[LTP] [PATCH v2] userfaultfd: Use two-step handshake to probe features

[Ricardo Branco]

userfaultfd05 and userfaultfd06 assume that
UFFD_FEATURE_PAGEFAULT_FLAG_WP and UFFD_FEATURE_POISON are available
when setting up userfaultfd.

On kernels where either feature is unavailable at runtime,
UFFDIO_API fails with EINVAL and the tests end up as TBROK instead of
being skipped.

Fix this by using the required two-step handshake and skip with TCONF
if the required feature bit is absent.

Fixes: 1840ee23d172b5ab04cca7c2acfa48755b041911
Link: https://github.com/linux-test-project/ltp/issues/1289

Signed-off-by: Ricardo Branco <rbranco@suse.de>
---
 .../kernel/syscalls/userfaultfd/userfaultfd05.c   | 12 +++++++++++-
 .../kernel/syscalls/userfaultfd/userfaultfd06.c   | 15 +++++++++++----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
index e25a227cf..e6386ce76 100644
--- a/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
@@ -82,10 +82,20 @@ static void *handle_thread(void)
 static void run(void)
 {
 	pthread_t thr;
-	struct uffdio_api uffdio_api;
+	struct uffdio_api uffdio_api = {};
 	struct uffdio_register uffdio_register;
 	struct uffdio_writeprotect uffdio_writeprotect;
 
+	/*
+	 * Two-step handshake to check if feature is available
+	 */
+	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
+	uffdio_api.api = UFFD_API;
+	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
+	if (!(uffdio_api.features & UFFD_FEATURE_PAGEFAULT_FLAG_WP))
+		tst_brk(TCONF, "UFFD_FEATURE_PAGEFAULT_FLAG_WP not supported");
+	SAFE_CLOSE(uffd);
+
 	set_pages();
 
 	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
index 5b1252c35..e1b3c2f6f 100644
--- a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
@@ -97,18 +97,25 @@ static void run(void)
 
 	poison_fault_seen = 0;
 	sigbus_seen = 0;
-	set_pages();
 
+	/*
+	 * Two-step handshake to check if feature is available
+	 */
 	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
+	uffdio_api.api = UFFD_API;
+	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
+	if (!(uffdio_api.features & UFFD_FEATURE_POISON))
+		tst_brk(TCONF, "UFFD_FEATURE_POISON not supported");
+	SAFE_CLOSE(uffd);
 
+	set_pages();
+
+	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
 	uffdio_api.api = UFFD_API;
 	uffdio_api.features = UFFD_FEATURE_POISON;
 
 	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
 
-	if (!(uffdio_api.features & UFFD_FEATURE_POISON))
-		tst_brk(TCONF, "UFFD_FEATURE_POISON not supported");
-
 	uffdio_register.range.start = (unsigned long) page;
 	uffdio_register.range.len = page_size;
 	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
-- 
2.53.0