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The cpu_spec is a struct holding various information about the CPU the kernel is executing on. It's populated early in boot and must not change after that. In particular the cpu_features and mmu_features hold the set of discovered CPU/MMU features and are used to set static keys for each feature, and do binary patching of assembly. So any change to the cpu_features/mmu_features later in boot will not be reflected in the state of the static keys or patched code. There is already logic to check that cpu_features/mmu_features don't change, see check_features() in feature-fixups.c. But as another layer of protection the entire cpu_spec should be read only after init, annotate it as such. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231025012452.1985680-1-mpe@ellerman.id.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.