linux-kernel - Re: [PATCH v5 5/5] selftests/mm: add UFFDIO

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Message-ID: <CAJuCfpH8-jsxBRiLeLGWOFYnFE2iuSPfsveZkRf=MYZ6d=G7QA@mail.gmail.com>
Date:   Fri, 1 Dec 2023 08:26:51 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Ryan Roberts <ryan.roberts@....com>
Cc:     akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
        brauner@...nel.org, shuah@...nel.org, aarcange@...hat.com,
        lokeshgidra@...gle.com, peterx@...hat.com, david@...hat.com,
        hughd@...gle.com, mhocko@...e.com, axelrasmussen@...gle.com,
        rppt@...nel.org, willy@...radead.org, Liam.Howlett@...cle.com,
        jannh@...gle.com, zhangpeng362@...wei.com, bgeffon@...gle.com,
        kaleshsingh@...gle.com, ngeoffray@...gle.com, jdduke@...gle.com,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v5 5/5] selftests/mm: add UFFDIO_MOVE ioctl test

On Fri, Dec 1, 2023 at 1:29 AM Ryan Roberts <ryan.roberts@....com> wrote:
>
> On 21/11/2023 17:16, Suren Baghdasaryan wrote:
> > Add tests for new UFFDIO_MOVE ioctl which uses uffd to move source
> > into destination buffer while checking the contents of both after
> > the move. After the operation the content of the destination buffer
> > should match the original source buffer's content while the source
> > buffer should be zeroed. Separate tests are designed for PMD aligned and
> > unaligned cases because they utilize different code paths in the kernel.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  tools/testing/selftests/mm/uffd-common.c     |  24 +++
> >  tools/testing/selftests/mm/uffd-common.h     |   1 +
> >  tools/testing/selftests/mm/uffd-unit-tests.c | 189 +++++++++++++++++++
> >  3 files changed, 214 insertions(+)
> >
> > diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
> > index fb3bbc77fd00..b0ac0ec2356d 100644
> > --- a/tools/testing/selftests/mm/uffd-common.c
> > +++ b/tools/testing/selftests/mm/uffd-common.c
> > @@ -631,6 +631,30 @@ int copy_page(int ufd, unsigned long offset, bool wp)
> >       return __copy_page(ufd, offset, false, wp);
> >  }
> >
> > +int move_page(int ufd, unsigned long offset, unsigned long len)
> > +{
> > +     struct uffdio_move uffdio_move;
> > +
> > +     if (offset + len > nr_pages * page_size)
> > +             err("unexpected offset %lu and length %lu\n", offset, len);
> > +     uffdio_move.dst = (unsigned long) area_dst + offset;
> > +     uffdio_move.src = (unsigned long) area_src + offset;
> > +     uffdio_move.len = len;
> > +     uffdio_move.mode = UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
> > +     uffdio_move.move = 0;
> > +     if (ioctl(ufd, UFFDIO_MOVE, &uffdio_move)) {
> > +             /* real retval in uffdio_move.move */
> > +             if (uffdio_move.move != -EEXIST)
> > +                     err("UFFDIO_MOVE error: %"PRId64,
> > +                         (int64_t)uffdio_move.move);
>
> Hi Suren,
>
> FYI this error is triggering in mm-unstable (715b67adf4c8):
>
> Testing move-pmd on anon... ERROR: UFFDIO_MOVE error: -16 (errno=16,
> @uffd-common.c:648)
>
> I'm running in a VM on Apple M2 (arm64). I haven't debugged any further, but
> happy to go deeper if you can direct.

Hi Ryan,
Thanks for reporting! Could you please share your kernel config file?

There are several places UFFDIO_MOVE returns EBUSY: 4 places in
move_pages_huge_pmd(), 2 places in move_present_pte(), 2 places in
move_pages_pte() and once in move_swap_pte(). While I'm trying to
reproduce, it would be useful if you could check which place is
triggering the error.
Thanks,
Suren.

>
> Thanks,
> Ryan
>
>
> > +             wake_range(ufd, uffdio_move.dst, len);
> > +     } else if (uffdio_move.move != len) {
> > +             err("UFFDIO_MOVE error: %"PRId64, (int64_t)uffdio_move.move);
> > +     } else
> > +             return 1;
> > +     return 0;
> > +}
>
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