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[2003:cb:c722:3700:6501:8925:6f9:fcdc]) by smtp.gmail.com with ESMTPSA id w3-20020a5d6803000000b003333eadd206sm6363571wru.27.2023.12.04.10.27.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Dec 2023 10:27:34 -0800 (PST) Message-ID: Date: Mon, 4 Dec 2023 19:27:32 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 5/5] selftests/mm: add UFFDIO_MOVE ioctl test Content-Language: en-US To: Suren Baghdasaryan , Ryan Roberts Cc: 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 References: <20231121171643.3719880-1-surenb@google.com> <20231121171643.3719880-6-surenb@google.com> <744be4e0-48e0-4c77-825c-711386dd205f@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 04.12.23 17:35, Suren Baghdasaryan wrote: > On Mon, Dec 4, 2023 at 1:27 AM Ryan Roberts wrote: >> >> On 04/12/2023 04:09, Suren Baghdasaryan wrote: >>> On Sat, Dec 2, 2023 at 2:11 AM David Hildenbrand 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 >>>>>>>> --- >>>>>>>> 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! > > 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 this > 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 address > 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. -- Cheers, David / dhildenb