netdev - Re: [PATCH net 3/3] Documentation: add TLS offload documentation

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Date:   Thu, 16 May 2019 11:13:47 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Boris Pismenny <borisp@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>,
        "davejwatson@...com" <davejwatson@...com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "vakul.garg@....com" <vakul.garg@....com>,
        Alexei Starovoitov <ast@...nel.org>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH net 3/3] Documentation: add TLS offload documentation

On Thu, May 16, 2019 at 10:57 AM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
>   The preferred method of reporting the Layer 4 (TCP) checksum offload
>   for packets decrypted by the device is to update the checksum field
>   to the correct value for clear text and report CHECKSUM_UNNECESSARY
>   or CHECKSUM_COMPLETE computed over clear text. However, the exact
>   semantics of RX checksum offload when NIC performs data modification
>   are not clear and subject to change.

when host is consuming the tcp stream I don't see the value of
tcp checksum on top tls.
In that sense CHECKSUM_UNNECESSARY is fine and no
need to update checksum field.
Even in case of sockmap and tcp stream redirect it is still fine.
Only the tcp payload being redirected to a different tcp socket
and the headers are gone.
So imo in all cases CHECKSUM_UNNECESSARY is fine
even without adjustment to checksum field.

Obviously the hw/firmware should have checked tcp csum before doing decrypt.