linux-kernel - Re: [PATCH v1 3/9] selftests/mm: Skip soft-dirty tests on arm64

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Date:   Fri, 14 Jul 2023 17:04:19 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Mark Brown <broonie@...nel.org>,
        Florent Revest <revest@...omium.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v1 3/9] selftests/mm: Skip soft-dirty tests on arm64

On 7/13/23 06:54, Ryan Roberts wrote:
> arm64 does not support the soft-dirty PTE bit. However there are tests
> in `madv_populate` and `soft-dirty` which assume it is supported and
> cause spurious failures to be reported when preferred behaviour would be
> to mark the tests as skipped.
> 
> Unfortunately, the only way to determine if the soft-dirty dirty bit is
> supported is to write to a page, then see if the bit is set in
> /proc/self/pagemap. But the tests that we want to conditionally execute
> are testing precicesly this. So if we introduced this feature check, we
> could accedentally turn a real failure (on a system that claims to
> support soft-dirty) into a skip.

...

> diff --git a/tools/testing/selftests/mm/soft-dirty.c b/tools/testing/selftests/mm/soft-dirty.c
> index cc5f144430d4..8a2cd161ec4d 100644
> --- a/tools/testing/selftests/mm/soft-dirty.c
> +++ b/tools/testing/selftests/mm/soft-dirty.c

Hi Ryan,

Probably very similar to what David is requesting: given that arm64
definitively does not support soft dirty, I'd suggest that we not even
*build* the soft dirty tests on arm64!

There is no need to worry about counting, skipping or waiving such
tests, either. Because it's just a non-issue: one does not care about
test status for something that is documented as "this feature is simply
unavailable here".


thanks,
-- 
John Hubbard
NVIDIA