netdev - RE: [PATCH net-next 5/5] tls: Add generic NIC offload infrastructure.

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Date:   Tue, 19 Sep 2017 07:36:28 +0000
From:   Ilya Lesokhin <ilyal@...lanox.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "davejwatson@...com" <davejwatson@...com>,
        "tom@...bertland.com" <tom@...bertland.com>,
        Boris Pismenny <borisp@...lanox.com>,
        Aviad Yehezkel <aviadye@...lanox.com>,
        Liran Liss <liranl@...lanox.com>
Subject: RE: [PATCH net-next 5/5] tls: Add generic NIC offload infrastructure.

Hannes Frederic Sowa <hannes@...essinduktion.org> writes:

> The user should be aware of that they can't migrate the socket to another
> interface if they got hw offloaded. This is not the case for software offload.
> Thus I think the user has to opt in and it shouldn't be a heuristic until we can
> switch back to sw offload path.
> 
> Maybe change flowi_oif to sk_bound_dev_if and somwhow lock it against
> further changes if hw tls is in use?
> 

I'm not sure I follow.
We do set sk->sk_bound_dev_if to prevent further changes.

Do you recommend we enable TLS offload only if SO_BINDTODEVICE	
was previously used on that socket?
and prevent even users with CAP_NET_RAW from unbinding it?

I would rather avoid requiring CAP_NET_RAW to use TLS offload. 
But admittedly I'm not sure setting sk->sk_bound_dev_if 
without CAP_NET_RAW like we do is legit either.

Finally, the reason we made HW offload the default is that the user
can use sudo ethtool -K enp0s4 tls-hw-tx-offload off to opt out of HW offload
and we currently don't have anything equivalent for opting out of SW KTLS.

Thanks,
Ilya