[PATCH v3 0/4] x86/cpufeatures: Automatically generate required and disabled feature masks

From: Xin Li (Intel)
Date: Sat Jun 22 2024 - 13:15:28 EST


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.


Changes since v2:
* Remove AWK code that generates extra debugging comments (Brian Gerst).
* Move SSE_MASK to verify_cpu.S, the only place it is used (Brian Gerst).
* Add a patch to generate macros {REQUIRED|DISABLED}_MASK_BIT_SET in the
new AWK script (Brian Gerst).

Changes since v1:
* Keep the X86_{REQUIRED,DISABLED}_FEATURE_ prefixes solely in
arch/x86/Kconfig.cpufeatures (Borislav Petkov).
* Explain how config option names X86_{REQUIRED,DISABLED}_FEATURE_<name>
are formed (Borislav Petkov).
* Remove code generating unused macros {REQUIRED,DISABLED}_FEATURE(x)
to tell if a CPU feature, e.g., X86_FEATURE_FRED, is a required or
disabled feature for this particular compile-time configuration.


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 | 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 | 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 | 94 +++++++++
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 -
25 files changed, 327 insertions(+), 645 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: aedd5b6d65f7db9af616404985fc8361373690be
--
2.45.2