From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [PATCH net-next v6 07/23] zinc: ChaCha20 ARM and ARM64 implementations
Date: Wed, 26 Sep 2018 17:51:47 +0200
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Cc: Herbert Xu <herbert@gondor.apana.org.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "<netdev@vger.kernel.org>" <netdev@vger.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Samuel Neves <sneves@dei.uc.pt>,
        Andy Lutomirski <luto@kernel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
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On Wed, 26 Sep 2018 at 17:50, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> On Wed, Sep 26, 2018 at 5:45 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> > So what you have in mind is something like calling simd_relax() every
> > 4096 bytes or so?
>
> That was actually pretty easy, putting together both of your suggestions:
>
> static inline bool chacha20_arch(struct chacha20_ctx *state, u8 *dst,
>                  u8 *src, size_t len,
>                  simd_context_t *simd_context)
> {
>     while (len > PAGE_SIZE) {
>         chacha20_arch(state, dst, src, PAGE_SIZE, simd_context);
>         len -= PAGE_SIZE;
>         src += PAGE_SIZE;
>         dst += PAGE_SIZE;
>         simd_relax(simd_context);
>     }
>     if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) && chacha20_use_neon &&
>         len >= CHACHA20_BLOCK_SIZE * 3 && simd_use(simd_context))
>         chacha20_neon(dst, src, len, state->key, state->counter);
>     else
>         chacha20_arm(dst, src, len, state->key, state->counter);
>
>     state->counter[0] += (len + 63) / 64;
>     return true;
> }

Nice one :-)

This works for me (but perhaps add a comment as well)