On 1 Sep 2025, at 3:22, David Hildenbrand wrote:
On 31.08.25 04:27, Wei Yang wrote:
Subject: "selftests/mm: verify page content after remapping PMD through PTEs"
After mremap(), add a check on content to see whether mremap corrupt data.
Signed-off-by: Wei Yang richard.weiyang@gmail.com
v2: add check on content instead of just test backed folio
I'm confused, don't we have that exact check later in the function?
Your v1 might have been better, unless I am missing something.
tools/testing/selftests/mm/split_huge_page_test.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c index 10ae65ea032f..229b6dcabece 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -423,10 +423,14 @@ static void split_pte_mapped_thp(void) /* smap does not show THPs after mremap, use kpageflags instead */ thp_size = 0;
- for (i = 0; i < pagesize * 4; i++)
- for (i = 0; i < pagesize * 4; i++) {
if (pte_mapped[i] != (char)i)ksft_exit_fail_msg("%ld byte corrupted\n", i);- if (i % pagesize == 0 && is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd)) thp_size++;
- } if (thp_size != 4) ksft_exit_fail_msg("Some THPs are missing during mremap\n");
I'm a bit confused with this test in general.
We do a
pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);
which I read as a "NOP".
Questions
(a) Will this actually do anything? Also, maybe it does now, but can't the kernel just optimize that out in the future?
It remaps each subpage of 4 PMD THPs into a contiguous 2MB vaddr range and perform split on that range.
(b) Is it even guaranteed that we can access > pagesize afterwards? I mean, we specify MREMAP_MAYMOVE.
I would suggest to just use mprotect/madvise to pte-map a PMD-THP.
If you want to test that, please add your own test case.
-- Best Regards, Yan, Zi