Re: [PATCH v3] selftests/mm: Fix UFFDIO_API usage with proper two-step feature negotiation

[David Hildenbrand <david@redhat.com>]

> Key changes:
> 
> 1. Use features=0 in the initial UFFDIO_API call to query supported
>     feature bits, rather than immediately requesting WP support.
> 
> 2. Skip the test gracefully if:
>     - UFFDIO_API fails with EINVAL (e.g. unsupported API version), or
>     - UFFD_FEATURE_PAGEFAULT_FLAG_WP is not advertised by the kernel.
> 
> 3. Close the initial userfaultfd and create a new one before enabling
>     the required feature, since UFFDIO_API can only be called once per fd.
> 
> 4. Improve diagnostics by distinguishing between expected and unexpected
>     failures, using strerror() to report errors.
> 
> This ensures the test behaves correctly across a wider range of kernel
> versions and configurations, while preserving the intended behavior on
> kernels that support UFFD-WP.
> 
> Suggestted-by: David Hildenbrand <david@redhat.com>

Skimming over this once again ... sorry.

Nit:

"Suggested-by:"

Likely Andrew can fix it up ... if the patch is not upstream yet (did 
not check).

-- 
Cheers,

David / dhildenb