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Date:   Fri, 4 Oct 2019 16:03:50 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     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>
Subject: Re: [PATCH v2 20/20] crypto: lib/chacha20poly1305 - reimplement
 crypt_from_sg() routine
Message-ID: <20191004140350.GC114360@zx2c4.com>
References: <20191002141713.31189-1-ard.biesheuvel@linaro.org>
 <20191002141713.31189-21-ard.biesheuvel@linaro.org>
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On Wed, Oct 02, 2019 at 04:17:13PM +0200, Ard Biesheuvel wrote:
> Reimplement the library routines to perform chacha20poly1305 en/decryption
> on scatterlists, without [ab]using the [deprecated] blkcipher interface,
> which is rather heavyweight and does things we don't really need.
> 
> Instead, we use the sg_miter API in a novel and clever way, to iterate
> over the scatterlist in-place (i.e., source == destination, which is the
> only way this library is expected to be used). That way, we don't have to
> iterate over two scatterlists in parallel.

Nice idea. Probably this will result in a real speedup, as I suspect
those extra prior kmaps weren't free. Looking forward to benching it.