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

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Message-ID: <20250106070727.3211006-1-xin@zytor.com>
Date: Sun,  5 Jan 2025 23:07:22 -0800
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        will@...nel.org, peterz@...radead.org, yury.norov@...il.com,
        akpm@...ux-foundation.org, acme@...nel.org, namhyung@...nel.org,
        brgerst@...il.com, andrew.cooper3@...rix.com, nik.borisov@...e.com
Subject: [PATCH v5 0/5] x86/cpufeatures: Automatically generate required and disabled feature masks

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.

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@zytor.com/

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