Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1878 insertions, 0 deletions

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
new file mode 100644
index 000000000..297f250c1
--- /dev/null
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -0,0 +1,1878 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Stress userfaultfd syscall.
+ *
+ *  Copyright (C) 2015  Red Hat, Inc.
+ *
+ * This test allocates two virtual areas and bounces the physical
+ * memory across the two virtual areas (from area_src to area_dst)
+ * using userfaultfd.
+ *
+ * There are three threads running per CPU:
+ *
+ * 1) one per-CPU thread takes a per-page pthread_mutex in a random
+ *    page of the area_dst (while the physical page may still be in
+ *    area_src), and increments a per-page counter in the same page,
+ *    and checks its value against a verification region.
+ *
+ * 2) another per-CPU thread handles the userfaults generated by
+ *    thread 1 above. userfaultfd blocking reads or poll() modes are
+ *    exercised interleaved.
+ *
+ * 3) one last per-CPU thread transfers the memory in the background
+ *    at maximum bandwidth (if not already transferred by thread
+ *    2). Each cpu thread takes cares of transferring a portion of the
+ *    area.
+ *
+ * When all threads of type 3 completed the transfer, one bounce is
+ * complete. area_src and area_dst are then swapped. All threads are
+ * respawned and so the bounce is immediately restarted in the
+ * opposite direction.
+ *
+ * per-CPU threads 1 by triggering userfaults inside
+ * pthread_mutex_lock will also verify the atomicity of the memory
+ * transfer (UFFDIO_COPY).
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <time.h>
+#include <signal.h>
+#include <poll.h>
+#include <string.h>
+#include <linux/mman.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/wait.h>
+#include <pthread.h>
+#include <linux/userfaultfd.h>
+#include <setjmp.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <inttypes.h>
+#include <stdint.h>
+#include <sys/random.h>
+
+#include "../kselftest.h"
+#include "vm_util.h"
+
+#ifdef __NR_userfaultfd
+
+static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size, hpage_size;
+
+#define BOUNCE_RANDOM		(1<<0)
+#define BOUNCE_RACINGFAULTS	(1<<1)
+#define BOUNCE_VERIFY		(1<<2)
+#define BOUNCE_POLL		(1<<3)
+static int bounces;
+
+#define TEST_ANON	1
+#define TEST_HUGETLB	2
+#define TEST_SHMEM	3
+static int test_type;
+
+#define UFFD_FLAGS	(O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY)
+
+#define BASE_PMD_ADDR ((void *)(1UL << 30))
+
+/* test using /dev/userfaultfd, instead of userfaultfd(2) */
+static bool test_dev_userfaultfd;
+
+/* exercise the test_uffdio_*_eexist every ALARM_INTERVAL_SECS */
+#define ALARM_INTERVAL_SECS 10
+static volatile bool test_uffdio_copy_eexist = true;
+static volatile bool test_uffdio_zeropage_eexist = true;
+/* Whether to test uffd write-protection */
+static bool test_uffdio_wp = true;
+/* Whether to test uffd minor faults */
+static bool test_uffdio_minor = false;
+
+static bool map_shared;
+static int shm_fd;
+static int huge_fd;
+static unsigned long long *count_verify;
+static int uffd = -1;
+static int uffd_flags, finished, *pipefd;
+static char *area_src, *area_src_alias, *area_dst, *area_dst_alias, *area_remap;
+static char *zeropage;
+pthread_attr_t attr;
+static bool test_collapse;
+
+/* Userfaultfd test statistics */
+struct uffd_stats {
+	int cpu;
+	unsigned long missing_faults;
+	unsigned long wp_faults;
+	unsigned long minor_faults;
+};
+
+/* pthread_mutex_t starts at page offset 0 */
+#define area_mutex(___area, ___nr)					\
+	((pthread_mutex_t *) ((___area) + (___nr)*page_size))
+/*
+ * count is placed in the page after pthread_mutex_t naturally aligned
+ * to avoid non alignment faults on non-x86 archs.
+ */
+#define area_count(___area, ___nr)					\
+	((volatile unsigned long long *) ((unsigned long)		\
+				 ((___area) + (___nr)*page_size +	\
+				  sizeof(pthread_mutex_t) +		\
+				  sizeof(unsigned long long) - 1) &	\
+				 ~(unsigned long)(sizeof(unsigned long long) \
+						  -  1)))
+
+#define swap(a, b) \
+	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
+
+#define factor_of_2(x) ((x) ^ ((x) & ((x) - 1)))
+
+const char *examples =
+    "# Run anonymous memory test on 100MiB region with 99999 bounces:\n"
+    "./userfaultfd anon 100 99999\n\n"
+    "# Run the same anonymous memory test, but using /dev/userfaultfd:\n"
+    "./userfaultfd anon:dev 100 99999\n\n"
+    "# Run share memory test on 1GiB region with 99 bounces:\n"
+    "./userfaultfd shmem 1000 99\n\n"
+    "# Run hugetlb memory test on 256MiB region with 50 bounces:\n"
+    "./userfaultfd hugetlb 256 50\n\n"
+    "# Run the same hugetlb test but using shared file:\n"
+    "./userfaultfd hugetlb_shared 256 50 /dev/hugepages/hugefile\n\n"
+    "# 10MiB-~6GiB 999 bounces anonymous test, "
+    "continue forever unless an error triggers\n"
+    "while ./userfaultfd anon $[RANDOM % 6000 + 10] 999; do true; done\n\n";
+
+static void usage(void)
+{
+	fprintf(stderr, "\nUsage: ./userfaultfd <test type> <MiB> <bounces> "
+		"[hugetlbfs_file]\n\n");
+	fprintf(stderr, "Supported <test type>: anon, hugetlb, "
+		"hugetlb_shared, shmem\n\n");
+	fprintf(stderr, "'Test mods' can be joined to the test type string with a ':'. "
+		"Supported mods:\n");
+	fprintf(stderr, "\tsyscall - Use userfaultfd(2) (default)\n");
+	fprintf(stderr, "\tdev - Use /dev/userfaultfd instead of userfaultfd(2)\n");
+	fprintf(stderr, "\tcollapse - Test MADV_COLLAPSE of UFFDIO_REGISTER_MODE_MINOR\n"
+		"memory\n");
+	fprintf(stderr, "\nExample test mod usage:\n");
+	fprintf(stderr, "# Run anonymous memory test with /dev/userfaultfd:\n");
+	fprintf(stderr, "./userfaultfd anon:dev 100 99999\n\n");
+
+	fprintf(stderr, "Examples:\n\n");
+	fprintf(stderr, "%s", examples);
+	exit(1);
+}
+
+#define _err(fmt, ...)						\
+	do {							\
+		int ret = errno;				\
+		fprintf(stderr, "ERROR: " fmt, ##__VA_ARGS__);	\
+		fprintf(stderr, " (errno=%d, line=%d)\n",	\
+			ret, __LINE__);				\
+	} while (0)
+
+#define errexit(exitcode, fmt, ...)		\
+	do {					\
+		_err(fmt, ##__VA_ARGS__);	\
+		exit(exitcode);			\
+	} while (0)
+
+#define err(fmt, ...) errexit(1, fmt, ##__VA_ARGS__)
+
+static void uffd_stats_reset(struct uffd_stats *uffd_stats,
+			     unsigned long n_cpus)
+{
+	int i;
+
+	for (i = 0; i < n_cpus; i++) {
+		uffd_stats[i].cpu = i;
+		uffd_stats[i].missing_faults = 0;
+		uffd_stats[i].wp_faults = 0;
+		uffd_stats[i].minor_faults = 0;
+	}
+}
+
+static void uffd_stats_report(struct uffd_stats *stats, int n_cpus)
+{
+	int i;
+	unsigned long long miss_total = 0, wp_total = 0, minor_total = 0;
+
+	for (i = 0; i < n_cpus; i++) {
+		miss_total += stats[i].missing_faults;
+		wp_total += stats[i].wp_faults;
+		minor_total += stats[i].minor_faults;
+	}
+
+	printf("userfaults: ");
+	if (miss_total) {
+		printf("%llu missing (", miss_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", stats[i].missing_faults);
+		printf("\b) ");
+	}
+	if (wp_total) {
+		printf("%llu wp (", wp_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", stats[i].wp_faults);
+		printf("\b) ");
+	}
+	if (minor_total) {
+		printf("%llu minor (", minor_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", stats[i].minor_faults);
+		printf("\b)");
+	}
+	printf("\n");
+}
+
+static void anon_release_pages(char *rel_area)
+{
+	if (madvise(rel_area, nr_pages * page_size, MADV_DONTNEED))
+		err("madvise(MADV_DONTNEED) failed");
+}
+
+static void anon_allocate_area(void **alloc_area, bool is_src)
+{
+	*alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
+			   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+}
+
+static void noop_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+}
+
+static void hugetlb_release_pages(char *rel_area)
+{
+	if (!map_shared) {
+		if (madvise(rel_area, nr_pages * page_size, MADV_DONTNEED))
+			err("madvise(MADV_DONTNEED) failed");
+	} else {
+		if (madvise(rel_area, nr_pages * page_size, MADV_REMOVE))
+			err("madvise(MADV_REMOVE) failed");
+	}
+}
+
+static void hugetlb_allocate_area(void **alloc_area, bool is_src)
+{
+	void *area_alias = NULL;
+	char **alloc_area_alias;
+
+	if (!map_shared)
+		*alloc_area = mmap(NULL,
+			nr_pages * page_size,
+			PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB |
+				(is_src ? 0 : MAP_NORESERVE),
+			-1,
+			0);
+	else
+		*alloc_area = mmap(NULL,
+			nr_pages * page_size,
+			PROT_READ | PROT_WRITE,
+			MAP_SHARED |
+				(is_src ? 0 : MAP_NORESERVE),
+			huge_fd,
+			is_src ? 0 : nr_pages * page_size);
+	if (*alloc_area == MAP_FAILED)
+		err("mmap of hugetlbfs file failed");
+
+	if (map_shared) {
+		area_alias = mmap(NULL,
+			nr_pages * page_size,
+			PROT_READ | PROT_WRITE,
+			MAP_SHARED,
+			huge_fd,
+			is_src ? 0 : nr_pages * page_size);
+		if (area_alias == MAP_FAILED)
+			err("mmap of hugetlb file alias failed");
+	}
+
+	if (is_src) {
+		alloc_area_alias = &area_src_alias;
+	} else {
+		alloc_area_alias = &area_dst_alias;
+	}
+	if (area_alias)
+		*alloc_area_alias = area_alias;
+}
+
+static void hugetlb_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+	if (!map_shared)
+		return;
+
+	*start = (unsigned long) area_dst_alias + offset;
+}
+
+static void shmem_release_pages(char *rel_area)
+{
+	if (madvise(rel_area, nr_pages * page_size, MADV_REMOVE))
+		err("madvise(MADV_REMOVE) failed");
+}
+
+static void shmem_allocate_area(void **alloc_area, bool is_src)
+{
+	void *area_alias = NULL;
+	size_t bytes = nr_pages * page_size;
+	unsigned long offset = is_src ? 0 : bytes;
+	char *p = NULL, *p_alias = NULL;
+
+	if (test_collapse) {
+		p = BASE_PMD_ADDR;
+		if (!is_src)
+			/* src map + alias + interleaved hpages */
+			p += 2 * (bytes + hpage_size);
+		p_alias = p;
+		p_alias += bytes;
+		p_alias += hpage_size;  /* Prevent src/dst VMA merge */
+	}
+
+	*alloc_area = mmap(p, bytes, PROT_READ | PROT_WRITE, MAP_SHARED,
+			   shm_fd, offset);
+	if (*alloc_area == MAP_FAILED)
+		err("mmap of memfd failed");
+	if (test_collapse && *alloc_area != p)
+		err("mmap of memfd failed at %p", p);
+
+	area_alias = mmap(p_alias, bytes, PROT_READ | PROT_WRITE, MAP_SHARED,
+			  shm_fd, offset);
+	if (area_alias == MAP_FAILED)
+		err("mmap of memfd alias failed");
+	if (test_collapse && area_alias != p_alias)
+		err("mmap of anonymous memory failed at %p", p_alias);
+
+	if (is_src)
+		area_src_alias = area_alias;
+	else
+		area_dst_alias = area_alias;
+}
+
+static void shmem_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+	*start = (unsigned long)area_dst_alias + offset;
+}
+
+static void shmem_check_pmd_mapping(void *p, int expect_nr_hpages)
+{
+	if (!check_huge_shmem(area_dst_alias, expect_nr_hpages, hpage_size))
+		err("Did not find expected %d number of hugepages",
+		    expect_nr_hpages);
+}
+
+struct uffd_test_ops {
+	void (*allocate_area)(void **alloc_area, bool is_src);
+	void (*release_pages)(char *rel_area);
+	void (*alias_mapping)(__u64 *start, size_t len, unsigned long offset);
+	void (*check_pmd_mapping)(void *p, int expect_nr_hpages);
+};
+
+static struct uffd_test_ops anon_uffd_test_ops = {
+	.allocate_area	= anon_allocate_area,
+	.release_pages	= anon_release_pages,
+	.alias_mapping = noop_alias_mapping,
+	.check_pmd_mapping = NULL,
+};
+
+static struct uffd_test_ops shmem_uffd_test_ops = {
+	.allocate_area	= shmem_allocate_area,
+	.release_pages	= shmem_release_pages,
+	.alias_mapping = shmem_alias_mapping,
+	.check_pmd_mapping = shmem_check_pmd_mapping,
+};
+
+static struct uffd_test_ops hugetlb_uffd_test_ops = {
+	.allocate_area	= hugetlb_allocate_area,
+	.release_pages	= hugetlb_release_pages,
+	.alias_mapping = hugetlb_alias_mapping,
+	.check_pmd_mapping = NULL,
+};
+
+static struct uffd_test_ops *uffd_test_ops;
+
+static inline uint64_t uffd_minor_feature(void)
+{
+	if (test_type == TEST_HUGETLB && map_shared)
+		return UFFD_FEATURE_MINOR_HUGETLBFS;
+	else if (test_type == TEST_SHMEM)
+		return UFFD_FEATURE_MINOR_SHMEM;
+	else
+		return 0;
+}
+
+static uint64_t get_expected_ioctls(uint64_t mode)
+{
+	uint64_t ioctls = UFFD_API_RANGE_IOCTLS;
+
+	if (test_type == TEST_HUGETLB)
+		ioctls &= ~(1 << _UFFDIO_ZEROPAGE);
+
+	if (!((mode & UFFDIO_REGISTER_MODE_WP) && test_uffdio_wp))
+		ioctls &= ~(1 << _UFFDIO_WRITEPROTECT);
+
+	if (!((mode & UFFDIO_REGISTER_MODE_MINOR) && test_uffdio_minor))
+		ioctls &= ~(1 << _UFFDIO_CONTINUE);
+
+	return ioctls;
+}
+
+static void assert_expected_ioctls_present(uint64_t mode, uint64_t ioctls)
+{
+	uint64_t expected = get_expected_ioctls(mode);
+	uint64_t actual = ioctls & expected;
+
+	if (actual != expected) {
+		err("missing ioctl(s): expected %"PRIx64" actual: %"PRIx64,
+		    expected, actual);
+	}
+}
+
+static int __userfaultfd_open_dev(void)
+{
+	int fd, _uffd;
+
+	fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
+	if (fd < 0)
+		errexit(KSFT_SKIP, "opening /dev/userfaultfd failed");
+
+	_uffd = ioctl(fd, USERFAULTFD_IOC_NEW, UFFD_FLAGS);
+	if (_uffd < 0)
+		errexit(errno == ENOTTY ? KSFT_SKIP : 1,
+			"creating userfaultfd failed");
+	close(fd);
+	return _uffd;
+}
+
+static void userfaultfd_open(uint64_t *features)
+{
+	struct uffdio_api uffdio_api;
+
+	if (test_dev_userfaultfd)
+		uffd = __userfaultfd_open_dev();
+	else {
+		uffd = syscall(__NR_userfaultfd, UFFD_FLAGS);
+		if (uffd < 0)
+			errexit(errno == ENOSYS ? KSFT_SKIP : 1,
+				"creating userfaultfd failed");
+	}
+	uffd_flags = fcntl(uffd, F_GETFD, NULL);
+
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = *features;
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api))
+		err("UFFDIO_API failed.\nPlease make sure to "
+		    "run with either root or ptrace capability.");
+	if (uffdio_api.api != UFFD_API)
+		err("UFFDIO_API error: %" PRIu64, (uint64_t)uffdio_api.api);
+
+	*features = uffdio_api.features;
+}
+
+static inline void munmap_area(void **area)
+{
+	if (*area)
+		if (munmap(*area, nr_pages * page_size))
+			err("munmap");
+
+	*area = NULL;
+}
+
+static void uffd_test_ctx_clear(void)
+{
+	size_t i;
+
+	if (pipefd) {
+		for (i = 0; i < nr_cpus * 2; ++i) {
+			if (close(pipefd[i]))
+				err("close pipefd");
+		}
+		free(pipefd);
+		pipefd = NULL;
+	}
+
+	if (count_verify) {
+		free(count_verify);
+		count_verify = NULL;
+	}
+
+	if (uffd != -1) {
+		if (close(uffd))
+			err("close uffd");
+		uffd = -1;
+	}
+
+	munmap_area((void **)&area_src);
+	munmap_area((void **)&area_src_alias);
+	munmap_area((void **)&area_dst);
+	munmap_area((void **)&area_dst_alias);
+	munmap_area((void **)&area_remap);
+}
+
+static void uffd_test_ctx_init(uint64_t features)
+{
+	unsigned long nr, cpu;
+
+	uffd_test_ctx_clear();
+
+	uffd_test_ops->allocate_area((void **)&area_src, true);
+	uffd_test_ops->allocate_area((void **)&area_dst, false);
+
+	userfaultfd_open(&features);
+
+	count_verify = malloc(nr_pages * sizeof(unsigned long long));
+	if (!count_verify)
+		err("count_verify");
+
+	for (nr = 0; nr < nr_pages; nr++) {
+		*area_mutex(area_src, nr) =
+			(pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER;
+		count_verify[nr] = *area_count(area_src, nr) = 1;
+		/*
+		 * In the transition between 255 to 256, powerpc will
+		 * read out of order in my_bcmp and see both bytes as
+		 * zero, so leave a placeholder below always non-zero
+		 * after the count, to avoid my_bcmp to trigger false
+		 * positives.
+		 */
+		*(area_count(area_src, nr) + 1) = 1;
+	}
+
+	/*
+	 * After initialization of area_src, we must explicitly release pages
+	 * for area_dst to make sure it's fully empty.  Otherwise we could have
+	 * some area_dst pages be errornously initialized with zero pages,
+	 * hence we could hit memory corruption later in the test.
+	 *
+	 * One example is when THP is globally enabled, above allocate_area()
+	 * calls could have the two areas merged into a single VMA (as they
+	 * will have the same VMA flags so they're mergeable).  When we
+	 * initialize the area_src above, it's possible that some part of
+	 * area_dst could have been faulted in via one huge THP that will be
+	 * shared between area_src and area_dst.  It could cause some of the
+	 * area_dst won't be trapped by missing userfaults.
+	 *
+	 * This release_pages() will guarantee even if that happened, we'll
+	 * proactively split the thp and drop any accidentally initialized
+	 * pages within area_dst.
+	 */
+	uffd_test_ops->release_pages(area_dst);
+
+	pipefd = malloc(sizeof(int) * nr_cpus * 2);
+	if (!pipefd)
+		err("pipefd");
+	for (cpu = 0; cpu < nr_cpus; cpu++)
+		if (pipe2(&pipefd[cpu * 2], O_CLOEXEC | O_NONBLOCK))
+			err("pipe");
+}
+
+static int my_bcmp(char *str1, char *str2, size_t n)
+{
+	unsigned long i;
+	for (i = 0; i < n; i++)
+		if (str1[i] != str2[i])
+			return 1;
+	return 0;
+}
+
+static void wp_range(int ufd, __u64 start, __u64 len, bool wp)
+{
+	struct uffdio_writeprotect prms;
+
+	/* Write protection page faults */
+	prms.range.start = start;
+	prms.range.len = len;
+	/* Undo write-protect, do wakeup after that */
+	prms.mode = wp ? UFFDIO_WRITEPROTECT_MODE_WP : 0;
+
+	if (ioctl(ufd, UFFDIO_WRITEPROTECT, &prms))
+		err("clear WP failed: address=0x%"PRIx64, (uint64_t)start);
+}
+
+static void continue_range(int ufd, __u64 start, __u64 len)
+{
+	struct uffdio_continue req;
+	int ret;
+
+	req.range.start = start;
+	req.range.len = len;
+	req.mode = 0;
+
+	if (ioctl(ufd, UFFDIO_CONTINUE, &req))
+		err("UFFDIO_CONTINUE failed for address 0x%" PRIx64,
+		    (uint64_t)start);
+
+	/*
+	 * Error handling within the kernel for continue is subtly different
+	 * from copy or zeropage, so it may be a source of bugs. Trigger an
+	 * error (-EEXIST) on purpose, to verify doing so doesn't cause a BUG.
+	 */
+	req.mapped = 0;
+	ret = ioctl(ufd, UFFDIO_CONTINUE, &req);
+	if (ret >= 0 || req.mapped != -EEXIST)
+		err("failed to exercise UFFDIO_CONTINUE error handling, ret=%d, mapped=%" PRId64,
+		    ret, (int64_t) req.mapped);
+}
+
+static void *locking_thread(void *arg)
+{
+	unsigned long cpu = (unsigned long) arg;
+	unsigned long page_nr;
+	unsigned long long count;
+
+	if (!(bounces & BOUNCE_RANDOM)) {
+		page_nr = -bounces;
+		if (!(bounces & BOUNCE_RACINGFAULTS))
+			page_nr += cpu * nr_pages_per_cpu;
+	}
+
+	while (!finished) {
+		if (bounces & BOUNCE_RANDOM) {
+			if (getrandom(&page_nr, sizeof(page_nr), 0) != sizeof(page_nr))
+				err("getrandom failed");
+		} else
+			page_nr += 1;
+		page_nr %= nr_pages;
+		pthread_mutex_lock(area_mutex(area_dst, page_nr));
+		count = *area_count(area_dst, page_nr);
+		if (count != count_verify[page_nr])
+			err("page_nr %lu memory corruption %llu %llu",
+			    page_nr, count, count_verify[page_nr]);
+		count++;
+		*area_count(area_dst, page_nr) = count_verify[page_nr] = count;
+		pthread_mutex_unlock(area_mutex(area_dst, page_nr));
+	}
+
+	return NULL;
+}
+
+static void retry_copy_page(int ufd, struct uffdio_copy *uffdio_copy,
+			    unsigned long offset)
+{
+	uffd_test_ops->alias_mapping(&uffdio_copy->dst,
+				     uffdio_copy->len,
+				     offset);
+	if (ioctl(ufd, UFFDIO_COPY, uffdio_copy)) {
+		/* real retval in ufdio_copy.copy */
+		if (uffdio_copy->copy != -EEXIST)
+			err("UFFDIO_COPY retry error: %"PRId64,
+			    (int64_t)uffdio_copy->copy);
+	} else {
+		err("UFFDIO_COPY retry unexpected: %"PRId64,
+		    (int64_t)uffdio_copy->copy);
+	}
+}
+
+static void wake_range(int ufd, unsigned long addr, unsigned long len)
+{
+	struct uffdio_range uffdio_wake;
+
+	uffdio_wake.start = addr;
+	uffdio_wake.len = len;
+
+	if (ioctl(ufd, UFFDIO_WAKE, &uffdio_wake))
+		fprintf(stderr, "error waking %lu\n",
+			addr), exit(1);
+}
+
+static int __copy_page(int ufd, unsigned long offset, bool retry)
+{
+	struct uffdio_copy uffdio_copy;
+
+	if (offset >= nr_pages * page_size)
+		err("unexpected offset %lu\n", offset);
+	uffdio_copy.dst = (unsigned long) area_dst + offset;
+	uffdio_copy.src = (unsigned long) area_src + offset;
+	uffdio_copy.len = page_size;
+	if (test_uffdio_wp)
+		uffdio_copy.mode = UFFDIO_COPY_MODE_WP;
+	else
+		uffdio_copy.mode = 0;
+	uffdio_copy.copy = 0;
+	if (ioctl(ufd, UFFDIO_COPY, &uffdio_copy)) {
+		/* real retval in ufdio_copy.copy */
+		if (uffdio_copy.copy != -EEXIST)
+			err("UFFDIO_COPY error: %"PRId64,
+			    (int64_t)uffdio_copy.copy);
+		wake_range(ufd, uffdio_copy.dst, page_size);
+	} else if (uffdio_copy.copy != page_size) {
+		err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy);
+	} else {
+		if (test_uffdio_copy_eexist && retry) {
+			test_uffdio_copy_eexist = false;
+			retry_copy_page(ufd, &uffdio_copy, offset);
+		}
+		return 1;
+	}
+	return 0;
+}
+
+static int copy_page_retry(int ufd, unsigned long offset)
+{
+	return __copy_page(ufd, offset, true);
+}
+
+static int copy_page(int ufd, unsigned long offset)
+{
+	return __copy_page(ufd, offset, false);
+}
+
+static int uffd_read_msg(int ufd, struct uffd_msg *msg)
+{
+	int ret = read(uffd, msg, sizeof(*msg));
+
+	if (ret != sizeof(*msg)) {
+		if (ret < 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				return 1;
+			err("blocking read error");
+		} else {
+			err("short read");
+		}
+	}
+
+	return 0;
+}
+
+static void uffd_handle_page_fault(struct uffd_msg *msg,
+				   struct uffd_stats *stats)
+{
+	unsigned long offset;
+
+	if (msg->event != UFFD_EVENT_PAGEFAULT)
+		err("unexpected msg event %u", msg->event);
+
+	if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WP) {
+		/* Write protect page faults */
+		wp_range(uffd, msg->arg.pagefault.address, page_size, false);
+		stats->wp_faults++;
+	} else if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_MINOR) {
+		uint8_t *area;
+		int b;
+
+		/*
+		 * Minor page faults
+		 *
+		 * To prove we can modify the original range for testing
+		 * purposes, we're going to bit flip this range before
+		 * continuing.
+		 *
+		 * Note that this requires all minor page fault tests operate on
+		 * area_dst (non-UFFD-registered) and area_dst_alias
+		 * (UFFD-registered).
+		 */
+
+		area = (uint8_t *)(area_dst +
+				   ((char *)msg->arg.pagefault.address -
+				    area_dst_alias));
+		for (b = 0; b < page_size; ++b)
+			area[b] = ~area[b];
+		continue_range(uffd, msg->arg.pagefault.address, page_size);
+		stats->minor_faults++;
+	} else {
+		/*
+		 * Missing page faults.
+		 *
+		 * Here we force a write check for each of the missing mode
+		 * faults.  It's guaranteed because the only threads that
+		 * will trigger uffd faults are the locking threads, and
+		 * their first instruction to touch the missing page will
+		 * always be pthread_mutex_lock().
+		 *
+		 * Note that here we relied on an NPTL glibc impl detail to
+		 * always read the lock type at the entry of the lock op
+		 * (pthread_mutex_t.__data.__type, offset 0x10) before
+		 * doing any locking operations to guarantee that.  It's
+		 * actually not good to rely on this impl detail because
+		 * logically a pthread-compatible lib can implement the
+		 * locks without types and we can fail when linking with
+		 * them.  However since we used to find bugs with this
+		 * strict check we still keep it around.  Hopefully this
+		 * could be a good hint when it fails again.  If one day
+		 * it'll break on some other impl of glibc we'll revisit.
+		 */
+		if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
+			err("unexpected write fault");
+
+		offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
+		offset &= ~(page_size-1);
+
+		if (copy_page(uffd, offset))
+			stats->missing_faults++;
+	}
+}
+
+static void *uffd_poll_thread(void *arg)
+{
+	struct uffd_stats *stats = (struct uffd_stats *)arg;
+	unsigned long cpu = stats->cpu;
+	struct pollfd pollfd[2];
+	struct uffd_msg msg;
+	struct uffdio_register uffd_reg;
+	int ret;
+	char tmp_chr;
+
+	pollfd[0].fd = uffd;
+	pollfd[0].events = POLLIN;
+	pollfd[1].fd = pipefd[cpu*2];
+	pollfd[1].events = POLLIN;
+
+	for (;;) {
+		ret = poll(pollfd, 2, -1);
+		if (ret <= 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
+			err("poll error: %d", ret);
+		}
+		if (pollfd[1].revents & POLLIN) {
+			if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
+				err("read pipefd error");
+			break;
+		}
+		if (!(pollfd[0].revents & POLLIN))
+			err("pollfd[0].revents %d", pollfd[0].revents);
+		if (uffd_read_msg(uffd, &msg))
+			continue;
+		switch (msg.event) {
+		default:
+			err("unexpected msg event %u\n", msg.event);
+			break;
+		case UFFD_EVENT_PAGEFAULT:
+			uffd_handle_page_fault(&msg, stats);
+			break;
+		case UFFD_EVENT_FORK:
+			close(uffd);
+			uffd = msg.arg.fork.ufd;
+			pollfd[0].fd = uffd;
+			break;
+		case UFFD_EVENT_REMOVE:
+			uffd_reg.range.start = msg.arg.remove.start;
+			uffd_reg.range.len = msg.arg.remove.end -
+				msg.arg.remove.start;
+			if (ioctl(uffd, UFFDIO_UNREGISTER, &uffd_reg.range))
+				err("remove failure");
+			break;
+		case UFFD_EVENT_REMAP:
+			area_remap = area_dst;  /* save for later unmap */
+			area_dst = (char *)(unsigned long)msg.arg.remap.to;
+			break;
+		}
+	}
+
+	return NULL;
+}
+
+pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+static void *uffd_read_thread(void *arg)
+{
+	struct uffd_stats *stats = (struct uffd_stats *)arg;
+	struct uffd_msg msg;
+
+	pthread_mutex_unlock(&uffd_read_mutex);
+	/* from here cancellation is ok */
+
+	for (;;) {
+		if (uffd_read_msg(uffd, &msg))
+			continue;
+		uffd_handle_page_fault(&msg, stats);
+	}
+
+	return NULL;
+}
+
+static void *background_thread(void *arg)
+{
+	unsigned long cpu = (unsigned long) arg;
+	unsigned long page_nr, start_nr, mid_nr, end_nr;
+
+	start_nr = cpu * nr_pages_per_cpu;
+	end_nr = (cpu+1) * nr_pages_per_cpu;
+	mid_nr = (start_nr + end_nr) / 2;
+
+	/* Copy the first half of the pages */
+	for (page_nr = start_nr; page_nr < mid_nr; page_nr++)
+		copy_page_retry(uffd, page_nr * page_size);
+
+	/*
+	 * If we need to test uffd-wp, set it up now.  Then we'll have
+	 * at least the first half of the pages mapped already which
+	 * can be write-protected for testing
+	 */
+	if (test_uffdio_wp)
+		wp_range(uffd, (unsigned long)area_dst + start_nr * page_size,
+			nr_pages_per_cpu * page_size, true);
+
+	/*
+	 * Continue the 2nd half of the page copying, handling write
+	 * protection faults if any
+	 */
+	for (page_nr = mid_nr; page_nr < end_nr; page_nr++)
+		copy_page_retry(uffd, page_nr * page_size);
+
+	return NULL;
+}
+
+static int stress(struct uffd_stats *uffd_stats)
+{
+	unsigned long cpu;
+	pthread_t locking_threads[nr_cpus];
+	pthread_t uffd_threads[nr_cpus];
+	pthread_t background_threads[nr_cpus];
+
+	finished = 0;
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		if (pthread_create(&locking_threads[cpu], &attr,
+				   locking_thread, (void *)cpu))
+			return 1;
+		if (bounces & BOUNCE_POLL) {
+			if (pthread_create(&uffd_threads[cpu], &attr,
+					   uffd_poll_thread,
+					   (void *)&uffd_stats[cpu]))
+				return 1;
+		} else {
+			if (pthread_create(&uffd_threads[cpu], &attr,
+					   uffd_read_thread,
+					   (void *)&uffd_stats[cpu]))
+				return 1;
+			pthread_mutex_lock(&uffd_read_mutex);
+		}
+		if (pthread_create(&background_threads[cpu], &attr,
+				   background_thread, (void *)cpu))
+			return 1;
+	}
+	for (cpu = 0; cpu < nr_cpus; cpu++)
+		if (pthread_join(background_threads[cpu], NULL))
+			return 1;
+
+	/*
+	 * Be strict and immediately zap area_src, the whole area has
+	 * been transferred already by the background treads. The
+	 * area_src could then be faulted in a racy way by still
+	 * running uffdio_threads reading zeropages after we zapped
+	 * area_src (but they're guaranteed to get -EEXIST from
+	 * UFFDIO_COPY without writing zero pages into area_dst
+	 * because the background threads already completed).
+	 */
+	uffd_test_ops->release_pages(area_src);
+
+	finished = 1;
+	for (cpu = 0; cpu < nr_cpus; cpu++)
+		if (pthread_join(locking_threads[cpu], NULL))
+			return 1;
+
+	for (cpu = 0; cpu < nr_cpus; cpu++) {
+		char c;
+		if (bounces & BOUNCE_POLL) {
+			if (write(pipefd[cpu*2+1], &c, 1) != 1)
+				err("pipefd write error");
+			if (pthread_join(uffd_threads[cpu],
+					 (void *)&uffd_stats[cpu]))
+				return 1;
+		} else {
+			if (pthread_cancel(uffd_threads[cpu]))
+				return 1;
+			if (pthread_join(uffd_threads[cpu], NULL))
+				return 1;
+		}
+	}
+
+	return 0;
+}
+
+sigjmp_buf jbuf, *sigbuf;
+
+static void sighndl(int sig, siginfo_t *siginfo, void *ptr)
+{
+	if (sig == SIGBUS) {
+		if (sigbuf)
+			siglongjmp(*sigbuf, 1);
+		abort();
+	}
+}
+
+/*
+ * For non-cooperative userfaultfd test we fork() a process that will
+ * generate pagefaults, will mremap the area monitored by the
+ * userfaultfd and at last this process will release the monitored
+ * area.
+ * For the anonymous and shared memory the area is divided into two
+ * parts, the first part is accessed before mremap, and the second
+ * part is accessed after mremap. Since hugetlbfs does not support
+ * mremap, the entire monitored area is accessed in a single pass for
+ * HUGETLB_TEST.
+ * The release of the pages currently generates event for shmem and
+ * anonymous memory (UFFD_EVENT_REMOVE), hence it is not checked
+ * for hugetlb.
+ * For signal test(UFFD_FEATURE_SIGBUS), signal_test = 1, we register
+ * monitored area, generate pagefaults and test that signal is delivered.
+ * Use UFFDIO_COPY to allocate missing page and retry. For signal_test = 2
+ * test robustness use case - we release monitored area, fork a process
+ * that will generate pagefaults and verify signal is generated.
+ * This also tests UFFD_FEATURE_EVENT_FORK event along with the signal
+ * feature. Using monitor thread, verify no userfault events are generated.
+ */
+static int faulting_process(int signal_test)
+{
+	unsigned long nr;
+	unsigned long long count;
+	unsigned long split_nr_pages;
+	unsigned long lastnr;
+	struct sigaction act;
+	volatile unsigned long signalled = 0;
+
+	split_nr_pages = (nr_pages + 1) / 2;
+
+	if (signal_test) {
+		sigbuf = &jbuf;
+		memset(&act, 0, sizeof(act));
+		act.sa_sigaction = sighndl;
+		act.sa_flags = SA_SIGINFO;
+		if (sigaction(SIGBUS, &act, 0))
+			err("sigaction");
+		lastnr = (unsigned long)-1;
+	}
+
+	for (nr = 0; nr < split_nr_pages; nr++) {
+		volatile int steps = 1;
+		unsigned long offset = nr * page_size;
+
+		if (signal_test) {
+			if (sigsetjmp(*sigbuf, 1) != 0) {
+				if (steps == 1 && nr == lastnr)
+					err("Signal repeated");
+
+				lastnr = nr;
+				if (signal_test == 1) {
+					if (steps == 1) {
+						/* This is a MISSING request */
+						steps++;
+						if (copy_page(uffd, offset))
+							signalled++;
+					} else {
+						/* This is a WP request */
+						assert(steps == 2);
+						wp_range(uffd,
+							 (__u64)area_dst +
+							 offset,
+							 page_size, false);
+					}
+				} else {
+					signalled++;
+					continue;
+				}
+			}
+		}
+
+		count = *area_count(area_dst, nr);
+		if (count != count_verify[nr])
+			err("nr %lu memory corruption %llu %llu\n",
+			    nr, count, count_verify[nr]);
+		/*
+		 * Trigger write protection if there is by writing
+		 * the same value back.
+		 */
+		*area_count(area_dst, nr) = count;
+	}
+
+	if (signal_test)
+		return signalled != split_nr_pages;
+
+	area_dst = mremap(area_dst, nr_pages * page_size,  nr_pages * page_size,
+			  MREMAP_MAYMOVE | MREMAP_FIXED, area_src);
+	if (area_dst == MAP_FAILED)
+		err("mremap");
+	/* Reset area_src since we just clobbered it */
+	area_src = NULL;
+
+	for (; nr < nr_pages; nr++) {
+		count = *area_count(area_dst, nr);
+		if (count != count_verify[nr]) {
+			err("nr %lu memory corruption %llu %llu\n",
+			    nr, count, count_verify[nr]);
+		}
+		/*
+		 * Trigger write protection if there is by writing
+		 * the same value back.
+		 */
+		*area_count(area_dst, nr) = count;
+	}
+
+	uffd_test_ops->release_pages(area_dst);
+
+	for (nr = 0; nr < nr_pages; nr++)
+		if (my_bcmp(area_dst + nr * page_size, zeropage, page_size))
+			err("nr %lu is not zero", nr);
+
+	return 0;
+}
+
+static void retry_uffdio_zeropage(int ufd,
+				  struct uffdio_zeropage *uffdio_zeropage,
+				  unsigned long offset)
+{
+	uffd_test_ops->alias_mapping(&uffdio_zeropage->range.start,
+				     uffdio_zeropage->range.len,
+				     offset);
+	if (ioctl(ufd, UFFDIO_ZEROPAGE, uffdio_zeropage)) {
+		if (uffdio_zeropage->zeropage != -EEXIST)
+			err("UFFDIO_ZEROPAGE error: %"PRId64,
+			    (int64_t)uffdio_zeropage->zeropage);
+	} else {
+		err("UFFDIO_ZEROPAGE error: %"PRId64,
+		    (int64_t)uffdio_zeropage->zeropage);
+	}
+}
+
+static int __uffdio_zeropage(int ufd, unsigned long offset, bool retry)
+{
+	struct uffdio_zeropage uffdio_zeropage;
+	int ret;
+	bool has_zeropage = get_expected_ioctls(0) & (1 << _UFFDIO_ZEROPAGE);
+	__s64 res;
+
+	if (offset >= nr_pages * page_size)
+		err("unexpected offset %lu", offset);
+	uffdio_zeropage.range.start = (unsigned long) area_dst + offset;
+	uffdio_zeropage.range.len = page_size;
+	uffdio_zeropage.mode = 0;
+	ret = ioctl(ufd, UFFDIO_ZEROPAGE, &uffdio_zeropage);
+	res = uffdio_zeropage.zeropage;
+	if (ret) {
+		/* real retval in ufdio_zeropage.zeropage */
+		if (has_zeropage)
+			err("UFFDIO_ZEROPAGE error: %"PRId64, (int64_t)res);
+		else if (res != -EINVAL)
+			err("UFFDIO_ZEROPAGE not -EINVAL");
+	} else if (has_zeropage) {
+		if (res != page_size) {
+			err("UFFDIO_ZEROPAGE unexpected size");
+		} else {
+			if (test_uffdio_zeropage_eexist && retry) {
+				test_uffdio_zeropage_eexist = false;
+				retry_uffdio_zeropage(ufd, &uffdio_zeropage,
+						      offset);
+			}
+			return 1;
+		}
+	} else
+		err("UFFDIO_ZEROPAGE succeeded");
+
+	return 0;
+}
+
+static int uffdio_zeropage(int ufd, unsigned long offset)
+{
+	return __uffdio_zeropage(ufd, offset, false);
+}
+
+/* exercise UFFDIO_ZEROPAGE */
+static int userfaultfd_zeropage_test(void)
+{
+	struct uffdio_register uffdio_register;
+
+	printf("testing UFFDIO_ZEROPAGE: ");
+	fflush(stdout);
+
+	uffd_test_ctx_init(0);
+
+	uffdio_register.range.start = (unsigned long) area_dst;
+	uffdio_register.range.len = nr_pages * page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+	if (test_uffdio_wp)
+		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		err("register failure");
+
+	assert_expected_ioctls_present(
+		uffdio_register.mode, uffdio_register.ioctls);
+
+	if (uffdio_zeropage(uffd, 0))
+		if (my_bcmp(area_dst, zeropage, page_size))
+			err("zeropage is not zero");
+
+	printf("done.\n");
+	return 0;
+}
+
+static int userfaultfd_events_test(void)
+{
+	struct uffdio_register uffdio_register;
+	pthread_t uffd_mon;
+	int err, features;
+	pid_t pid;
+	char c;
+	struct uffd_stats stats = { 0 };
+
+	printf("testing events (fork, remap, remove): ");
+	fflush(stdout);
+
+	features = UFFD_FEATURE_EVENT_FORK | UFFD_FEATURE_EVENT_REMAP |
+		UFFD_FEATURE_EVENT_REMOVE;
+	uffd_test_ctx_init(features);
+
+	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
+
+	uffdio_register.range.start = (unsigned long) area_dst;
+	uffdio_register.range.len = nr_pages * page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+	if (test_uffdio_wp)
+		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		err("register failure");
+
+	assert_expected_ioctls_present(
+		uffdio_register.mode, uffdio_register.ioctls);
+
+	if (pthread_create(&uffd_mon, &attr, uffd_poll_thread, &stats))
+		err("uffd_poll_thread create");
+
+	pid = fork();
+	if (pid < 0)
+		err("fork");
+
+	if (!pid)
+		exit(faulting_process(0));
+
+	waitpid(pid, &err, 0);
+	if (err)
+		err("faulting process failed");
+	if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
+		err("pipe write");
+	if (pthread_join(uffd_mon, NULL))
+		return 1;
+
+	uffd_stats_report(&stats, 1);
+
+	return stats.missing_faults != nr_pages;
+}
+
+static int userfaultfd_sig_test(void)
+{
+	struct uffdio_register uffdio_register;
+	unsigned long userfaults;
+	pthread_t uffd_mon;
+	int err, features;
+	pid_t pid;
+	char c;
+	struct uffd_stats stats = { 0 };
+
+	printf("testing signal delivery: ");
+	fflush(stdout);
+
+	features = UFFD_FEATURE_EVENT_FORK|UFFD_FEATURE_SIGBUS;
+	uffd_test_ctx_init(features);
+
+	fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
+
+	uffdio_register.range.start = (unsigned long) area_dst;
+	uffdio_register.range.len = nr_pages * page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+	if (test_uffdio_wp)
+		uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		err("register failure");
+
+	assert_expected_ioctls_present(
+		uffdio_register.mode, uffdio_register.ioctls);
+
+	if (faulting_process(1))
+		err("faulting process failed");
+
+	uffd_test_ops->release_pages(area_dst);
+
+	if (pthread_create(&uffd_mon, &attr, uffd_poll_thread, &stats))
+		err("uffd_poll_thread create");
+
+	pid = fork();
+	if (pid < 0)
+		err("fork");
+
+	if (!pid)
+		exit(faulting_process(2));
+
+	waitpid(pid, &err, 0);
+	if (err)
+		err("faulting process failed");
+	if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
+		err("pipe write");
+	if (pthread_join(uffd_mon, (void **)&userfaults))
+		return 1;
+
+	printf("done.\n");
+	if (userfaults)
+		err("Signal test failed, userfaults: %ld", userfaults);
+
+	return userfaults != 0;
+}
+
+void check_memory_contents(char *p)
+{
+	unsigned long i;
+	uint8_t expected_byte;
+	void *expected_page;
+
+	if (posix_memalign(&expected_page, page_size, page_size))
+		err("out of memory");
+
+	for (i = 0; i < nr_pages; ++i) {
+		expected_byte = ~((uint8_t)(i % ((uint8_t)-1)));
+		memset(expected_page, expected_byte, page_size);
+		if (my_bcmp(expected_page, p + (i * page_size), page_size))
+			err("unexpected page contents after minor fault");
+	}
+
+	free(expected_page);
+}
+
+static int userfaultfd_minor_test(void)
+{
+	unsigned long p;
+	struct uffdio_register uffdio_register;
+	pthread_t uffd_mon;
+	char c;
+	struct uffd_stats stats = { 0 };
+
+	if (!test_uffdio_minor)
+		return 0;
+
+	printf("testing minor faults: ");
+	fflush(stdout);
+
+	uffd_test_ctx_init(uffd_minor_feature());
+
+	uffdio_register.range.start = (unsigned long)area_dst_alias;
+	uffdio_register.range.len = nr_pages * page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MINOR;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		err("register failure");
+
+	assert_expected_ioctls_present(
+		uffdio_register.mode, uffdio_register.ioctls);
+
+	/*
+	 * After registering with UFFD, populate the non-UFFD-registered side of
+	 * the shared mapping. This should *not* trigger any UFFD minor faults.
+	 */
+	for (p = 0; p < nr_pages; ++p) {
+		memset(area_dst + (p * page_size), p % ((uint8_t)-1),
+		       page_size);
+	}
+
+	if (pthread_create(&uffd_mon, &attr, uffd_poll_thread, &stats))
+		err("uffd_poll_thread create");
+
+	/*
+	 * Read each of the pages back using the UFFD-registered mapping. We
+	 * expect that the first time we touch a page, it will result in a minor
+	 * fault. uffd_poll_thread will resolve the fault by bit-flipping the
+	 * page's contents, and then issuing a CONTINUE ioctl.
+	 */
+	check_memory_contents(area_dst_alias);
+
+	if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
+		err("pipe write");
+	if (pthread_join(uffd_mon, NULL))
+		return 1;
+
+	uffd_stats_report(&stats, 1);
+
+	if (test_collapse) {
+		printf("testing collapse of uffd memory into PMD-mapped THPs:");
+		if (madvise(area_dst_alias, nr_pages * page_size,
+			    MADV_COLLAPSE))
+			err("madvise(MADV_COLLAPSE)");
+
+		uffd_test_ops->check_pmd_mapping(area_dst,
+						 nr_pages * page_size /
+						 hpage_size);
+		/*
+		 * This won't cause uffd-fault - it purely just makes sure there
+		 * was no corruption.
+		 */
+		check_memory_contents(area_dst_alias);
+		printf(" done.\n");
+	}
+
+	return stats.missing_faults != 0 || stats.minor_faults != nr_pages;
+}
+
+#define BIT_ULL(nr)                   (1ULL << (nr))
+#define PM_SOFT_DIRTY                 BIT_ULL(55)
+#define PM_MMAP_EXCLUSIVE             BIT_ULL(56)
+#define PM_UFFD_WP                    BIT_ULL(57)
+#define PM_FILE                       BIT_ULL(61)
+#define PM_SWAP                       BIT_ULL(62)
+#define PM_PRESENT                    BIT_ULL(63)
+
+static int pagemap_open(void)
+{
+	int fd = open("/proc/self/pagemap", O_RDONLY);
+
+	if (fd < 0)
+		err("open pagemap");
+
+	return fd;
+}
+
+static uint64_t pagemap_read_vaddr(int fd, void *vaddr)
+{
+	uint64_t value;
+	int ret;
+
+	ret = pread(fd, &value, sizeof(uint64_t),
+		    ((uint64_t)vaddr >> 12) * sizeof(uint64_t));
+	if (ret != sizeof(uint64_t))
+		err("pread() on pagemap failed");
+
+	return value;
+}
+
+/* This macro let __LINE__ works in err() */
+#define  pagemap_check_wp(value, wp) do {				\
+		if (!!(value & PM_UFFD_WP) != wp)			\
+			err("pagemap uffd-wp bit error: 0x%"PRIx64, value); \
+	} while (0)
+
+static int pagemap_test_fork(bool present)
+{
+	pid_t child = fork();
+	uint64_t value;
+	int fd, result;
+
+	if (!child) {
+		/* Open the pagemap fd of the child itself */
+		fd = pagemap_open();
+		value = pagemap_read_vaddr(fd, area_dst);
+		/*
+		 * After fork() uffd-wp bit should be gone as long as we're
+		 * without UFFD_FEATURE_EVENT_FORK
+		 */
+		pagemap_check_wp(value, false);
+		/* Succeed */
+		exit(0);
+	}
+	waitpid(child, &result, 0);
+	return result;
+}
+
+static void userfaultfd_pagemap_test(unsigned int test_pgsize)
+{
+	struct uffdio_register uffdio_register;
+	int pagemap_fd;
+	uint64_t value;
+
+	/* Pagemap tests uffd-wp only */
+	if (!test_uffdio_wp)
+		return;
+
+	/* Not enough memory to test this page size */
+	if (test_pgsize > nr_pages * page_size)
+		return;
+
+	printf("testing uffd-wp with pagemap (pgsize=%u): ", test_pgsize);
+	/* Flush so it doesn't flush twice in parent/child later */
+	fflush(stdout);
+
+	uffd_test_ctx_init(0);
+
+	if (test_pgsize > page_size) {
+		/* This is a thp test */
+		if (madvise(area_dst, nr_pages * page_size, MADV_HUGEPAGE))
+			err("madvise(MADV_HUGEPAGE) failed");
+	} else if (test_pgsize == page_size) {
+		/* This is normal page test; force no thp */
+		if (madvise(area_dst, nr_pages * page_size, MADV_NOHUGEPAGE))
+			err("madvise(MADV_NOHUGEPAGE) failed");
+	}
+
+	uffdio_register.range.start = (unsigned long) area_dst;
+	uffdio_register.range.len = nr_pages * page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_WP;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+		err("register failed");
+
+	pagemap_fd = pagemap_open();
+
+	/* Touch the page */
+	*area_dst = 1;
+	wp_range(uffd, (uint64_t)area_dst, test_pgsize, true);
+	value = pagemap_read_vaddr(pagemap_fd, area_dst);
+	pagemap_check_wp(value, true);
+	/* Make sure uffd-wp bit dropped when fork */
+	if (pagemap_test_fork(true))
+		err("Detected stall uffd-wp bit in child");
+
+	/* Exclusive required or PAGEOUT won't work */
+	if (!(value & PM_MMAP_EXCLUSIVE))
+		err("multiple mapping detected: 0x%"PRIx64, value);
+
+	if (madvise(area_dst, test_pgsize, MADV_PAGEOUT))
+		err("madvise(MADV_PAGEOUT) failed");
+
+	/* Uffd-wp should persist even swapped out */
+	value = pagemap_read_vaddr(pagemap_fd, area_dst);
+	pagemap_check_wp(value, true);
+	/* Make sure uffd-wp bit dropped when fork */
+	if (pagemap_test_fork(false))
+		err("Detected stall uffd-wp bit in child");
+
+	/* Unprotect; this tests swap pte modifications */
+	wp_range(uffd, (uint64_t)area_dst, page_size, false);
+	value = pagemap_read_vaddr(pagemap_fd, area_dst);
+	pagemap_check_wp(value, false);
+
+	/* Fault in the page from disk */
+	*area_dst = 2;
+	value = pagemap_read_vaddr(pagemap_fd, area_dst);
+	pagemap_check_wp(value, false);
+
+	close(pagemap_fd);
+	printf("done\n");
+}
+
+static int userfaultfd_stress(void)
+{
+	void *area;
+	unsigned long nr;
+	struct uffdio_register uffdio_register;
+	struct uffd_stats uffd_stats[nr_cpus];
+
+	uffd_test_ctx_init(0);
+
+	if (posix_memalign(&area, page_size, page_size))
+		err("out of memory");
+	zeropage = area;
+	bzero(zeropage, page_size);
+
+	pthread_mutex_lock(&uffd_read_mutex);
+
+	pthread_attr_init(&attr);
+	pthread_attr_setstacksize(&attr, 16*1024*1024);
+
+	while (bounces--) {
+		printf("bounces: %d, mode:", bounces);
+		if (bounces & BOUNCE_RANDOM)
+			printf(" rnd");
+		if (bounces & BOUNCE_RACINGFAULTS)
+			printf(" racing");
+		if (bounces & BOUNCE_VERIFY)
+			printf(" ver");
+		if (bounces & BOUNCE_POLL)
+			printf(" poll");
+		else
+			printf(" read");
+		printf(", ");
+		fflush(stdout);
+
+		if (bounces & BOUNCE_POLL)
+			fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
+		else
+			fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
+
+		/* register */
+		uffdio_register.range.start = (unsigned long) area_dst;
+		uffdio_register.range.len = nr_pages * page_size;
+		uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+		if (test_uffdio_wp)
+			uffdio_register.mode |= UFFDIO_REGISTER_MODE_WP;
+		if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+			err("register failure");
+		assert_expected_ioctls_present(
+			uffdio_register.mode, uffdio_register.ioctls);
+
+		if (area_dst_alias) {
+			uffdio_register.range.start = (unsigned long)
+				area_dst_alias;
+			if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register))
+				err("register failure alias");
+		}
+
+		/*
+		 * The madvise done previously isn't enough: some
+		 * uffd_thread could have read userfaults (one of
+		 * those already resolved by the background thread)
+		 * and it may be in the process of calling
+		 * UFFDIO_COPY. UFFDIO_COPY will read the zapped
+		 * area_src and it would map a zero page in it (of
+		 * course such a UFFDIO_COPY is perfectly safe as it'd
+		 * return -EEXIST). The problem comes at the next
+		 * bounce though: that racing UFFDIO_COPY would
+		 * generate zeropages in the area_src, so invalidating
+		 * the previous MADV_DONTNEED. Without this additional
+		 * MADV_DONTNEED those zeropages leftovers in the
+		 * area_src would lead to -EEXIST failure during the
+		 * next bounce, effectively leaving a zeropage in the
+		 * area_dst.
+		 *
+		 * Try to comment this out madvise to see the memory
+		 * corruption being caught pretty quick.
+		 *
+		 * khugepaged is also inhibited to collapse THP after
+		 * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
+		 * required to MADV_DONTNEED here.
+		 */
+		uffd_test_ops->release_pages(area_dst);
+
+		uffd_stats_reset(uffd_stats, nr_cpus);
+
+		/* bounce pass */
+		if (stress(uffd_stats))
+			return 1;
+
+		/* Clear all the write protections if there is any */
+		if (test_uffdio_wp)
+			wp_range(uffd, (unsigned long)area_dst,
+				 nr_pages * page_size, false);
+
+		/* unregister */
+		if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range))
+			err("unregister failure");
+		if (area_dst_alias) {
+			uffdio_register.range.start = (unsigned long) area_dst;
+			if (ioctl(uffd, UFFDIO_UNREGISTER,
+				  &uffdio_register.range))
+				err("unregister failure alias");
+		}
+
+		/* verification */
+		if (bounces & BOUNCE_VERIFY)
+			for (nr = 0; nr < nr_pages; nr++)
+				if (*area_count(area_dst, nr) != count_verify[nr])
+					err("error area_count %llu %llu %lu\n",
+					    *area_count(area_src, nr),
+					    count_verify[nr], nr);
+
+		/* prepare next bounce */
+		swap(area_src, area_dst);
+
+		swap(area_src_alias, area_dst_alias);
+
+		uffd_stats_report(uffd_stats, nr_cpus);
+	}
+
+	if (test_type == TEST_ANON) {
+		/*
+		 * shmem/hugetlb won't be able to run since they have different
+		 * behavior on fork() (file-backed memory normally drops ptes
+		 * directly when fork), meanwhile the pagemap test will verify
+		 * pgtable entry of fork()ed child.
+		 */
+		userfaultfd_pagemap_test(page_size);
+		/*
+		 * Hard-code for x86_64 for now for 2M THP, as x86_64 is
+		 * currently the only one that supports uffd-wp
+		 */
+		userfaultfd_pagemap_test(page_size * 512);
+	}
+
+	return userfaultfd_zeropage_test() || userfaultfd_sig_test()
+		|| userfaultfd_events_test() || userfaultfd_minor_test();
+}
+
+/*
+ * Copied from mlock2-tests.c
+ */
+unsigned long default_huge_page_size(void)
+{
+	unsigned long hps = 0;
+	char *line = NULL;
+	size_t linelen = 0;
+	FILE *f = fopen("/proc/meminfo", "r");
+
+	if (!f)
+		return 0;
+	while (getline(&line, &linelen, f) > 0) {
+		if (sscanf(line, "Hugepagesize:       %lu kB", &hps) == 1) {
+			hps <<= 10;
+			break;
+		}
+	}
+
+	free(line);
+	fclose(f);
+	return hps;
+}
+
+static void set_test_type(const char *type)
+{
+	if (!strcmp(type, "anon")) {
+		test_type = TEST_ANON;
+		uffd_test_ops = &anon_uffd_test_ops;
+	} else if (!strcmp(type, "hugetlb")) {
+		test_type = TEST_HUGETLB;
+		uffd_test_ops = &hugetlb_uffd_test_ops;
+	} else if (!strcmp(type, "hugetlb_shared")) {
+		map_shared = true;
+		test_type = TEST_HUGETLB;
+		uffd_test_ops = &hugetlb_uffd_test_ops;
+		/* Minor faults require shared hugetlb; only enable here. */
+		test_uffdio_minor = true;
+	} else if (!strcmp(type, "shmem")) {
+		map_shared = true;
+		test_type = TEST_SHMEM;
+		uffd_test_ops = &shmem_uffd_test_ops;
+		test_uffdio_minor = true;
+	}
+}
+
+static void parse_test_type_arg(const char *raw_type)
+{
+	char *buf = strdup(raw_type);
+	uint64_t features = UFFD_API_FEATURES;
+
+	while (buf) {
+		const char *token = strsep(&buf, ":");
+
+		if (!test_type)
+			set_test_type(token);
+		else if (!strcmp(token, "dev"))
+			test_dev_userfaultfd = true;
+		else if (!strcmp(token, "syscall"))
+			test_dev_userfaultfd = false;
+		else if (!strcmp(token, "collapse"))
+			test_collapse = true;
+		else
+			err("unrecognized test mod '%s'", token);
+	}
+
+	if (!test_type)
+		err("failed to parse test type argument: '%s'", raw_type);
+
+	if (test_collapse && test_type != TEST_SHMEM)
+		err("Unsupported test: %s", raw_type);
+
+	if (test_type == TEST_HUGETLB)
+		page_size = hpage_size;
+	else
+		page_size = sysconf(_SC_PAGE_SIZE);
+
+	if (!page_size)
+		err("Unable to determine page size");
+	if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) * 2
+	    > page_size)
+		err("Impossible to run this test");
+
+	/*
+	 * Whether we can test certain features depends not just on test type,
+	 * but also on whether or not this particular kernel supports the
+	 * feature.
+	 */
+
+	userfaultfd_open(&features);
+
+	test_uffdio_wp = test_uffdio_wp &&
+		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
+	test_uffdio_minor = test_uffdio_minor &&
+		(features & uffd_minor_feature());
+
+	close(uffd);
+	uffd = -1;
+}
+
+static void sigalrm(int sig)
+{
+	if (sig != SIGALRM)
+		abort();
+	test_uffdio_copy_eexist = true;
+	test_uffdio_zeropage_eexist = true;
+	alarm(ALARM_INTERVAL_SECS);
+}
+
+int main(int argc, char **argv)
+{
+	size_t bytes;
+
+	if (argc < 4)
+		usage();
+
+	if (signal(SIGALRM, sigalrm) == SIG_ERR)
+		err("failed to arm SIGALRM");
+	alarm(ALARM_INTERVAL_SECS);
+
+	hpage_size = default_huge_page_size();
+	parse_test_type_arg(argv[1]);
+	bytes = atol(argv[2]) * 1024 * 1024;
+
+	if (test_collapse && bytes & (hpage_size - 1))
+		err("MiB must be multiple of %lu if :collapse mod set",
+		    hpage_size >> 20);
+
+	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+
+	if (test_collapse) {
+		/* nr_cpus must divide (bytes / page_size), otherwise,
+		 * area allocations of (nr_pages * paze_size) won't be a
+		 * multiple of hpage_size, even if bytes is a multiple of
+		 * hpage_size.
+		 *
+		 * This means that nr_cpus must divide (N * (2 << (H-P))
+		 * where:
+		 *	bytes = hpage_size * N
+		 *	hpage_size = 2 << H
+		 *	page_size = 2 << P
+		 *
+		 * And we want to chose nr_cpus to be the largest value
+		 * satisfying this constraint, not larger than the number
+		 * of online CPUs. Unfortunately, prime factorization of
+		 * N and nr_cpus may be arbitrary, so have to search for it.
+		 * Instead, just use the highest power of 2 dividing both
+		 * nr_cpus and (bytes / page_size).
+		 */
+		int x = factor_of_2(nr_cpus);
+		int y = factor_of_2(bytes / page_size);
+
+		nr_cpus = x < y ? x : y;
+	}
+	nr_pages_per_cpu = bytes / page_size / nr_cpus;
+	if (!nr_pages_per_cpu) {
+		_err("invalid MiB");
+		usage();
+	}
+
+	bounces = atoi(argv[3]);
+	if (bounces <= 0) {
+		_err("invalid bounces");
+		usage();
+	}
+	nr_pages = nr_pages_per_cpu * nr_cpus;
+
+	if (test_type == TEST_HUGETLB && map_shared) {
+		if (argc < 5)
+			usage();
+		huge_fd = open(argv[4], O_CREAT | O_RDWR, 0755);
+		if (huge_fd < 0)
+			err("Open of %s failed", argv[4]);
+		if (ftruncate(huge_fd, 0))
+			err("ftruncate %s to size 0 failed", argv[4]);
+	} else if (test_type == TEST_SHMEM) {
+		shm_fd = memfd_create(argv[0], 0);
+		if (shm_fd < 0)
+			err("memfd_create");
+		if (ftruncate(shm_fd, nr_pages * page_size * 2))
+			err("ftruncate");
+		if (fallocate(shm_fd,
+			      FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
+			      nr_pages * page_size * 2))
+			err("fallocate");
+	}
+	printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
+	       nr_pages, nr_pages_per_cpu);
+	return userfaultfd_stress();
+}
+
+#else /* __NR_userfaultfd */
+
+#warning "missing __NR_userfaultfd definition"
+
+int main(void)
+{
+	printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
+	return KSFT_SKIP;
+}
+
+#endif /* __NR_userfaultfd */