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 v5:
https://lore.kernel.org/lkml/20250106070727.3211006-1-xin@zytor.com/


H. Peter Anvin (Intel) (3):
  x86/cpufeatures: Rename X86_CMPXCHG64 to X86_CX8
  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                              |   4 +-
 arch/x86/Kconfig.cpu                          |   4 +-
 arch/x86/Kconfig.cpufeatures                  | 197 ++++++++++++++++++
 arch/x86/Makefile                             |  17 +-
 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/asm-prototypes.h         |   2 +-
 arch/x86/include/asm/atomic64_32.h            |   2 +-
 arch/x86/include/asm/cmpxchg_32.h             |   2 +-
 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/lib/Makefile                         |   2 +-
 arch/x86/lib/cmpxchg8b_emu.S                  |   2 +-
 arch/x86/tools/featuremasks.awk               |  88 ++++++++
 lib/atomic64_test.c                           |   2 +-
 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 -
 24 files changed, 320 insertions(+), 634 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: 0b8c04b9207d5ee92ab3b341f0211aaf2c0b6976
-- 
2.48.1

* Xin Li (Intel) <xin@zytor.com> 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 v5:
> https://lore.kernel.org/lkml/20250106070727.3211006-1-xin@zytor.com/
> 
> 
> H. Peter Anvin (Intel) (3):
>   x86/cpufeatures: Rename X86_CMPXCHG64 to X86_CX8
>   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

>  24 files changed, 320 insertions(+), 634 deletions(-)

Very nice!

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo