A caller that neither owns nor may write a file may page out the COW pages of a private mapping of it, but not its file pages. When the advised range only partly covers a large file folio, the folio must be filtered out before it is split, on separate paths for PMD- and PTE-mapped folios.
Splitting a file folio unmaps all of it, and a partly covered folio can only be reclaimed after a split, so a split is the failure to look for. Check that partial MADV_PAGEOUT by such a caller leaves every mapped page of a PMD-sized shmem folio mapped, both when a PMD maps it and when a mapping of half of it maps it with PTEs. Since this checks for a split rather than for reclaim, it needs no swap. Signed-off-by: Gregory Price (Meta) <[email protected]> Reviewed-by: Sarthak Sharma <[email protected]> --- .../testing/selftests/mm/madv_cold_pageout.c | 114 ++++++++++++++++++ 1 file changed, 114 insertions(+) diff --git a/tools/testing/selftests/mm/madv_cold_pageout.c b/tools/testing/selftests/mm/madv_cold_pageout.c index f5a81d7bd08b..5a226ccbacb2 100644 --- a/tools/testing/selftests/mm/madv_cold_pageout.c +++ b/tools/testing/selftests/mm/madv_cold_pageout.c @@ -195,6 +195,33 @@ static void pte_map_thp(struct __test_metadata *_metadata, char *mapping, ASSERT_TRUE(flags & KPF_COMPOUND_HEAD); } +static char *map_aligned_file(struct __test_metadata *_metadata, int fd, + size_t size, int flags) +{ + char *mapping = reserve_aligned(_metadata, size); + + ASSERT_EQ(mmap(mapping, size, PROT_READ | PROT_WRITE, flags | MAP_FIXED, + fd, 0), mapping); + + return mapping; +} + +/* Create a PMD-sized shmem file filled with 1s. */ +static int create_shmem_file(struct __test_metadata *_metadata) +{ + char *shared; + int fd; + + fd = memfd_create("madv_cold_pageout", 0); + ASSERT_GE(fd, 0); + ASSERT_EQ(ftruncate(fd, pmd_size), 0); + shared = map_aligned_file(_metadata, fd, pmd_size, MAP_SHARED); + memset(shared, 1, pmd_size); + ASSERT_EQ(munmap(shared, pmd_size), 0); + + return fd; +} + static void assert_filled(struct __test_metadata *_metadata, const char *mapping, size_t size) { @@ -792,6 +819,93 @@ TEST_F(madv_cold_pageout, pageout_private_file_reclaims_only_cow) ASSERT_EQ(munmap(mapping, 2 * page_size), 0); } +/* + * An unauthorized caller must leave a large file folio of a private mapping + * alone, even when the advised range only partly covers it. Splitting the + * folio would unmap all of it, so every page must stay mapped, which needs + * no swap to check. See pageout_stays_within_range about other unmapping. + */ +TEST_F(madv_cold_pageout, pageout_private_file_skips_large_file_folio) +{ + char *mapping; + size_t offset; + int fd; + + if (!pmd_size) + SKIP(return, "PMD-sized THPs are not supported"); + if (geteuid()) + SKIP(return, "requires root to change credentials"); + fd = create_shmem_file(_metadata); + mapping = map_aligned_file(_metadata, fd, pmd_size, MAP_PRIVATE); + if (!collapse(mapping, pmd_size, check_huge_file)) + SKIP(return, "could not allocate a PMD-sized shmem THP"); + ASSERT_EQ(fchmod(fd, 0400), 0); + if (!drop_privileges()) + SKIP(return, "could not drop privileges"); + + ASSERT_EQ(madvise(mapping, pmd_size / 2, MADV_PAGEOUT), 0); + for (offset = 0; offset < pmd_size; offset += page_size) { + ASSERT_TRUE(page_is_present(self->pagemap_fd, + mapping + offset)) + TH_LOG("page at offset %zu was unmapped", offset); + } + assert_filled(_metadata, mapping, pmd_size); + + ASSERT_EQ(munmap(mapping, pmd_size), 0); + close(fd); +} + +/* + * The same holds for a large file folio that a private mapping maps with + * PTEs: every page the mapping maps must stay mapped. See + * pageout_stays_within_range about other unmapping. + */ +TEST_F(madv_cold_pageout, pageout_private_file_skips_pte_mapped_file_folio) +{ + const size_t size = pmd_size / 2; + char *mapping, *shared; + unsigned long pfn; + uint64_t flags; + size_t offset; + int fd; + + if (!pmd_size) + SKIP(return, "PMD-sized THPs are not supported"); + if (geteuid()) + SKIP(return, "requires root to change credentials"); + if (self->kpageflags_fd < 0) + SKIP(return, "cannot read page flags"); + fd = create_shmem_file(_metadata); + shared = map_aligned_file(_metadata, fd, pmd_size, MAP_SHARED); + if (!collapse(shared, pmd_size, check_huge_file)) + SKIP(return, "could not allocate a PMD-sized shmem THP"); + ASSERT_EQ(munmap(shared, pmd_size), 0); + + /* Mapping half of the folio leaves it mapped by PTEs. */ + mapping = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); + ASSERT_NE(mapping, MAP_FAILED); + assert_filled(_metadata, mapping, size); + pfn = pagemap_get_pfn(self->pagemap_fd, mapping); + ASSERT_NE(pfn, -1UL); + ASSERT_EQ(pageflags_get(pfn, self->kpageflags_fd, &flags), 0); + if (!(flags & KPF_COMPOUND_HEAD)) + SKIP(return, "the shmem THP was split"); + ASSERT_EQ(fchmod(fd, 0400), 0); + if (!drop_privileges()) + SKIP(return, "could not drop privileges"); + + ASSERT_EQ(madvise(mapping, size / 2, MADV_PAGEOUT), 0); + for (offset = 0; offset < size; offset += page_size) { + ASSERT_TRUE(page_is_present(self->pagemap_fd, + mapping + offset)) + TH_LOG("page at offset %zu was unmapped", offset); + } + assert_filled(_metadata, mapping, size); + + ASSERT_EQ(munmap(mapping, size), 0); + close(fd); +} + /* Swap out an anonymous page, to see whether swap works at all. */ static bool probe_swap(int pagemap_fd) { -- 2.56.0
