The current implementation of test_unmerge_uffd_wp() explicitly sets
`uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP` before calling
UFFDIO_API. This can cause the ioctl() call to fail with EINVAL on kernels
that do not support UFFD-WP, leading the test to fail unnecessarily:
# ------------------------------
# running ./ksm_functional_tests
# ------------------------------
# TAP version 13
# 1..9
# # [RUN] test_unmerge
# ok 1 Pages were unmerged
# # [RUN] test_unmerge_zero_pages
# ok 2 KSM zero pages were unmerged
# # [RUN] test_unmerge_discarded
# ok 3 Pages were unmerged
# # [RUN] test_unmerge_uffd_wp
# not ok 4 UFFDIO_API failed <-----
# # [RUN] test_prot_none
# ok 5 Pages were unmerged
# # [RUN] test_prctl
# ok 6 Setting/clearing PR_SET_MEMORY_MERGE works
# # [RUN] test_prctl_fork
# # No pages got merged
# # [RUN] test_prctl_fork_exec
# ok 7 PR_SET_MEMORY_MERGE value is inherited
# # [RUN] test_prctl_unmerge
# ok 8 Pages were unmerged
# Bail out! 1 out of 8 tests failed
# # Planned tests != run tests (9 != 8)
# # Totals: pass:7 fail:1 xfail:0 xpass:0 skip:0 error:0
# [FAIL]
This patch improves compatibility and robustness of the UFFD-WP test
(test_unmerge_uffd_wp) by correctly implementing the UFFDIO_API
two-step handshake as recommended by the userfaultfd(2) man page.
Key changes:
1. Use features=0 in the initial UFFDIO_API call to query supported
feature bits, rather than immediately requesting WP support.
2. Skip the test gracefully if:
- UFFDIO_API fails with EINVAL (e.g. unsupported API version), or
- UFFD_FEATURE_PAGEFAULT_FLAG_WP is not advertised by the kernel.
3. Close the initial userfaultfd and create a new one before enabling
the required feature, since UFFDIO_API can only be called once per fd.
4. Improve diagnostics by distinguishing between expected and unexpected
failures, using strerror() to report errors.
This ensures the test behaves correctly across a wider range of kernel
versions and configurations, while preserving the intended behavior on
kernels that support UFFD-WP.
Suggestted-by: David Hildenbrand <da...@redhat.com>
Signed-off-by: Li Wang <liw...@redhat.com>
Cc: Peter Xu <pet...@redhat.com>
Cc: Nadav Amit <nadav.a...@gmail.com>
Cc: Aruna Ramakrishna <aruna.ramakris...@oracle.com>
Cc: Bagas Sanjaya <bagasdo...@gmail.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Joey Gouly <joey.go...@arm.com>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Keith Lucas <keith.lu...@oracle.com>
Cc: Ryan Roberts <ryan.robe...@arm.com>
Cc: Shuah Khan <sh...@kernel.org>
Acked-by: David Hildenbrand <da...@redhat.com>
---
.../selftests/mm/ksm_functional_tests.c | 28 +++++++++++++++++--
1 file changed, 26 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c
b/tools/testing/selftests/mm/ksm_functional_tests.c
index b61803e36d1c..d8bd1911dfc0 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -393,9 +393,13 @@ static void test_unmerge_uffd_wp(void)
/* See if UFFD-WP is around. */
uffdio_api.api = UFFD_API;
- uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+ uffdio_api.features = 0;
if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) {
- ksft_test_result_fail("UFFDIO_API failed\n");
+ if (errno == EINVAL)
+ ksft_test_result_skip("The API version requested is not
supported\n");
+ else
+ ksft_test_result_fail("UFFDIO_API failed: %s\n",
strerror(errno));
+
goto close_uffd;
}
if (!(uffdio_api.features & UFFD_FEATURE_PAGEFAULT_FLAG_WP)) {
@@ -403,6 +407,26 @@ static void test_unmerge_uffd_wp(void)
goto close_uffd;
}
+ /*
+ * UFFDIO_API must only be called once to enable features.
+ * So we close the old userfaultfd and create a new one to
+ * actually enable UFFD_FEATURE_PAGEFAULT_FLAG_WP.
+ */
+ close(uffd);
+ uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+ if (uffd < 0) {
+ ksft_test_result_fail("__NR_userfaultfd failed\n");
+ goto unmap;
+ }
+
+ /* Now, enable it ("two-step handshake") */
+ uffdio_api.api = UFFD_API;
+ uffdio_api.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+ if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) {
+ ksft_test_result_fail("UFFDIO_API failed: %s\n",
strerror(errno));
+ goto close_uffd;
+ }
+
/* Register UFFD-WP, no need for an actual handler. */
if (uffd_register(uffd, map, size, false, true, false)) {
ksft_test_result_fail("UFFDIO_REGISTER_MODE_WP failed\n");
--
2.49.0
