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

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Date:   Mon, 17 Jul 2023 09:23:28 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     John Hubbard <jhubbard@...dia.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 15/07/2023 01:04, John Hubbard wrote:
> 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".

OK fair enough. I'll follow this approach for v2.

Thanks for the review!

> 
> 
> thanks,