netdev - Re: [PATCH xfrm-next v3 0/6] Extend XFRM core to allow full offload configuration

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Message-ID: <20220829075403.GL566407@gauss3.secunet.de>
Date:   Mon, 29 Aug 2022 09:54:03 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Leon Romanovsky <leonro@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>, Raed Salem <raeds@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH xfrm-next v3 0/6] Extend XFRM core to allow full offload
 configuration

On Tue, Aug 23, 2022 at 04:31:57PM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> Changelog:
> v3:
>  * I didn't hear any suggestion what term to use instead of
>    "full offload", so left it as is. It is used in commit messages
>    and documentation only and easy to rename.
>  * Added performance data and background info to cover letter
>  * Reused xfrm_output_resume() function to support multiple XFRM transformations
>  * Add PMTU check in addition to driver .xdo_dev_offload_ok validation
>  * Documentation is in progress, but not part of this series yet.
> v2: https://lore.kernel.org/all/cover.1660639789.git.leonro@nvidia.com
>  * Rebased to latest 6.0-rc1
>  * Add an extra check in TX datapath patch to validate packets before
>    forwarding to HW.
>  * Added policy cleanup logic in case of netdev down event
> v1: https://lore.kernel.org/all/cover.1652851393.git.leonro@nvidia.com
>  * Moved comment to be before if (...) in third patch.
> v0: https://lore.kernel.org/all/cover.1652176932.git.leonro@nvidia.com
> -----------------------------------------------------------------------
> 
> The following series extends XFRM core code to handle a new type of IPsec
> offload - full offload.
> 
> In this mode, the HW is going to be responsible for the whole data path,
> so both policy and state should be offloaded.
> 
> IPsec full offload is an improved version of IPsec crypto mode,
> In full mode, HW is responsible to trim/add headers in addition to
> decrypt/encrypt. In this mode, the packet arrives to the stack as already
> decrypted and vice versa for TX (exits to HW as not-encrypted).
> 
> Devices that implement IPsec full offload mode offload policies too.
> In the RX path, it causes the situation that HW can't effectively
> handle mixed SW and HW priorities unless users make sure that HW offloaded
> policies have higher priorities.
> 
> To make sure that users have a coherent picture, we require that
> HW offloaded policies have always (both RX and TX) higher priorities
> than SW ones.
> 
> To not over-engineer the code, HW policies are treated as SW ones and
> don't take into account netdev to allow reuse of the same priorities for
> different devices.
> 
> There are several deliberate limitations:
>  * No software fallback
>  * Fragments are dropped, both in RX and TX
>  * No sockets policies
>  * Only IPsec transport mode is implemented

... and you still have not answered the fundamental questions:

As implemented, the software does not hold any state.
I.e. there is no sync between hardware and software
regarding stats, liftetime, lifebyte, packet counts
and replay window. IKE rekeying and auditing is based
on these, how should this be done?

How can tunnel mode work with this offload?

I want to see the full picture before I consider to
apply this.