OSS)" <radu-nicolae.pirea@....nxp.com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	"hkallweit1@...il.com" <hkallweit1@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Sebastian Tobuschat <sebastian.tobuschat@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"richardcochran@...il.com" <richardcochran@...il.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC net-next v2 5/5] net: phy: nxp-c45-tja11xx: implement
 mdo_insert_tx_tag

On Fri, Sep 01, 2023 at 12:07:32PM +0200, Sabrina Dubroca wrote:
> 2023-09-01, 09:09:06 +0000, Radu Pirea wrote:
> > On Wed, 2023-08-30 at 13:35 +0200, Sabrina Dubroca wrote:
> > ...
> > 
> > > And it's not restored when the link goes back up? That's inconvenient
> > > :/
> > > Do we end up with inconsistent state? ie driver and core believe
> > > everything is still offloaded, but HW lost all state? do we leak
> > > some resources allocated by the driver?
> > 
> > Yes. We end up with inconsistent state. The HW will lost all state when
> > the phy is reseted. No resource is leaked, everything is there, but the
> > configuration needs to be reapplied.
> > 
> > > 
> > > We could add a flush/restore in macsec_notify when the lower device
> > > goes down/up, maybe limited to devices that request this (I don't
> > > know
> > > if all devices would need it, or maybe all devices offloading to the
> > > PHY but not to the MAC).
> > 
> > Agreed.
> > We can do a flush very simple, but to restore the configuration maybe
> > we should to save the key in the macsec_key structure. I am not sure if
> > the key can be extracted from crypto_aead structure.
> 
> Either that or in the driver. I have a small preference for driver,
> because then cases that don't need this restore won't have to keep the
> key in memory, reducing the likelihood of accidentally sharing it.
> OTOH, if we centralize that code, it's easier to make sure everything
> is cleared from kernel memory when we delete the SA.

Maybe consider about doing it as a library function, so drivers that
need this don't have to reimplement the functionality in randomly
buggy ways?

-- 
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