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Message-ID: <b535069ea375281fcbeb7c60b615bca0bb92982c.1762422915.git.lorenzo.stoakes@oracle.com>
Date: Thu, 6 Nov 2025 10:46:16 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Jonathan Corbet <corbet@....net>, David Hildenbrand <david@...hat.com>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-mm@...ck.org,
linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
Andrei Vagin <avagin@...il.com>
Subject: [PATCH v2 5/5] selftests/mm/guard-regions: add smaps visibility 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.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.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
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