1 files changed, 745 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
new file mode 100644
index 000000000000..edd02328f77b
--- /dev/null
+++ b/tools/testing/selftests/mm/uffd-common.c
@@ -0,0 +1,745 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Userfaultfd tests util functions
+ *
+ * Copyright (C) 2015-2023  Red Hat, Inc.
+ */
+
+#include "uffd-common.h"
+
+uffd_test_ops_t *uffd_test_ops;
+uffd_test_case_ops_t *uffd_test_case_ops;
+
+
+/* pthread_mutex_t starts at page offset 0 */
+pthread_mutex_t *area_mutex(char *area, unsigned long nr, uffd_global_test_opts_t *gopts)
+{
+	return (pthread_mutex_t *) (area + nr * gopts->page_size);
+}
+
+/*
+ * count is placed in the page after pthread_mutex_t naturally aligned
+ * to avoid non alignment faults on non-x86 archs.
+ */
+volatile unsigned long long *area_count(char *area, unsigned long nr,
+					uffd_global_test_opts_t *gopts)
+{
+	return (volatile unsigned long long *)
+	       ((unsigned long)(area + nr * gopts->page_size +
+	       sizeof(pthread_mutex_t) + sizeof(unsigned long long) - 1) &
+	       ~(unsigned long)(sizeof(unsigned long long) - 1));
+}
+
+static int uffd_mem_fd_create(off_t mem_size, bool hugetlb)
+{
+	unsigned int memfd_flags = 0;
+	int mem_fd;
+
+	if (hugetlb)
+		memfd_flags = MFD_HUGETLB;
+	mem_fd = memfd_create("uffd-test", memfd_flags);
+	if (mem_fd < 0)
+		err("memfd_create");
+	if (ftruncate(mem_fd, mem_size))
+		err("ftruncate");
+	if (fallocate(mem_fd,
+		      FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
+		      mem_size))
+		err("fallocate");
+
+	return mem_fd;
+}
+
+static void anon_release_pages(uffd_global_test_opts_t *gopts, char *rel_area)
+{
+	if (madvise(rel_area, gopts->nr_pages * gopts->page_size, MADV_DONTNEED))
+		err("madvise(MADV_DONTNEED) failed");
+}
+
+static int anon_allocate_area(uffd_global_test_opts_t *gopts, void **alloc_area, bool is_src)
+{
+	*alloc_area = mmap(NULL, gopts->nr_pages * gopts->page_size, PROT_READ | PROT_WRITE,
+			   MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (*alloc_area == MAP_FAILED) {
+		*alloc_area = NULL;
+		return -errno;
+	}
+	return 0;
+}
+
+static void noop_alias_mapping(uffd_global_test_opts_t *gopts, __u64 *start,
+			       size_t len, unsigned long offset)
+{
+}
+
+static void hugetlb_release_pages(uffd_global_test_opts_t *gopts, char *rel_area)
+{
+	if (!gopts->map_shared) {
+		if (madvise(rel_area, gopts->nr_pages * gopts->page_size, MADV_DONTNEED))
+			err("madvise(MADV_DONTNEED) failed");
+	} else {
+		if (madvise(rel_area, gopts->nr_pages * gopts->page_size, MADV_REMOVE))
+			err("madvise(MADV_REMOVE) failed");
+	}
+}
+
+static int hugetlb_allocate_area(uffd_global_test_opts_t *gopts, void **alloc_area, bool is_src)
+{
+	off_t size = gopts->nr_pages * gopts->page_size;
+	off_t offset = is_src ? 0 : size;
+	void *area_alias = NULL;
+	char **alloc_area_alias;
+	int mem_fd = uffd_mem_fd_create(size * 2, true);
+
+	*alloc_area = mmap(NULL, size, PROT_READ | PROT_WRITE,
+			   (gopts->map_shared ? MAP_SHARED : MAP_PRIVATE) |
+			   (is_src ? 0 : MAP_NORESERVE),
+			   mem_fd, offset);
+	if (*alloc_area == MAP_FAILED) {
+		*alloc_area = NULL;
+		return -errno;
+	}
+
+	if (gopts->map_shared) {
+		area_alias = mmap(NULL, size, PROT_READ | PROT_WRITE,
+				  MAP_SHARED, mem_fd, offset);
+		if (area_alias == MAP_FAILED)
+			return -errno;
+	}
+
+	if (is_src) {
+		alloc_area_alias = &gopts->area_src_alias;
+	} else {
+		alloc_area_alias = &gopts->area_dst_alias;
+	}
+	if (area_alias)
+		*alloc_area_alias = area_alias;
+
+	close(mem_fd);
+	return 0;
+}
+
+static void hugetlb_alias_mapping(uffd_global_test_opts_t *gopts, __u64 *start,
+				  size_t len, unsigned long offset)
+{
+	if (!gopts->map_shared)
+		return;
+
+	*start = (unsigned long) gopts->area_dst_alias + offset;
+}
+
+static void shmem_release_pages(uffd_global_test_opts_t *gopts, char *rel_area)
+{
+	if (madvise(rel_area, gopts->nr_pages * gopts->page_size, MADV_REMOVE))
+		err("madvise(MADV_REMOVE) failed");
+}
+
+static int shmem_allocate_area(uffd_global_test_opts_t *gopts, void **alloc_area, bool is_src)
+{
+	void *area_alias = NULL;
+	size_t bytes = gopts->nr_pages * gopts->page_size, hpage_size = read_pmd_pagesize();
+	unsigned long offset = is_src ? 0 : bytes;
+	char *p = NULL, *p_alias = NULL;
+	int mem_fd = uffd_mem_fd_create(bytes * 2, false);
+	size_t region_size = bytes * 2 + hpage_size;
+
+	void *reserve = mmap(NULL, region_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS,
+			-1, 0);
+	if (reserve == MAP_FAILED) {
+		close(mem_fd);
+		return -errno;
+	}
+
+	p = reserve;
+	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_FIXED | MAP_SHARED,
+			   mem_fd, offset);
+	if (*alloc_area == MAP_FAILED) {
+		*alloc_area = NULL;
+		munmap(reserve, region_size);
+		close(mem_fd);
+		return -errno;
+	}
+	if (*alloc_area != p)
+		err("mmap of memfd failed at %p", p);
+
+	area_alias = mmap(p_alias, bytes, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED,
+			  mem_fd, offset);
+	if (area_alias == MAP_FAILED) {
+		*alloc_area = NULL;
+		munmap(reserve, region_size);
+		close(mem_fd);
+		return -errno;
+	}
+	if (area_alias != p_alias)
+		err("mmap of anonymous memory failed at %p", p_alias);
+
+	if (is_src)
+		gopts->area_src_alias = area_alias;
+	else
+		gopts->area_dst_alias = area_alias;
+
+	close(mem_fd);
+	return 0;
+}
+
+static void shmem_alias_mapping(uffd_global_test_opts_t *gopts, __u64 *start,
+				size_t len, unsigned long offset)
+{
+	*start = (unsigned long)gopts->area_dst_alias + offset;
+}
+
+static void shmem_check_pmd_mapping(uffd_global_test_opts_t *gopts, void *p, int expect_nr_hpages)
+{
+	if (!check_huge_shmem(gopts->area_dst_alias, expect_nr_hpages,
+			      read_pmd_pagesize()))
+		err("Did not find expected %d number of hugepages",
+		    expect_nr_hpages);
+}
+
+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,
+};
+
+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,
+};
+
+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,
+};
+
+void uffd_stats_report(struct uffd_args *args, 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 += args[i].missing_faults;
+		wp_total += args[i].wp_faults;
+		minor_total += args[i].minor_faults;
+	}
+
+	printf("userfaults: ");
+	if (miss_total) {
+		printf("%llu missing (", miss_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", args[i].missing_faults);
+		printf("\b) ");
+	}
+	if (wp_total) {
+		printf("%llu wp (", wp_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", args[i].wp_faults);
+		printf("\b) ");
+	}
+	if (minor_total) {
+		printf("%llu minor (", minor_total);
+		for (i = 0; i < n_cpus; i++)
+			printf("%lu+", args[i].minor_faults);
+		printf("\b)");
+	}
+	printf("\n");
+}
+
+int userfaultfd_open(uffd_global_test_opts_t *gopts, uint64_t *features)
+{
+	struct uffdio_api uffdio_api;
+
+	gopts->uffd = uffd_open(UFFD_FLAGS);
+	if (gopts->uffd < 0)
+		return -1;
+	gopts->uffd_flags = fcntl(gopts->uffd, F_GETFD, NULL);
+
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = *features;
+	if (ioctl(gopts->uffd, UFFDIO_API, &uffdio_api))
+		/* Probably lack of CAP_PTRACE? */
+		return -1;
+	if (uffdio_api.api != UFFD_API)
+		err("UFFDIO_API error: %" PRIu64, (uint64_t)uffdio_api.api);
+
+	*features = uffdio_api.features;
+	return 0;
+}
+
+static inline void munmap_area(uffd_global_test_opts_t *gopts, void **area)
+{
+	if (*area)
+		if (munmap(*area, gopts->nr_pages * gopts->page_size))
+			err("munmap");
+
+	*area = NULL;
+}
+
+void uffd_test_ctx_clear(uffd_global_test_opts_t *gopts)
+{
+	size_t i;
+
+	if (gopts->pipefd) {
+		for (i = 0; i < gopts->nr_parallel * 2; ++i) {
+			if (close(gopts->pipefd[i]))
+				err("close pipefd");
+		}
+		free(gopts->pipefd);
+		gopts->pipefd = NULL;
+	}
+
+	if (gopts->count_verify) {
+		free(gopts->count_verify);
+		gopts->count_verify = NULL;
+	}
+
+	if (gopts->uffd != -1) {
+		if (close(gopts->uffd))
+			err("close uffd");
+		gopts->uffd = -1;
+	}
+
+	munmap_area(gopts, (void **)&gopts->area_src);
+	munmap_area(gopts, (void **)&gopts->area_src_alias);
+	munmap_area(gopts, (void **)&gopts->area_dst);
+	munmap_area(gopts, (void **)&gopts->area_dst_alias);
+	munmap_area(gopts, (void **)&gopts->area_remap);
+}
+
+int uffd_test_ctx_init(uffd_global_test_opts_t *gopts, uint64_t features, const char **errmsg)
+{
+	unsigned long nr, cpu;
+	int ret;
+
+	gopts->area_src_alias = NULL;
+	gopts->area_dst_alias = NULL;
+	gopts->area_remap = NULL;
+
+	if (uffd_test_case_ops && uffd_test_case_ops->pre_alloc) {
+		ret = uffd_test_case_ops->pre_alloc(gopts, errmsg);
+		if (ret)
+			return ret;
+	}
+
+	ret = uffd_test_ops->allocate_area(gopts, (void **) &gopts->area_src, true);
+	ret |= uffd_test_ops->allocate_area(gopts, (void **) &gopts->area_dst, false);
+	if (ret) {
+		if (errmsg)
+			*errmsg = "memory allocation failed";
+		return ret;
+	}
+
+	if (uffd_test_case_ops && uffd_test_case_ops->post_alloc) {
+		ret = uffd_test_case_ops->post_alloc(gopts, errmsg);
+		if (ret)
+			return ret;
+	}
+
+	ret = userfaultfd_open(gopts, &features);
+	if (ret) {
+		if (errmsg)
+			*errmsg = "possible lack of privilege";
+		return ret;
+	}
+
+	gopts->count_verify = malloc(gopts->nr_pages * sizeof(unsigned long long));
+	if (!gopts->count_verify)
+		err("count_verify");
+
+	for (nr = 0; nr < gopts->nr_pages; nr++) {
+		*area_mutex(gopts->area_src, nr, gopts) =
+			(pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER;
+		gopts->count_verify[nr] = *area_count(gopts->area_src, nr, gopts) = 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(gopts->area_src, nr, gopts) + 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 erroneously 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(gopts, gopts->area_dst);
+
+	gopts->pipefd = malloc(sizeof(int) * gopts->nr_parallel * 2);
+	if (!gopts->pipefd)
+		err("pipefd");
+	for (cpu = 0; cpu < gopts->nr_parallel; cpu++)
+		if (pipe2(&gopts->pipefd[cpu * 2], O_CLOEXEC | O_NONBLOCK))
+			err("pipe");
+
+	return 0;
+}
+
+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, bool wp)
+{
+	struct uffdio_continue req;
+	int ret;
+
+	req.range.start = start;
+	req.range.len = len;
+	req.mode = 0;
+	if (wp)
+		req.mode |= UFFDIO_CONTINUE_MODE_WP;
+
+	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);
+}
+
+int uffd_read_msg(uffd_global_test_opts_t *gopts, struct uffd_msg *msg)
+{
+	int ret = read(gopts->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;
+}
+
+void uffd_handle_page_fault(uffd_global_test_opts_t *gopts, struct uffd_msg *msg,
+			    struct uffd_args *args)
+{
+	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(gopts->uffd, msg->arg.pagefault.address, gopts->page_size, false);
+		args->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 *)(gopts->area_dst +
+		       ((char *)msg->arg.pagefault.address -
+		       gopts->area_dst_alias));
+		for (b = 0; b < gopts->page_size; ++b)
+			area[b] = ~area[b];
+		continue_range(gopts->uffd, msg->arg.pagefault.address, gopts->page_size,
+			       args->apply_wp);
+		args->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 - gopts->area_dst;
+		offset &= ~(gopts->page_size-1);
+
+		if (copy_page(gopts, offset, args->apply_wp))
+			args->missing_faults++;
+	}
+}
+
+void *uffd_poll_thread(void *arg)
+{
+	struct uffd_args *args = (struct uffd_args *)arg;
+	uffd_global_test_opts_t *gopts = args->gopts;
+	unsigned long cpu = args->cpu;
+	struct pollfd pollfd[2];
+	struct uffd_msg msg;
+	struct uffdio_register uffd_reg;
+	int ret;
+	char tmp_chr;
+
+	if (!args->handle_fault)
+		args->handle_fault = uffd_handle_page_fault;
+
+	pollfd[0].fd = gopts->uffd;
+	pollfd[0].events = POLLIN;
+	pollfd[1].fd = gopts->pipefd[cpu*2];
+	pollfd[1].events = POLLIN;
+
+	gopts->ready_for_fork = true;
+
+	for (;;) {
+		ret = poll(pollfd, 2, -1);
+		if (ret <= 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
+			err("poll error: %d", ret);
+		}
+		if (pollfd[1].revents) {
+			if (!(pollfd[1].revents & POLLIN))
+				err("pollfd[1].revents %d", pollfd[1].revents);
+			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(gopts, &msg))
+			continue;
+		switch (msg.event) {
+		default:
+			err("unexpected msg event %u\n", msg.event);
+			break;
+		case UFFD_EVENT_PAGEFAULT:
+			args->handle_fault(gopts, &msg, args);
+			break;
+		case UFFD_EVENT_FORK:
+			close(gopts->uffd);
+			gopts->uffd = msg.arg.fork.ufd;
+			pollfd[0].fd = gopts->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(gopts->uffd, UFFDIO_UNREGISTER, &uffd_reg.range))
+				err("remove failure");
+			break;
+		case UFFD_EVENT_REMAP:
+			gopts->area_remap = gopts->area_dst;  /* save for later unmap */
+			gopts->area_dst = (char *)(unsigned long)msg.arg.remap.to;
+			break;
+		}
+	}
+
+	return NULL;
+}
+
+static void retry_copy_page(uffd_global_test_opts_t *gopts, struct uffdio_copy *uffdio_copy,
+			    unsigned long offset)
+{
+	uffd_test_ops->alias_mapping(gopts,
+				     &uffdio_copy->dst,
+				     uffdio_copy->len,
+				     offset);
+	if (ioctl(gopts->uffd, 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);
+}
+
+int __copy_page(uffd_global_test_opts_t *gopts, unsigned long offset, bool retry, bool wp)
+{
+	struct uffdio_copy uffdio_copy;
+
+	if (offset >= gopts->nr_pages * gopts->page_size)
+		err("unexpected offset %lu\n", offset);
+	uffdio_copy.dst = (unsigned long) gopts->area_dst + offset;
+	uffdio_copy.src = (unsigned long) gopts->area_src + offset;
+	uffdio_copy.len = gopts->page_size;
+	if (wp)
+		uffdio_copy.mode = UFFDIO_COPY_MODE_WP;
+	else
+		uffdio_copy.mode = 0;
+	uffdio_copy.copy = 0;
+	if (ioctl(gopts->uffd, 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(gopts->uffd, uffdio_copy.dst, gopts->page_size);
+	} else if (uffdio_copy.copy != gopts->page_size) {
+		err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy);
+	} else {
+		if (gopts->test_uffdio_copy_eexist && retry) {
+			gopts->test_uffdio_copy_eexist = false;
+			retry_copy_page(gopts, &uffdio_copy, offset);
+		}
+		return 1;
+	}
+	return 0;
+}
+
+int copy_page(uffd_global_test_opts_t *gopts, unsigned long offset, bool wp)
+{
+	return __copy_page(gopts, offset, false, wp);
+}
+
+int move_page(uffd_global_test_opts_t *gopts, unsigned long offset, unsigned long len)
+{
+	struct uffdio_move uffdio_move;
+
+	if (offset + len > gopts->nr_pages * gopts->page_size)
+		err("unexpected offset %lu and length %lu\n", offset, len);
+	uffdio_move.dst = (unsigned long) gopts->area_dst + offset;
+	uffdio_move.src = (unsigned long) gopts->area_src + offset;
+	uffdio_move.len = len;
+	uffdio_move.mode = UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
+	uffdio_move.move = 0;
+	if (ioctl(gopts->uffd, UFFDIO_MOVE, &uffdio_move)) {
+		/* real retval in uffdio_move.move */
+		if (uffdio_move.move != -EEXIST)
+			err("UFFDIO_MOVE error: %"PRId64,
+			    (int64_t)uffdio_move.move);
+		wake_range(gopts->uffd, uffdio_move.dst, len);
+	} else if (uffdio_move.move != len) {
+		err("UFFDIO_MOVE error: %"PRId64, (int64_t)uffdio_move.move);
+	} else
+		return 1;
+	return 0;
+}
+
+int uffd_open_dev(unsigned int flags)
+{
+	int fd, uffd;
+
+	fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+	uffd = ioctl(fd, USERFAULTFD_IOC_NEW, flags);
+	close(fd);
+
+	return uffd;
+}
+
+int uffd_open_sys(unsigned int flags)
+{
+#ifdef __NR_userfaultfd
+	return syscall(__NR_userfaultfd, flags);
+#else
+	return -1;
+#endif
+}
+
+int uffd_open(unsigned int flags)
+{
+	int uffd = uffd_open_sys(flags);
+
+	if (uffd < 0)
+		uffd = uffd_open_dev(flags);
+
+	return uffd;
+}
+
+int uffd_get_features(uint64_t *features)
+{
+	struct uffdio_api uffdio_api = { .api = UFFD_API, .features = 0 };
+	/*
+	 * This should by default work in most kernels; the feature list
+	 * will be the same no matter what we pass in here.
+	 */
+	int fd = uffd_open(UFFD_USER_MODE_ONLY);
+
+	if (fd < 0)
+		/* Maybe the kernel is older than user-only mode? */
+		fd = uffd_open(0);
+
+	if (fd < 0)
+		return fd;
+
+	if (ioctl(fd, UFFDIO_API, &uffdio_api)) {
+		close(fd);
+		return -errno;
+	}
+
+	*features = uffdio_api.features;
+	close(fd);
+
+	return 0;
+}