On Wed, Aug 25, 2021 at 9:35 AM Leonard Crestez cdleonard@gmail.com wrote:
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:
- Allocating a crypto_shash can sleep and must be done in user context.
- Packet signatures must be computed in softirq context
- 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).
Well, do not use arrays of NR_CPUS and instead use normal per_cpu accessors (as in __tcp_alloc_md5sig_pool)
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.
What I meant is that __tcp_alloc_md5sig_pool() allocates stuff one time, we do not care about tcp_md5sig_pool_populated going back to false.
Otherwise, a single user application constantly allocating a socket, enabling MD5 (or authopt), then closing the socket would incur a big cost on hosts with a lot of cpus.
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