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Message-ID: <d5a0f735783fb4f30a604f570ede02ccc5e29be9.1763399675.git.lorenzo.stoakes@oracle.com>
Date: Mon, 17 Nov 2025 17:33:39 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...nel.org>,
"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>,
Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] testing/selftests/mm: add soft-dirty merge self-test
Assert that we correctly merge VMAs containing VM_SOFTDIRTY flags now that
we correctly handle these as sticky.
In order to do so, we have to account for the fact the pagemap interface
checks soft dirty PTEs and additionally that newly merged VMAs are marked
VM_SOFTDIRTY.
We do this by using use unfaulted anon VMAs, establishing one and clearing
references on that one, before establishing another and merging the two
before checking that soft-dirty is propagated as expected.
We check that this functions correctly with mremap() and mprotect() as
sample cases, because VMA merge of adjacent newly mapped VMAs will
automatically be made soft-dirty due to existing logic which does so.
We are therefore exercising other means of merging VMAs.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
tools/testing/selftests/mm/soft-dirty.c | 127 +++++++++++++++++++++++-
1 file changed, 126 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/mm/soft-dirty.c b/tools/testing/selftests/mm/soft-dirty.c
index 4ee4db3750c1..4c73820070ba 100644
--- a/tools/testing/selftests/mm/soft-dirty.c
+++ b/tools/testing/selftests/mm/soft-dirty.c
@@ -184,6 +184,130 @@ static void test_mprotect(int pagemap_fd, int pagesize, bool anon)
close(test_fd);
}
+static void test_merge(int pagemap_fd, int pagesize)
+{
+ char *reserved, *map, *map2;
+
+ /*
+ * Reserve space for tests:
+ *
+ * ---padding to ---
+ * | avoid adj. |
+ * v merge v
+ * |---|---|---|---|---|
+ * | | 1 | 2 | 3 | |
+ * |---|---|---|---|---|
+ */
+ reserved = mmap(NULL, 5 * pagesize, PROT_NONE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ if (reserved == MAP_FAILED)
+ ksft_exit_fail_msg("mmap failed\n");
+ munmap(reserved, 4 * pagesize);
+
+ /*
+ * Establish initial VMA:
+ *
+ * S/D
+ * |---|---|---|---|---|
+ * | | 1 | | | |
+ * |---|---|---|---|---|
+ */
+ map = mmap(&reserved[pagesize], pagesize, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+ if (map == MAP_FAILED)
+ ksft_exit_fail_msg("mmap failed\n");
+
+ /* This will clear VM_SOFTDIRTY too. */
+ clear_softdirty();
+
+ /*
+ * Now place a new mapping which will be marked VM_SOFTDIRTY. Away from
+ * map:
+ *
+ * - S/D
+ * |---|---|---|---|---|
+ * | | 1 | | 2 | |
+ * |---|---|---|---|---|
+ */
+ map2 = mmap(&reserved[3 * pagesize], pagesize, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+ if (map2 == MAP_FAILED)
+ ksft_exit_fail_msg("mmap failed\n");
+
+ /*
+ * Now remap it immediately adjacent to map, if the merge correctly
+ * propagates VM_SOFTDIRTY, we should then observe the VMA as a whole
+ * being marked soft-dirty:
+ *
+ * merge
+ * S/D
+ * |---|-------|---|---|
+ * | | 1 | | |
+ * |---|-------|---|---|
+ */
+ map2 = mremap(map2, pagesize, pagesize, MREMAP_FIXED | MREMAP_MAYMOVE,
+ &reserved[2 * pagesize]);
+ if (map2 == MAP_FAILED)
+ ksft_exit_fail_msg("mremap failed\n");
+ ksft_test_result(pagemap_is_softdirty(pagemap_fd, map) == 1,
+ "Test %s-anon soft-dirty after remap merge 1st pg\n",
+ __func__);
+ ksft_test_result(pagemap_is_softdirty(pagemap_fd, map2) == 1,
+ "Test %s-anon soft-dirty after remap merge 2nd pg\n",
+ __func__);
+
+ munmap(map, 2 * pagesize);
+
+ /*
+ * Now establish another VMA:
+ *
+ * S/D
+ * |---|---|---|---|---|
+ * | | 1 | | | |
+ * |---|---|---|---|---|
+ */
+ map = mmap(&reserved[pagesize], pagesize, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+ if (map == MAP_FAILED)
+ ksft_exit_fail_msg("mmap failed\n");
+
+ /* Clear VM_SOFTDIRTY... */
+ clear_softdirty();
+ /* ...and establish incompatible adjacent VMA:
+ *
+ * - S/D
+ * |---|---|---|---|---|
+ * | | 1 | 2 | | |
+ * |---|---|---|---|---|
+ */
+ map2 = mmap(&reserved[2 * pagesize], pagesize,
+ PROT_READ | PROT_WRITE | PROT_EXEC,
+ MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
+ if (map2 == MAP_FAILED)
+ ksft_exit_fail_msg("mmap failed\n");
+
+ /*
+ * Now mprotect() VMA 1 so it's compatible with 2 and therefore merges:
+ *
+ * merge
+ * S/D
+ * |---|-------|---|---|
+ * | | 1 | | |
+ * |---|-------|---|---|
+ */
+ if (mprotect(map, pagesize, PROT_READ | PROT_WRITE | PROT_EXEC))
+ ksft_exit_fail_msg("mprotect failed\n");
+
+ ksft_test_result(pagemap_is_softdirty(pagemap_fd, map) == 1,
+ "Test %s-anon soft-dirty after mprotect merge 1st pg\n",
+ __func__);
+ ksft_test_result(pagemap_is_softdirty(pagemap_fd, map2) == 1,
+ "Test %s-anon soft-dirty after mprotect merge 2nd pg\n",
+ __func__);
+
+ munmap(map, 2 * pagesize);
+}
+
static void test_mprotect_anon(int pagemap_fd, int pagesize)
{
test_mprotect(pagemap_fd, pagesize, true);
@@ -204,7 +328,7 @@ int main(int argc, char **argv)
if (!softdirty_supported())
ksft_exit_skip("soft-dirty is not support\n");
- ksft_set_plan(15);
+ ksft_set_plan(19);
pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
if (pagemap_fd < 0)
ksft_exit_fail_msg("Failed to open %s\n", PAGEMAP_FILE_PATH);
@@ -216,6 +340,7 @@ int main(int argc, char **argv)
test_hugepage(pagemap_fd, pagesize);
test_mprotect_anon(pagemap_fd, pagesize);
test_mprotect_file(pagemap_fd, pagesize);
+ test_merge(pagemap_fd, pagesize);
close(pagemap_fd);
--
2.51.0
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