Re: [PATCH v5 5/5] selftests/mm: add UFFDIO_MOVE ioctl test

From: David Hildenbrand <david@redhat.com>
To: Ryan Roberts <ryan.roberts@arm.com>,
	Suren Baghdasaryan <surenb@google.com>,
	akpm@linux-foundation.org
Cc: 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
Subject: Re: [PATCH v5 5/5] selftests/mm: add UFFDIO_MOVE ioctl test
Date: Fri, 1 Dec 2023 21:47:07 +0100	[thread overview]
Message-ID: <a41c759f-78d8-44ed-b708-1bb737a8e6c1@redhat.com> (raw)
In-Reply-To: <b3c882d2-0135-430c-8179-784f78be0902@arm.com>

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@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 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?

I can spot that uffd_move_pmd_test()/uffd_move_pmd_handle_fault() uses 
default_huge_page_size(), which reads the default hugetlb size.

That, however, does not necessarily correspond to the THP size. That one 
can be obtained using read_pmd_pagesize() in vm_util.c

I quickly scanned the code (still want to take a deeper look), but all 
PAE checks looked sane to me.

I think the issue is folio split handling. I replied to the patch.

-- 
Cheers,

David / dhildenb