linux-kernel - [PATCH 2/2] userfaultfd: selftests: modify selftest to use /dev/userfaultfd

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Message-Id: <20220412202942.386981-2-axelrasmussen@google.com>
Date:   Tue, 12 Apr 2022 13:29:42 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>,
        Shuah Khan <shuah@...nel.org>
Cc:     Axel Rasmussen <axelrasmussen@...gle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: [PATCH 2/2] userfaultfd: selftests: modify selftest to use /dev/userfaultfd

Prefer this new interface, but if using it fails for any reason just
fall back to using userfaultfd(2) as before.

Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 92a4516f8f0d..a50c430f036c 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -383,13 +383,32 @@ static void assert_expected_ioctls_present(uint64_t mode, uint64_t ioctls)
 	}
 }
 
+static void __userfaultfd_open_dev(void)
+{
+	int fd;
+
+	uffd = -1;
+	fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
+	if (fd < 0)
+		return;
+
+	uffd = ioctl(fd, USERFAULTFD_IOC_NEW,
+		     O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
+	close(fd);
+}
+
 static void userfaultfd_open(uint64_t *features)
 {
 	struct uffdio_api uffdio_api;
 
-	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
+	__userfaultfd_open_dev();
+	if (uffd < 0) {
+		printf("/dev/userfaultfd failed, fallback to userfaultfd(2)\n");
+		uffd = syscall(__NR_userfaultfd,
+			       O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
+	}
 	if (uffd < 0)
-		err("userfaultfd syscall not available in this kernel");
+		err("userfaultfd syscall failed");
 	uffd_flags = fcntl(uffd, F_GETFD, NULL);
 
 	uffdio_api.api = UFFD_API;
-- 
2.35.1.1178.g4f1659d476-goog