[PATCH v5 0/5] x86/cpufeatures: Automatically generate required and disabled feature masks

[Xin Li (Intel)]

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@xxxxxxxxx/.
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@xxxxxxx/.
https://lore.kernel.org/all/20240126041126.1927228-23-michael.roth@xxxxxxx/.

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@xxxxxxxx/.

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.

Recently when working on the immediate form of MSR access instructions,
I needed to add a new CPU feature word for CPUID.7.1.ECX, and I had to
replace the same check "(NCAPINTS != 22)" with (NCAPINTS != 23) in 3
different files as
https://github.com/xinli-intel/linux-fred-public/commit/aa80536927fcd293be8ae54e1d5e4d886cf83f21
Obviously these replacements could be saved if the patch to add a new
CPU feature word is reworked on top of this patch set.

So this seems a good opportunity to demonstrate the convenience out of
this patch set, and here comes v5 with just one more patch on top of v4
that adds a new CPU feature word for CPUID.7.1.ECX and uses it for the
immediate form of MSR access feature.

Link to v4:
https://lore.kernel.org/lkml/20240628174544.3118826-1-xin@xxxxxxxxx/


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) (3):
  x86/cpufeatures: Remove {disabled,required}-features.h
  x86/cpufeatures: Use AWK to generate {REQUIRED|DISABLED}_MASK_BIT_SET
  x86/cpufeatures: Add the CPU feature bit for MSR immediate form
    instructions

 arch/x86/Kconfig                              |   4 +-
 arch/x86/Kconfig.cpu                          |  12 +-
 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/bitops.h                 |   4 +-
 arch/x86/include/asm/cmpxchg_32.h             |   2 +-
 arch/x86/include/asm/cpufeature.h             |  71 +------
 arch/x86/include/asm/cpufeatures.h            |  13 +-
 arch/x86/include/asm/disabled-features.h      | 161 --------------
 arch/x86/include/asm/required-features.h      | 105 ----------
 arch/x86/kernel/cpu/common.c                  |   1 +
 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 -
 26 files changed, 327 insertions(+), 646 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: af2c8596bd2e455ae350ba1585bc938ee85aa38d
-- 
2.47.1