Re: [PATCH v6 2/5] x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag

["Huang, Kai" <kai.huang@intel.com>]

On Thu, 2025-05-22 at 12:21 +0300, Elena Reshetova wrote:
> --- a/tools/arch/x86/include/asm/cpufeatures.h
> +++ b/tools/arch/x86/include/asm/cpufeatures.h
> @@ -481,6 +481,7 @@
>  #define X86_FEATURE_AMD_HTR_CORES	(21*32+ 6) /* Heterogeneous Core Topology */
>  #define X86_FEATURE_AMD_WORKLOAD_CLASS	(21*32+ 7) /* Workload Classification */
>  #define X86_FEATURE_PREFER_YMM		(21*32+ 8) /* Avoid ZMM registers due to downclocking */
> +#define X86_FEATURE_SGX_EUPDATESVN	(21*32+11) /* Support for ENCLS[EUPDATESVN] instruction */

[Sorry for not mentioning in the previous version.]

Nit:

I am not sure we need to change tool headers.

Per commit

  f6d9883f8e68 ("tools/include: Sync x86 headers with the kernel sources")

.. and tools/include/uapi/README:

  ...

  What we are doing now is a third option:

   - A software-enforced copy-on-write mechanism of kernel headers to
     tooling, driven by non-fatal warnings on the tooling side build when
     kernel headers get modified:

      Warning: Kernel ABI header differences:
        diff -u tools/include/uapi/drm/i915_drm.h include/uapi/drm/i915_drm.h
        diff -u tools/include/uapi/linux/fs.h include/uapi/linux/fs.h
        diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h
        ...

     The tooling policy is to always pick up the kernel side headers as-is,
     and integate them into the tooling build. The warnings above serve as a
     notification to tooling maintainers that there's changes on the kernel
     side.

  We've been using this for many years now, and it might seem hacky, but
  works surprisingly well.

.. I interpret the updating to tools headers is not mandatory (unless building
tools fails w/o the new feature bit definition which I believe isn't the case of
SGX_UPDATESVN).  The tools maintainers will eventually do the sync.

But on the other hand, modifying tools headers in this patch also reduces tools
maintainer's effort in the future.

That being said, I am unclear with the rule here.  Perhaps Dave/Ingo can help to
clarify.