netdev - Re: [PATCH v2 01/17] psp: add documentation

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Message-ID: <685d5213a7682_2dcd9a29452@willemb.c.googlers.com.notmuch>
Date: Thu, 26 Jun 2025 09:58:43 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jakub Kicinski <kuba@...nel.org>, 
 Daniel Zahka <daniel.zahka@...il.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Donald Hunter <donald.hunter@...il.com>, 
 "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>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 Saeed Mahameed <saeedm@...dia.com>, 
 Leon Romanovsky <leon@...nel.org>, 
 Tariq Toukan <tariqt@...dia.com>, 
 Boris Pismenny <borisp@...dia.com>, 
 Kuniyuki Iwashima <kuniyu@...gle.com>, 
 Willem de Bruijn <willemb@...gle.com>, 
 David Ahern <dsahern@...nel.org>, 
 Neal Cardwell <ncardwell@...gle.com>, 
 Patrisious Haddad <phaddad@...dia.com>, 
 Raed Salem <raeds@...dia.com>, 
 Jianbo Liu <jianbol@...dia.com>, 
 Dragos Tatulea <dtatulea@...dia.com>, 
 Rahul Rameshbabu <rrameshbabu@...dia.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, 
 Toke Høiland-Jørgensen <toke@...hat.com>, 
 Alexander Lobakin <aleksander.lobakin@...el.com>, 
 Jacob Keller <jacob.e.keller@...el.com>, 
 netdev@...r.kernel.org
Subject: Re: [PATCH v2 01/17] psp: add documentation

Jakub Kicinski wrote:
> On Thu, 26 Jun 2025 07:55:34 -0400 Daniel Zahka wrote:
> > >> +after ``psp-versions-ena`` has been disabled. User may also disable
> > >> +``psp-versions-ena`` while there are active associations, which will
> > >> +break all PSP Rx processing.
> > >> +
> > >> +Drivers are expected to ensure that device key is usable upon init
> > >> +(working keys can be allocated), and that no duplicate keys may be generated
> > >> +(reuse of SPI without key rotation). Drivers may achieve this by rotating
> > >> +keys twice before registering the PSP device.  
> > > Since the device returns a { session_key, spi } pair, risk of reuse
> > > is purely in firmware.
> 
> I don't think this is a requirement put forward in the spec?
> Specifically if a device wants to allow partitioning of the SPI
> space it may let the host pick the SPI. To me the device allocating 
> the SPIs seemed more like a convenience thing that a security feature
> to prevent reuse.

That's fair. AFAIK it is not a requirement.

Allowing the host to request a key for a specific SPI will open up the
risk of requesting the same key multiple times.

The simpler device implementation of only incrementing an internal SPI
counter from 1 until ((1<<31) - 1) and then triggering a rotation
trivially avoids that risk.

But indeed this may complicate partitioning between hosts (or even PFs
and VFs) compared to explicit allocation of an SPI space partition to
each.