It turns out the code to generate the x86 cpufeaturemasks.h header was way too aggressive, and would re-generate it whenever the timestamp on the kernel config file changed. Now, the regular 'make *config' tools are fairly careful to not rewrite the kernel config file unless the contents change, but other usecases aren't that careful. Michael Kelley reports that 'make-kpkg' ends up doing "make syncconfig" multiple times in prepping to build, and will modify the config file in the process (and then modify it back, but by then the timestamps have changed). Jakub Kicinski reports that the netdev CI does something similar in how it generates the config file in multiple steps. In both cases, the config file timestamp updates then cause the cpufeaturemasks.h file to be regenerated, and that in turn then causes lots of unnecessary rebuilds due to all the normal dependencies. Fix it by using our 'filechk' infrastructure in the Makefile to generate the header file. That will only write a new version of the file if the contents of the file have actually changed. Fixes: 841326332bcb ("x86/cpufeatures: Generate the <asm/cpufeaturemasks.h> header based on build config") Reported-by: Michael Kelley <mhklinux@outlook.com> Reported-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/all/SN6PR02MB415756D1829740F6E8AC11D1D4D82@SN6PR02MB4157.namprd02.prod.outlook.com/ Link: https://lore.kernel.org/all/20250328162311.08134fa6@kernel.org/ Cc: Peter Anvin <hpa@zytor.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>