When checking for actual tail or head pages of a folio, we must make sure that the KPF_COMPOUND_HEAD/KPF_COMPOUND_TAIL flag is paired with KPF_THP.
For example, if we have another large folio after our large folio in physical memory, our "pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL" would trigger even though it's actually a head page of the next folio.
If is_backed_by_folio() returns a wrong result, split_pte_mapped_thp() can fail with "Some THPs are missing during mremap".
Fix it by checking for head/tail pages of folios properly. Add folio_tail_flags/folio_head_flags to improve readability and use these masks also when just testing for any compound page.
Fixes: 169b456b0162 ("selftests/mm: reimplement is_backed_by_thp() with more precise check") Signed-off-by: David Hildenbrand david@redhat.com --- tools/testing/selftests/mm/split_huge_page_test.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c index 10ae65ea032f6..72d6d8bb329ed 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -44,6 +44,8 @@ int kpageflags_fd; static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd) { + const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD; + const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL; const unsigned long nr_pages = 1UL << order; unsigned long pfn_head; uint64_t pfn_flags; @@ -61,7 +63,7 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
/* check for order-0 pages */ if (!order) { - if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL)) + if (pfn_flags & (folio_head_flags | folio_tail_flags)) return false; return true; } @@ -76,14 +78,14 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, goto fail;
/* head PFN has no compound_head flag set */ - if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD))) + if ((pfn_flags & folio_head_flags) != folio_head_flags) return false;
/* check all tail PFN flags */ for (i = 1; i < nr_pages; i++) { if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags)) goto fail; - if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL))) + if ((pfn_flags & folio_tail_flags) != folio_tail_flags) return false; }
@@ -94,11 +96,8 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags)) return true;
- /* this folio is bigger than the given order */ - if (pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)) - return false; - - return true; + /* If we find another tail page, then the folio is larger. */ + return (pfn_flags & folio_tail_flags) != folio_tail_flags; fail: ksft_exit_fail_msg("Failed to get folio info\n"); return false;