Re: [PATCH v4 0/4] x86/cpufeatures: Automatically generate required and disabled feature masks

[Xin Li]

On 8/19/2024 11:25 PM, Xin Li wrote:
> On 6/28/2024 10:45 AM, Xin Li (Intel) 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@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.
> >
> > Link to v3:
> > https://lore.kernel.org/lkml/20240622171435.3725548-1-xin@xxxxxxxxx/
> >
> > Changes since v3:
> > * Add a few high-level comments to the AWK script (Nikolay Borisov).
> > * Use '1U' instead of '1' in feature mask shifting (Andrew Cooper).
> > * Checking NCAPINTS isn't necessary anymore.  It was needed when these
> >    macros had to be manually updated, but now if cpufeatures.h changes
> >    this header will be regenerated (Brian Gerst).
> > * Enforce CPU feature mask values to be unsigned.
> >
> > 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.
>
> A gentle ping...

Another ping!