On Wed, Oct 29, 2025 at 9:51 AM Lorenzo Stoakes lorenzo.stoakes@oracle.com wrote:
Assert that we observe guard regions appearing in /proc/$pid/smaps as expected, and when split/merge is performed too (with expected sticky behaviour).
Also add handling for file systems which don't sanely handle mmap() VMA merging so we don't incorrectly encounter a test failure in this situation.
Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
Reviewed-by: Suren Baghdasaryan surenb@google.com
tools/testing/selftests/mm/guard-regions.c | 120 +++++++++++++++++++++ tools/testing/selftests/mm/vm_util.c | 5 + tools/testing/selftests/mm/vm_util.h | 1 + 3 files changed, 126 insertions(+)
diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c index 8dd81c0a4a5a..a9be11e03a6a 100644 --- a/tools/testing/selftests/mm/guard-regions.c +++ b/tools/testing/selftests/mm/guard-regions.c @@ -94,6 +94,7 @@ static void *mmap_(FIXTURE_DATA(guard_regions) * self, case ANON_BACKED: flags |= MAP_PRIVATE | MAP_ANON; fd = -1;
offset = 0; break; case SHMEM_BACKED: case LOCAL_FILE_BACKED:@@ -260,6 +261,54 @@ static bool is_buf_eq(char *buf, size_t size, char chr) return true; }
+/*
- Some file systems have issues with merging due to changing merge-sensitive
- parameters in the .mmap callback, and prior to .mmap_prepare being
- implemented everywhere this will now result in an unexpected failure to
- merge (e.g. - overlayfs).
- Perform a simple test to see if the local file system suffers from this, if
- it does then we can skip test logic that assumes local file system merging is
- sane.
- */
+static bool local_fs_has_sane_mmap(FIXTURE_DATA(guard_regions) * self,
const FIXTURE_VARIANT(guard_regions) * variant)+{
const unsigned long page_size = self->page_size;char *ptr, *ptr2;struct procmap_fd procmap;if (variant->backing != LOCAL_FILE_BACKED)return true;/* Map 10 pages. */ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0);if (ptr == MAP_FAILED)return false;/* Unmap the middle. */munmap(&ptr[5 * page_size], page_size);/* Map again. */ptr2 = mmap_(self, variant, &ptr[5 * page_size], page_size, PROT_READ | PROT_WRITE,MAP_FIXED, 5 * page_size);if (ptr2 == MAP_FAILED)return false;/* Now make sure they all merged. */if (open_self_procmap(&procmap) != 0)return false;if (!find_vma_procmap(&procmap, ptr))return false;if (procmap.query.vma_start != (unsigned long)ptr)return false;if (procmap.query.vma_end != (unsigned long)ptr + 10 * page_size)return false;close_procmap(&procmap);return true;+}
FIXTURE_SETUP(guard_regions) { self->page_size = (unsigned long)sysconf(_SC_PAGESIZE); @@ -2138,4 +2187,75 @@ TEST_F(guard_regions, pagemap_scan) ASSERT_EQ(munmap(ptr, 10 * page_size), 0); }
+TEST_F(guard_regions, smaps) +{
const unsigned long page_size = self->page_size;struct procmap_fd procmap;char *ptr, *ptr2;int i;/* Map a region. */ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0);ASSERT_NE(ptr, MAP_FAILED);/* We shouldn't yet see a guard flag. */ASSERT_FALSE(check_vmflag_guard(ptr));/* Install a single guard region. */ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);/* Now we should see a guard flag. */ASSERT_TRUE(check_vmflag_guard(ptr));/** Removing the guard region should not change things because we simply* cannot accurately track whether a given VMA has had all of its guard* regions removed.*/ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_REMOVE), 0);ASSERT_TRUE(check_vmflag_guard(ptr));/* Install guard regions throughout. */for (i = 0; i < 10; i++) {ASSERT_EQ(madvise(&ptr[i * page_size], page_size, MADV_GUARD_INSTALL), 0);/* We should always see the guard region flag. */ASSERT_TRUE(check_vmflag_guard(ptr));}/* Split into two VMAs. */ASSERT_EQ(munmap(&ptr[4 * page_size], page_size), 0);/* Both VMAs should have the guard flag set. */ASSERT_TRUE(check_vmflag_guard(ptr));ASSERT_TRUE(check_vmflag_guard(&ptr[5 * page_size]));/** If the local file system is unable to merge VMAs due to having* unusual characteristics, there is no point in asserting merge* behaviour.*/if (!local_fs_has_sane_mmap(self, variant)) {TH_LOG("local filesystem does not support sane merging skipping merge test");return;}/* Map a fresh VMA between the two split VMAs. */ptr2 = mmap_(self, variant, &ptr[4 * page_size], page_size,PROT_READ | PROT_WRITE, MAP_FIXED, 4 * page_size);ASSERT_NE(ptr2, MAP_FAILED);/** Check the procmap to ensure that this VMA merged with the adjacent* two. The guard region flag is 'sticky' so should not preclude* merging.*/ASSERT_EQ(open_self_procmap(&procmap), 0);ASSERT_TRUE(find_vma_procmap(&procmap, ptr));ASSERT_EQ(procmap.query.vma_start, (unsigned long)ptr);ASSERT_EQ(procmap.query.vma_end, (unsigned long)ptr + 10 * page_size);ASSERT_EQ(close_procmap(&procmap), 0);/* And, of course, this VMA should have the guard flag set. */ASSERT_TRUE(check_vmflag_guard(ptr));+}
TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c index e33cda301dad..605cb58ea5c3 100644 --- a/tools/testing/selftests/mm/vm_util.c +++ b/tools/testing/selftests/mm/vm_util.c @@ -449,6 +449,11 @@ bool check_vmflag_pfnmap(void *addr) return check_vmflag(addr, "pf"); }
+bool check_vmflag_guard(void *addr) +{
return check_vmflag(addr, "gu");+}
bool softdirty_supported(void) { char *addr; diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h index 26c30fdc0241..a8abdf414d46 100644 --- a/tools/testing/selftests/mm/vm_util.h +++ b/tools/testing/selftests/mm/vm_util.h @@ -98,6 +98,7 @@ int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len, unsigned long get_free_hugepages(void); bool check_vmflag_io(void *addr); bool check_vmflag_pfnmap(void *addr); +bool check_vmflag_guard(void *addr); int open_procmap(pid_t pid, struct procmap_fd *procmap_out); int query_procmap(struct procmap_fd *procmap); bool find_vma_procmap(struct procmap_fd *procmap, void *address); -- 2.51.0