[LTP] [PATCH v4 2/3] 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>
---
 testcases/kernel/syscalls/userfaultfd/userfaultfd05.c | 8 +++++++-
 testcases/kernel/syscalls/userfaultfd/userfaultfd06.c | 6 +++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
index 59956d85d..a42ac09bd 100644
--- a/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd05.c
@@ -22,6 +22,11 @@ static char *page;
 static int uffd = -1;
 static volatile int wp_fault_seen;
 
+static void setup(void)
+{
+	CHECK_UFFD_FEATURE(UFFD_FEATURE_PAGEFAULT_FLAG_WP);
+}
+
 static void set_pages(void)
 {
 	page_size = SAFE_SYSCONF(_SC_PAGE_SIZE);
@@ -87,7 +92,7 @@ static void *handle_thread(void *arg LTP_ATTRIBUTE_UNUSED)
 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;
 
@@ -127,6 +132,7 @@ static void run(void)
 }
 
 static struct tst_test test = {
+	.setup = setup,
 	.test_all = run,
 	.min_kver = "5.7",
 	.needs_kconfigs = (const char *[]) {
diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
index ec93d8ad6..1ab288e64 100644
--- a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
@@ -38,6 +38,8 @@ static void setup(void)
 {
 	struct sigaction sa = {};
 
+	CHECK_UFFD_FEATURE(UFFD_FEATURE_POISON);
+
 	sa.sa_handler = sigbus_handler;
 	sigemptyset(&sa.sa_mask);
 	SAFE_SIGACTION(SIGBUS, &sa, NULL);
@@ -99,6 +101,7 @@ static void run(void)
 
 	poison_fault_seen = 0;
 	sigbus_seen = 0;
+
 	set_pages();
 
 	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
@@ -108,9 +111,6 @@ static void run(void)
 
 	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;
-- 
2.54.0