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We currently insist on disabling PAuth on vcpu_load(), and get to enable it on first guest use of an instruction or a key (ignoring the NV case for now). It isn't clear at all what this is trying to achieve: guests tend to use PAuth when available, and nothing forces you to expose it to the guest if you don't want to. This also isn't totally free: we take a full GPR save/restore between host and guest, only to write ten 64bit registers. The "value proposition" escapes me. So let's forget this stuff and enable PAuth eagerly if exposed to the guest. This results in much simpler code. Performance wise, that's not bad either (tested on M2 Pro running a fully automated Debian installer as the workload): - On a non-NV guest, I can see reduction of 0.24% in the number of cycles (measured with perf over 10 consecutive runs) - On a NV guest (L2), I see a 2% reduction in wall-clock time (measured with 'time', as M2 doesn't have a PMUv3 and NV doesn't support it either) So overall, a much reduced complexity and a (small) performance improvement. Reviewed-by: Oliver Upton <oliver.upton@linux.dev> Link: https://lore.kernel.org/r/20240419102935.1935571-16-maz@kernel.org Signed-off-by: Marc Zyngier <maz@kernel.org>
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 reStructuredText 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.