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Next commits will introduce vendor-specific CPUID ranges like Transmeta's 0x8086000 range and Centaur's 0xc0000000. Initially explicit vendor detection was implemented, but it turned out to be not strictly necessary. As Dave Hansen noted, even established tools like cpuid(1) just tries all ranges indices, and see if the CPU responds back with something sensible. Do something similar at setup_cpuid_range(). Query the range's index, and check the maximum range function value returned. If it's within an expected interval of [range_index, range_index + MAX_RANGE_INDEX_OFFSET], accept the range as valid and further query its leaves. Set MAX_RANGE_INDEX_OFFSET to a heuristic of 0xff. That should be sensible enough since all the ranges covered by x86-cpuid-db XML database are: 0x00000000 0x00000023 0x40000000 0x40000000 0x80000000 0x80000026 0x80860000 0x80860007 0xc0000000 0xc0000001 At setup_cpuid_range(), if the range's returned maximum function was not sane, mark it as invalid by setting its number of leaves, range->nr, to zero. Introduce the for_each_valid_cpuid_range() iterator instead of sprinkling "range->nr != 0" checks throughout the code. Suggested-by: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lore.kernel.org/r/20250324142042.29010-15-darwi@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 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.