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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Fri, 4 Oct 2019 16:38:01 +0200
Message-ID: <CAKv+Gu_X9DBgUiPqcyJ2hOQqi_FEBVpHOr9uG1ZAh-RWv6-z9Q@mail.gmail.com>
Subject: Re: [PATCH v2 05/20] crypto: mips/chacha - import accelerated 32r2
 code from Zinc
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Miller <davem@davemloft.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Samuel Neves <sneves@dei.uc.pt>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Eric Biggers <ebiggers@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Martin Willi <martin@strongswan.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        =?UTF-8?Q?Ren=C3=A9_van_Dorst?= <opensource@vdorst.com>
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On Fri, 4 Oct 2019 at 15:46, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> On Wed, Oct 02, 2019 at 04:16:58PM +0200, Ard Biesheuvel wrote:
> > This integrates the accelerated MIPS 32r2 implementation of ChaCha
> > into both the API and library interfaces of the kernel crypto stack.
> >
> > The significance of this is that, in addition to becoming available
> > as an accelerated library implementation, it can also be used by
> > existing crypto API code such as Adiantum (for block encryption on
> > ultra low performance cores) or IPsec using chacha20poly1305. These
> > are use cases that have already opted into using the abstract crypto
> > API. In order to support Adiantum, the core assembler routine has
> > been adapted to take the round count as a function argument rather
> > than hardcoding it to 20.
>
> Could you resubmit this with first my original commit and then with your
> changes on top? I'd like to see and be able to review exactly what's
> changed. If I recall correctly, Ren=C3=A9 and I were really starved for
> registers and tried pretty hard to avoid spilling to the stack, so I'm
> interested to learn how you crammed a bit more sauce in there.
>

The round count is passed via the fifth function parameter, so it is
already on the stack. Reloading it for every block doesn't sound like
a huge deal to me.

> I also wonder if maybe it'd be better to just leave this as is with 20
> rounds, which it was previously optimized for, and just not do
> accelerated Adiantum for MIPS. Android has long since given up on the
> ISA entirely.

Adiantum does not depend on Android - anyone running linux on his MIPS
router can use it if they want encrypted storage.