Re: [RFCv3 05/15] tcp: authopt: Add crypto initialization

[Leonard Crestez <cdleonard@gmail.com>]

On 25.08.2021 02:34, Eric Dumazet wrote:
> On 8/24/21 2:34 PM, Leonard Crestez wrote:
>> The crypto_shash API is used in order to compute packet signatures. The
>> API comes with several unfortunate limitations:
>>
>> 1) Allocating a crypto_shash can sleep and must be done in user context.
>> 2) Packet signatures must be computed in softirq context
>> 3) Packet signatures use dynamic "traffic keys" which require exclusive
>> access to crypto_shash for crypto_setkey.
>>
>> The solution is to allocate one crypto_shash for each possible cpu for
>> each algorithm at setsockopt time. The per-cpu tfm is then borrowed from
>> softirq context, signatures are computed and the tfm is returned.
>>
> 
> I could not see the per-cpu stuff that you mention in the changelog.

That's a little embarrasing, I forgot to implement the actual per-cpu 
stuff. tcp_authopt_alg_imp.tfm is meant to be an array up to NR_CPUS and 
tcp_authopt_alg_get_tfm needs no locking other than preempt_disable 
(which should already be the case).

The reference counting would still only happen from very few places: 
setsockopt, close and openreq. This would only impact request/response 
traffic and relatively little.

Performance was not a major focus so far. Preventing impact on non-AO 
connections is important but typical AO usecases are long-lived 
low-traffic connections.

--
Regards,
Leonard