net: psp: update the TCP MSS to reflect PSP packet overhead

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PSP eats 40B 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.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250917000954.859376-10-daniel.zahka@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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This commit is contained in:

Jakub Kicinski 2025-09-16 17:09:36 -07:00 • committed by Paolo Abeni

parent 6b46ca260e

commit e97269257f

6 changed files with 32 additions and 6 deletions

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14

include/net/psp/functions.h

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3

include/net/psp/types.h

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4

net/ipv4/tcp_ipv4.c

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6

net/ipv6/ipv6_sockglue.c

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6

net/ipv6/tcp_ipv6.c

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5

net/psp/psp_sock.c

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