On 04/12/2023 04:09, Suren Baghdasaryan wrote:
> On Sat, Dec 2, 2023 at 2:11 AM David Hildenbrand <david@xxxxxxxxxx> 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 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@xxxxxxxxxx>
>>>>>> ---
>>>>>> 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.
>>>>
>>>> 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 page 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 virtual
>> area we are testing with, and that we do seem to get more odd patterns
>> on arm64.
>>
>> uffd_move_test_common() is a bit more elaborate, but if we aligned 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 the 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 and the
>> actual ranges we are trying to move. Maybe something "obvious" can 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 after
> 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!
> Thanks,
> Suren.
>
>>
>> --
>> Cheers,
>>
>> David / dhildenb
>>
