userfaultfd: Add test using /dev/userfaultfd instead of syscall

Signed-off-by: Ricardo Branco <[email protected]>

Author: ricardobranco777

runtest/syscalls

@@ -1772,6 +1772,7 @@ umount2_02 umount2_02
 userfaultfd01 userfaultfd01
 userfaultfd02 userfaultfd02
 userfaultfd03 userfaultfd03
+userfaultfd04 userfaultfd04
 
 ustat01 ustat01
 ustat02 ustat02

testcases/kernel/syscalls/userfaultfd/.gitignore

@@ -1,3 +1,4 @@
 /userfaultfd01
 /userfaultfd02
 /userfaultfd03
+/userfaultfd04

testcases/kernel/syscalls/userfaultfd/Makefile

@@ -14,3 +14,4 @@ include $(top_srcdir)/include/mk/generic_leaf_target.mk
 userfaultfd01: CFLAGS += -pthread
 userfaultfd02: CFLAGS += -pthread
 userfaultfd03: CFLAGS += -pthread
+userfaultfd04: CFLAGS += -pthread

testcases/kernel/syscalls/userfaultfd/userfaultfd04.c

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025 SUSE LLC
+ * Author: Christian Amann <[email protected]>
+ * Author: Ricardo Branco <[email protected]>
+ */
+
+/*\
+ * Force a pagefault event and handle it using :man2:`userfaultfd`
+ * from a different thread using /dev/userfaultfd instead of syscall.
+ */
+
+#include "config.h"
+#include <poll.h>
+#include "tst_test.h"
+#include "tst_safe_macros.h"
+#include "tst_safe_pthread.h"
+#include "lapi/userfaultfd.h"
+
+static int page_size;
+static char *page;
+static void *copy_page;
+static int uffd;
+
+static int open_userfaultfd(int flags)
+{
+	int fd, fd2;
+
+	fd = SAFE_OPEN("/dev/userfaultfd", O_RDWR);
+
+	fd2 = SAFE_IOCTL(fd, USERFAULTFD_IOC_NEW, flags);
+
+	SAFE_CLOSE(fd);
+
+	return fd2;
+}
+
+static void set_pages(void)
+{
+	page_size = sysconf(_SC_PAGE_SIZE);
+	page = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	copy_page = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+}
+
+static void handle_thread(void)
+{
+	static struct uffd_msg msg;
+	struct uffdio_copy uffdio_copy;
+
+	struct pollfd pollfd;
+	int nready;
+
+	pollfd.fd = uffd;
+	pollfd.events = POLLIN;
+	nready = poll(&pollfd, 1, -1);
+	if (nready == -1)
+		tst_brk(TBROK | TERRNO, "Error on poll");
+
+	SAFE_READ(1, uffd, &msg, sizeof(msg));
+
+	if (msg.event != UFFD_EVENT_PAGEFAULT)
+		tst_brk(TBROK | TERRNO, "Received unexpected UFFD_EVENT");
+
+	memset(copy_page, 'X', page_size);
+
+	uffdio_copy.src = (unsigned long) copy_page;
+
+	uffdio_copy.dst = (unsigned long) msg.arg.pagefault.address
+			& ~(page_size - 1);
+	uffdio_copy.len = page_size;
+	uffdio_copy.mode = 0;
+	uffdio_copy.copy = 0;
+	SAFE_IOCTL(uffd, UFFDIO_COPY, &uffdio_copy);
+
+	close(uffd);
+}
+
+static void run(void)
+{
+	pthread_t thr;
+	struct uffdio_api uffdio_api;
+	struct uffdio_register uffdio_register;
+
+	set_pages();
+
+	TEST(open_userfaultfd(O_CLOEXEC | O_NONBLOCK));
+
+	if (TST_RET == -1) {
+		if (TST_ERR == EPERM) {
+			tst_brk(TCONF, "Hint: check /dev/userfaultfd permissions");
+		} else
+			tst_brk(TBROK | TTERRNO,
+				"Could not create userfault file descriptor");
+	}
+
+	uffd = TST_RET;
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = 0;
+	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
+
+	uffdio_register.range.start = (unsigned long) page;
+	uffdio_register.range.len = page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+
+	SAFE_IOCTL(uffd, UFFDIO_REGISTER, &uffdio_register);
+
+	SAFE_PTHREAD_CREATE(&thr, NULL,
+			(void * (*)(void *)) handle_thread, NULL);
+
+	char c = page[0xf];
+
+	if (c == 'X')
+		tst_res(TPASS, "Pagefault handled via /dev/userfaultfd");
+	else
+		tst_res(TFAIL, "Pagefault not handled via /dev/userfaultfd");
+
+	SAFE_PTHREAD_JOIN(thr, NULL);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.min_kver = "5.11",
+};