userfaultfd: Add test using UFFDIO_ZEROPAGE

Signed-off-by: Ricardo Branco <rbranco@suse.de>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Link: #1280

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 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025 SUSE LLC
+ * Author: Christian Amann <camann@suse.com>
+ * Author: Ricardo Branco <rbranco@suse.com>
+ */
+
+/*\
+ * Force a pagefault event and handle it using :manpage:`userfaultfd(2)`
+ * from a different thread using UFFDIO_ZEROPAGE.
+ */
+
+#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 int uffd;
+
+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);
+}
+
+static void reset_pages(void)
+{
+	SAFE_MUNMAP(page, page_size);
+}
+
+static void *handle_thread(void)
+{
+	static struct uffd_msg msg;
+	struct uffdio_zeropage uffdio_zeropage = {};
+
+	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 %d", msg.event);
+
+	uffdio_zeropage.range.start	= msg.arg.pagefault.address
+					& ~(page_size - 1);
+	uffdio_zeropage.range.len	= page_size;
+
+	SAFE_IOCTL(uffd, UFFDIO_ZEROPAGE, &uffdio_zeropage);
+
+	close(uffd);
+	return NULL;
+}
+
+static void run(void)
+{
+	pthread_t thr;
+	struct uffdio_api uffdio_api = {};
+	struct uffdio_register uffdio_register;
+
+	set_pages();
+
+	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
+
+	uffdio_api.api = UFFD_API;
+	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 *) handle_thread, NULL);
+
+	for (int i = 0; i < page_size; i++) {
+		if (page[i] != 0) {
+			tst_res(TFAIL, "page[%d]=0x%x not zero", i, page[i]);
+			return;
+		}
+	}
+
+	tst_res(TPASS, "Pagefault handled with UFFDIO_ZEROPAGE");
+
+	SAFE_PTHREAD_JOIN(thr, NULL);
+	reset_pages();
+}
+
+static struct tst_test test = {
+	.test_all = run,
+};