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

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Daniel Zahka wrote:
> From: Jakub Kicinski <kuba@kernel.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@kernel.org>
> Signed-off-by: Daniel Zahka <daniel.zahka@gmail.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?

> +#define PSP_TRL_SIZE	16	/* AES-GCM/GMAC trailer size */
> +
>  struct psp_skb_ext {
>  	__be32 spi;
>  	u16 dev_id;