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kmap_local() and related interfaces are NOOPs on 64bit and only create temporary fixmaps for highmem pages on 32bit. That means the test coverage for this code is pretty small. CONFIG_KMAP_LOCAL can be enabled independent from CONFIG_HIGHMEM, which allows to provide support for enforced kmap_local() debugging even on 64bit. For 32bit the support is unconditional, for 64bit it's only supported when CONFIG_NR_CPUS <= 4096 as supporting it for 8192 CPUs would require to set up yet another fixmap PGT. If CONFIG_KMAP_LOCAL_FORCE_DEBUG is enabled then kmap_local()/kmap_atomic() will use the temporary fixmap mapping path. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20201118204007.169209557@linutronix.de
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.