netdev - Re: [PATCH v3 09/19] net: psp: update the TCP MSS to reflect PSP packet overhead

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Message-ID: <686aaf1acacc1_3b7462294aa@willemb.c.googlers.com.notmuch>
Date: Sun, 06 Jul 2025 13:15:06 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Daniel Zahka <daniel.zahka@...il.com>, 
 Donald Hunter <donald.hunter@...il.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 "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>
Cc: 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 v3 09/19] net: psp: update the TCP MSS to reflect PSP
 packet overhead

Willem de Bruijn wrote:
> Daniel Zahka wrote:
> > From: Jakub Kicinski <kuba@...nel.org>
> > 
> > PSP eats 32B of header space. Adjust MSS appropriately.
> > 
> > We can either modify tcp_mtu_to_mss() / tcp_mss_to_mtu()
> > or reuse icsk_ext_hdr_len. The former option is more TCP
> > specific and has runtime overhead. The latter is a bit
> > of a hack as PSP is not an ext_hdr. If one squints hard
> > enough, UDP encap is just a more practical version of
> > IPv6 exthdr, so go with the latter. Happy to change.
> > 
> > Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> > Signed-off-by: Daniel Zahka <daniel.zahka@...il.com>
> > ---
> > 
> > Notes:
> >     v1:
> >     - https://lore.kernel.org/netdev/20240510030435.120935-8-kuba@kernel.org/
> > 
> >  include/net/psp/functions.h | 12 ++++++++++++
> >  include/net/psp/types.h     |  3 +++
> >  net/ipv4/tcp_ipv4.c         |  4 ++--
> >  net/ipv6/ipv6_sockglue.c    |  6 +++++-
> >  net/ipv6/tcp_ipv6.c         |  6 +++---
> >  net/psp/psp_sock.c          |  5 +++++
> >  6 files changed, 30 insertions(+), 6 deletions(-)
> > 
> 
> > @@ -95,6 +95,9 @@ struct psp_dev_caps {
> >  #define PSP_V1_KEY	32
> >  #define PSP_MAX_KEY	32
> >  
> > +#define PSP_HDR_SIZE	16	/* We don't support optional fields, yet */
> 
> Duplicate of PSP_HDRLEN_NOOPT?

Oh no it is not: that is the length in 64b words.