tools/testing/selftests/mm: add smaps visibility guard region test

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.

Link: https://lkml.kernel.org/r/059e62b8c67e55e6d849878206a95ea1d7c1e885.1763460113.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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);
@@ -2203,4 +2252,75 @@ TEST_F(guard_regions, collapse)
 	}
 }
 
+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

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;

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);