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

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Date:   Tue, 24 Aug 2021 16:02:32 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Leonard Crestez <cdleonard@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        David Ahern <dsahern@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "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@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFCv3 05/15] tcp: authopt: Add crypto initialization



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.
> 
> The pool for each algorithm is reference counted, initialized at
> setsockopt time and released in tcp_authopt_key_info's rcu callback
> 
>

I don't know, why should we really care and try so hard to release
the tfm per cpu ?

I would simply allocate them at boot time.
This would avoid the expensive refcounting (potential false sharing)