linux-kernel - Re: [PATCH] selftests/mm: pass filename as input param to VM

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Message-ID: <CAA9mObBMtE=w=PS8NpXsrHD5rs51pkDAA55Fi1dB0gCXwL9n+Q@mail.gmail.com>
Date: Fri, 1 Aug 2025 16:46:54 -0700
From: Sudarsan Mahendran <sudarsanm@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kselftest@...r.kernel.org, Shuah Khan <shuah@...nel.org>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	trivial@...nel.org
Subject: Re: [PATCH] selftests/mm: pass filename as input param to VM_PFNMAP tests

Thanks for the review!
I've sent a follow up v2 patch.


On Fri, Aug 1, 2025 at 12:15 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 31.07.25 22:10, Sudarsan Mahendran wrote:
> > Enable these tests to be run on other pfnmap'ed memory like
> > NVIDIA's EGM.
> >
> > Add '--' as a separator to pass in file path. This allows
> > passing of cmd line arguments to kselftest_harness.
> > Use '/dev/mem' as default filename.
> >
> > Existing test passes:
> >       pfnmap
> >       TAP version 13
> >       1..6
> >       # Starting 6 tests from 1 test cases.
> >       # PASSED: 6 / 6 tests passed.
> >       # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
> >
> > Pass params to kselftest_harness:
> >       pfnmap -r pfnmap:mremap_fixed
> >       TAP version 13
> >       1..1
> >       # Starting 1 tests from 1 test cases.
> >       #  RUN           pfnmap.mremap_fixed ...
> >       #            OK  pfnmap.mremap_fixed
> >       ok 1 pfnmap.mremap_fixed
> >       # PASSED: 1 / 1 tests passed.
> >       # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
> >
> > Pass random file name as input:
> >       pfnmap -- /dev/blah
> >       TAP version 13
> >       1..6
> >       # Starting 6 tests from 1 test cases.
> >       #  RUN           pfnmap.madvise_disallowed ...
> >       #      SKIP      Cannot open '/dev/blah'
>
> Now, if you really just pass a random *actual file* that exists, the
> test case will not actually test what we want.
>
> Unless you have a way to verify that you actually get a PFNMAP mapping,
> this extension is questionable. It will make the test report possibly
> wrong results when wrong files are provided.
>
> I think we can test whether we get a PFNMAP mapping by looking at the
> flags in smaps output ("pf" in flags), so I would expect such a test to
> be done in pfnmap, and the test should FAIL if the file would not create
> a PFNMAP.
>
>
> But more importantly, we rely on "/proc/iomem" to find a RAM target in
> /dev/mem. That doesn't make any sense with what you are doing here.
>
> If we are not provided /dev/mem, you should probably try mapping offset
> 0 of the file.
>
> --
> Cheers,
>
> David / dhildenb
>