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.
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) (1):
x86/cpufeatures: Remove {disabled,required}-features.h
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 | 1 +
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 | 1 +
arch/x86/lib/Makefile | 2 +-
arch/x86/lib/cmpxchg8b_emu.S | 2 +-
arch/x86/tools/featuremasks.awk | 90 ++++++++
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, 320 insertions(+), 576 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: 49b33979e3bf0a5424420d14f026de12f34e8b1e
--
2.45.1