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

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Date:   Wed, 25 Aug 2021 10:55:49 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Leonard Crestez <cdleonard@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        David Ahern <dsahern@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Ivan Delalande <colona@...sta.com>,
        Priyaranjan Jha <priyarjha@...gle.com>,
        Menglong Dong <dong.menglong@....com.cn>,
        netdev <netdev@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [RFCv3 05/15] tcp: authopt: Add crypto initialization

On Wed, Aug 25, 2021 at 9:35 AM Leonard Crestez <cdleonard@...il.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:
> >>
> >> 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).

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