Re: [PATCH] selftests/mm: Fix soft-dirty kselftest supported check

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 20 Mar 2026 14:39:15 -0400 Audra Mitchell <audra@redhat.com> wrote:

> On architectures with separate user address space, such as s390 or
> those without an MMU, the soft-dirty kselftest may fail when checking
> to see if the feature is supported.
> 
>   # --------------------
>   # running ./soft-dirty
>   # --------------------
>   # TAP version 13
>   # 1..15
>   # Bail out! PAGEMAP_SCAN succeeded unexpectedly
>   # # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
>   # [FAIL]
>   not ok 1 soft-dirty # exit=1
>   # SUMMARY: PASS=0 SKIP=0 FAIL=1
> 
> The soft-dirty test will initate an ioctl with the PAGEMAP_SCAN flag with
> an invalid address for the page_region. This is done intentionally to
> have the ioctl return with an expected EFAULT and with the correct
> categories returned.
> 
> However, on architectures with separate user address space, such as s390 or
> those without an MMU, the call to __access_ok (used to validate the
> variables provided with the ioctl) will always return true and we will not
> fail as expected.
> 
>         if (IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE) ||
>             !IS_ENABLED(CONFIG_MMU))
>                 return true;
> 
> Let's simplify the check for PAGEMAP_SCAN and provide a valid page_region
> address so that we get a non-errno return if it is supported.

AI review asked some questions about v1:
	https://sashiko.dev/#/patchset/20260320184010.759461-2-audra%40redhat.com

These might have been addressed in this version but without a
versioning tag and without a what-i-changed description I find it
hard(er) to tell.