Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
MIME-Version: 1.0
References: <20231121171643.3719880-1-surenb@google.com> <20231121171643.3719880-6-surenb@google.com>
 <b3c882d2-0135-430c-8179-784f78be0902@arm.com> <a41c759f-78d8-44ed-b708-1bb737a8e6c1@redhat.com>
 <cb3d3b12-abf3-4eda-8d9a-944684d05505@arm.com> <ccdb1080-7a2e-4f98-a4e8-e864fa2db299@redhat.com>
 <CAJuCfpHS63bXkRGE1_G4z-2fDe72BeLka8t5ioSg2OXjbUrHXg@mail.gmail.com>
 <744be4e0-48e0-4c77-825c-711386dd205f@arm.com> <CAJuCfpHpbz4fWawmYU=B1D5pPE4+x0Wj0V-514Dja9UWcwiL9A@mail.gmail.com>
 <a52284a4-2b8c-4118-965d-04c472fbee05@redhat.com> <CAJuCfpEbxPksw3WtLWRT9mmGUCSZ431E4vaWMtbu8OrXmMxCdw@mail.gmail.com>
 <CAJuCfpG=seLkKbMRjwuWNQozGSQmP-JqKVUuCGRqMqxND2u18A@mail.gmail.com> <3ba0015b-b36e-449a-8445-0f6272694db5@redhat.com>
In-Reply-To: <3ba0015b-b36e-449a-8445-0f6272694db5@redhat.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Wed, 6 Dec 2023 02:30:28 -0800
Message-ID: <CAJuCfpFPtbZuD53o+jOac97qA6MnK4jTEe5qNrZsH5v-m62oZA@mail.gmail.com>
Subject: Re: [PATCH v5 5/5] selftests/mm: add UFFDIO_MOVE ioctl test
To:     David Hildenbrand <david@redhat.com>
Cc:     Ryan Roberts <ryan.roberts@arm.com>, akpm@linux-foundation.org,
        viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org,
        aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com,
        hughd@google.com, mhocko@suse.com, axelrasmussen@google.com,
        rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com,
        jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com,
        kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Wed, Dec 6, 2023 at 1:21=E2=80=AFAM David Hildenbrand <david@redhat.com>=
 wrote:
>
> On 05.12.23 05:46, Suren Baghdasaryan wrote:
> > On Mon, Dec 4, 2023 at 10:44=E2=80=AFAM Suren Baghdasaryan <surenb@goog=
le.com> wrote:
> >>
> >> On Mon, Dec 4, 2023 at 10:27=E2=80=AFAM David Hildenbrand <david@redha=
t.com> wrote:
> >>>
> >>> On 04.12.23 17:35, Suren Baghdasaryan wrote:
> >>>> On Mon, Dec 4, 2023 at 1:27=E2=80=AFAM Ryan Roberts <ryan.roberts@ar=
m.com> wrote:
> >>>>>
> >>>>> On 04/12/2023 04:09, Suren Baghdasaryan wrote:
> >>>>>> On Sat, Dec 2, 2023 at 2:11=E2=80=AFAM David Hildenbrand <david@re=
dhat.com> wrote:
> >>>>>>>
> >>>>>>> On 02.12.23 09:04, Ryan Roberts wrote:
> >>>>>>>> On 01/12/2023 20:47, David Hildenbrand wrote:
> >>>>>>>>> On 01.12.23 10:29, Ryan Roberts wrote:
> >>>>>>>>>> On 21/11/2023 17:16, Suren Baghdasaryan wrote:
> >>>>>>>>>>> Add tests for new UFFDIO_MOVE ioctl which uses uffd to move s=
ource
> >>>>>>>>>>> into destination buffer while checking the contents of both a=
fter
> >>>>>>>>>>> the move. After the operation the content of the destination =
buffer
> >>>>>>>>>>> should match the original source buffer's content while the s=
ource
> >>>>>>>>>>> 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@google.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 off=
set, bool wp)
> >>>>>>>>>>>          return __copy_page(ufd, offset, false, wp);
> >>>>>>>>>>>      }
> >>>>>>>>>>>      +int move_page(int ufd, unsigned long offset, unsigned l=
ong 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 =3D (unsigned long) area_dst + offset;
> >>>>>>>>>>> +    uffdio_move.src =3D (unsigned long) area_src + offset;
> >>>>>>>>>>> +    uffdio_move.len =3D len;
> >>>>>>>>>>> +    uffdio_move.mode =3D UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
> >>>>>>>>>>> +    uffdio_move.move =3D 0;
> >>>>>>>>>>> +    if (ioctl(ufd, UFFDIO_MOVE, &uffdio_move)) {
> >>>>>>>>>>> +        /* real retval in uffdio_move.move */
> >>>>>>>>>>> +        if (uffdio_move.move !=3D -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 (err=
no=3D16,
> >>>>>>>>>> @uffd-common.c:648)
> >>>>>>>>>>
> >>>>>>>>>> I'm running in a VM on Apple M2 (arm64). I haven't debugged an=
y further, but
> >>>>>>>>>> happy to go deeper if you can direct.
> >>>>>>>>>
> >>>>>>>>> Does it trigger reliably? Which pagesize is that kernel using?
> >>>>>>>>
> >>>>>>>> Yep, although very occasionally it fails with EAGAIN. 4K kernel;=
 see other email
> >>>>>>>> for full config.
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> I can spot that uffd_move_pmd_test()/uffd_move_pmd_handle_fault=
() uses
> >>>>>>>>> default_huge_page_size(), which reads the default hugetlb size.
> >>>>>>>>
> >>>>>>>> My kernel command line is explicitly seting the default huge pag=
e size to 2M.
> >>>>>>>>
> >>>>>>>
> >>>>>>> Okay, so that likely won't affect it.
> >>>>>>>
> >>>>>>> I can only guess that it has to do with the alignment of the virt=
ual
> >>>>>>> area we are testing with, and that we do seem to get more odd pat=
terns
> >>>>>>> on arm64.
> >>>>>>>
> >>>>>>> uffd_move_test_common() is a bit more elaborate, but if we aligne=
d the
> >>>>>>> src+start area up, surely "step_count" cannot be left unmodified?
> >>>>>>>
> >>>>>>> So assuming we get either an unaligned source or an unaligned dst=
 from
> >>>>>>> mmap(), I am not convinced that we won't be moving areas that are=
 not
> >>>>>>> necessarily fully backed by PMDs and maybe don't even fall into t=
he VMA
> >>>>>>> of interest?
> >>>>>>>
> >>>>>>> Not sure if that could trigger the THP splitting issue, though.
> >>>>>>>
> >>>>>>> But I just quickly scanned that test setup, could be I am missing
> >>>>>>> something. It might make sense to just print the mmap'ed range an=
d the
> >>>>>>> actual ranges we are trying to move. Maybe something "obvious" ca=
n be
> >>>>>>> observed.
> >>>>>>
> >>>>>> I was able to reproduce the issue on an Android device and after
> >>>>>> implementing David's suggestions to split the large folio and afte=
r
> >>>>>> replacing default_huge_page_size() with read_pmd_pagesize(), the
> >>>>>> move-pmd test started working for me. Ryan, could you please apply
> >>>>>> attached patches (over mm-unstable) and try the test again?
> >>>>>
> >>>>> Yep, all fixed with those patches!
> >>>>
> >>>> Great! Thanks for testing and confirming. I'll post an updated
> >>>> patchset later today and will ask Andrew to replace the current one
> >>>> with it.
> >>>> I'll also look into the reasons we need to split PMD on ARM64 in thi=
s
> >>>> test. It's good that this happened and we were able to test the PMD
> >>>> split path but I'm curious about the reason. It's possible my addres=
s
> >>>> alignment calculations are  somehow incorrect.
> >>>
> >>> I only skimmed the diff briefly, but likely you also want to try
> >>> splitting in move_pages_pte(), if you encounter an already-pte-mapped=
 THP.
> >>
> >> Huh, good point. I might be able to move the folio splitting code into
> >> pte-mapped case and do a retry after splitting. That should minimize
> >> the additional code required. Will do and post a new set shortly.
> >> Thanks!
> >
> > Was planning to post an update today but need some more time. Will try
> > to send it tomorrow.
>
> It would be great to have tests that cover these cases (having to
> PTE-map a PMD-mapped THP, and stumbling over an already-PTE-mapped one).

Agree. Let me post the new version so that mm-unstable does not
produce these failures and will start working on covering additional
cases in the tests. The new patchset is almost ready, just finishing
final tests.

>
> --
> Cheers,
>
> David / dhildenb
>