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Counter mode is a stream cipher chaining mode that is typically used with inputs that are of arbitrarily length, and so a tail block which is smaller than a full AES block is rule rather than exception. The current ctr(aes) implementation for arm64 always makes a separate call into the assembler routine to process this tail block, which is suboptimal, given that it requires reloading of the AES round keys, and prevents us from handling this tail block using the 5-way stride that we use for better performance on deep pipelines. So let's update the assembler routine so it can handle any input size, and uses NEON permutation instructions and overlapping loads and stores to handle the tail block. This results in a ~16% speedup for 1420 byte blocks on cores with deep pipelines such as ThunderX2. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.