On 3/5/2025 10:47 AM, Xin Li (Intel) wrote:
> The x86 build process first generates required and disabled feature
> masks based on current build config, and then uses these generated
> masks to compile the source code. When a CPU feature is not enabled
> in a build config, e.g., when CONFIG_X86_FRED=n, its feature disable
> flag, i.e., DISABLE_FRED, needs to be properly defined and added to
> a specific disabled CPU features mask in <asm/disabled-features.h>,
> as the following patch does:
> https://lore.kernel.org/all/20231205105030.8698-8-xin3.li@intel.com/.
> As a result, the FRED feature bit is surely cleared in the generated
> kernel binary when CONFIG_X86_FRED=n.
>
> Recently there is another case to repeat the same exercise for the
> AMD SEV-SNP CPU feature:
> https://lore.kernel.org/all/20240126041126.1927228-2-michael.roth@amd.com/.
> https://lore.kernel.org/all/20240126041126.1927228-23-michael.roth@amd.com/.
>
> It was one thing when there were four of CPU feature masks, but with
> over 20 it is going to cause mistakes, e.g.,
> https://lore.kernel.org/lkml/aaed79d5-d683-d1bc-7ba1-b33c8d6db618@suse.com/.
>
> We want to eliminate the stupidly repeated exercise to manually assign
> features to CPU feature words through introducing an AWK script to
> automatically generate a header with required and disabled CPU feature
> masks based on current build config, and this patch set does that.
>
> Link to v6:
> https://lore.kernel.org/lkml/20250228082338.73859-1-xin@zytor.com/
>
> Changes in v7:
> * Fix build error with "make distclean; make headers" (Aithal, Srikanth)
> * Collect reviewed-bys.
>
This version v7 can be cleanly applied on tip/x86/cpu but NOT the latest
tip/master.
I guess I don't have to rebase on the latest tip/master and resend it?
Thanks!
Xin
>
> H. Peter Anvin (Intel) (2):
> x86/cpufeatures: Add {required,disabled} feature configs
> x86/cpufeatures: Generate a feature mask header based on build config
>
> Xin Li (Intel) (2):
> x86/cpufeatures: Remove {disabled,required}-features.h
> x86/cpufeatures: Use AWK to generate {REQUIRED|DISABLED}_MASK_BIT_SET
>
> arch/x86/Kconfig | 2 +
> arch/x86/Kconfig.cpufeatures | 197 ++++++++++++++++++
> arch/x86/Makefile | 15 ++
> arch/x86/boot/cpucheck.c | 3 +-
> arch/x86/boot/cpuflags.c | 1 -
> arch/x86/boot/mkcpustr.c | 3 +-
> arch/x86/include/asm/Kbuild | 1 +
> arch/x86/include/asm/cpufeature.h | 70 +------
> arch/x86/include/asm/cpufeatures.h | 8 -
> arch/x86/include/asm/disabled-features.h | 161 --------------
> arch/x86/include/asm/required-features.h | 105 ----------
> arch/x86/kernel/verify_cpu.S | 4 +
> arch/x86/tools/featuremasks.awk | 88 ++++++++
> tools/arch/x86/include/asm/cpufeatures.h | 8 -
> .../arch/x86/include/asm/disabled-features.h | 161 --------------
> .../arch/x86/include/asm/required-features.h | 105 ----------
> tools/perf/check-headers.sh | 2 -
> 17 files changed, 311 insertions(+), 623 deletions(-)
> create mode 100644 arch/x86/Kconfig.cpufeatures
> delete mode 100644 arch/x86/include/asm/disabled-features.h
> delete mode 100644 arch/x86/include/asm/required-features.h
> create mode 100755 arch/x86/tools/featuremasks.awk
> delete mode 100644 tools/arch/x86/include/asm/disabled-features.h
> delete mode 100644 tools/arch/x86/include/asm/required-features.h
>
>
> base-commit: 32dc26a2f55f71907af0874468298c6ab8a8f7f9