tools/testing/selftests/mm/uffd-stress.c - linux - Git at Google

 // 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).
  */

 #include "uffd-common.h"

 #ifdef __NR_userfaultfd

 #define BOUNCE_RANDOM		(1<<0)
 #define BOUNCE_RACINGFAULTS	(1<<1)
 #define BOUNCE_VERIFY		(1<<2)
 #define BOUNCE_POLL		(1<<3)
 static int bounces;

 /* exercise the test_uffdio_*_eexist every ALARM_INTERVAL_SECS */
 #define ALARM_INTERVAL_SECS 10
 static char *zeropage;
 pthread_attr_t attr;

 #define swap(a, b) \
 	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

 const char *examples =
 	"# Run anonymous memory test on 100MiB region with 99999 bounces:\n"
 	"./uffd-stress anon 100 99999\n\n"
 	"# Run share memory test on 1GiB region with 99 bounces:\n"
 	"./uffd-stress shmem 1000 99\n\n"
 	"# Run hugetlb memory test on 256MiB region with 50 bounces:\n"
 	"./uffd-stress hugetlb 256 50\n\n"
 	"# Run the same hugetlb test but using private file:\n"
 	"./uffd-stress hugetlb-private 256 50\n\n"
 	"# 10MiB-~6GiB 999 bounces anonymous test, "
 	"continue forever unless an error triggers\n"
 	"while ./uffd-stress anon $[RANDOM % 6000 + 10] 999; do true; done\n\n";

 static void usage(void)
 {
 	fprintf(stderr, "\nUsage: ./uffd-stress <test type> <MiB> <bounces>\n\n");
 	fprintf(stderr, "Supported <test type>: anon, hugetlb, "
 		"hugetlb-private, shmem, shmem-private\n\n");
 	fprintf(stderr, "Examples:\n\n");
 	fprintf(stderr, "%s", examples);
 	exit(1);
 }

 static void uffd_stats_reset(struct uffd_args *args, unsigned long n_cpus)
 {
 	int i;

 	for (i = 0; i < n_cpus; i++) {
 		args[i].cpu = i;
 		args[i].apply_wp = test_uffdio_wp;
 		args[i].missing_faults = 0;
 		args[i].wp_faults = 0;
 		args[i].minor_faults = 0;
 	}
 }

 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 int copy_page_retry(int ufd, unsigned long offset)
 {
 	return __copy_page(ufd, offset, true, test_uffdio_wp);
 }

 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;

 static void *uffd_read_thread(void *arg)
 {
 	struct uffd_args *args = (struct uffd_args *)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, args);
 	}

 	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_args *args)
 {
 	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, &args[cpu]))
 				err("uffd_poll_thread create");
 		} else {
 			if (pthread_create(&uffd_threads[cpu], &attr,
 					   uffd_read_thread,
 					   (void *)&args[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 *)&args[cpu]))
 				return 1;
 		} else {
 			if (pthread_cancel(uffd_threads[cpu]))
 				return 1;
 			if (pthread_join(uffd_threads[cpu], NULL))
 				return 1;
 		}
 	}

 	return 0;
 }

 static int userfaultfd_stress(void)
 {
 	void *area;
 	unsigned long nr;
 	struct uffd_args args[nr_cpus];
 	uint64_t mem_size = nr_pages * page_size;

 	memset(args, 0, sizeof(struct uffd_args) * nr_cpus);

 	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
 		err("context init failed");

 	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 */
 		if (uffd_register(uffd, area_dst, mem_size,
 				  true, test_uffdio_wp, false))
 			err("register failure");

 		if (area_dst_alias) {
 			if (uffd_register(uffd, area_dst_alias, mem_size,
 					  true, test_uffdio_wp, false))
 				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(args, nr_cpus);

 		/* bounce pass */
 		if (stress(args)) {
 			uffd_test_ctx_clear();
 			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 (uffd_unregister(uffd, area_dst, mem_size))
 			err("unregister failure");
 		if (area_dst_alias) {
 			if (uffd_unregister(uffd, area_dst_alias, mem_size))
 				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(args, nr_cpus);
 	}
 	uffd_test_ctx_clear();

 	return 0;
 }

 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;
 		map_shared = true;
 	} else if (!strcmp(type, "hugetlb-private")) {
 		test_type = TEST_HUGETLB;
 		uffd_test_ops = &hugetlb_uffd_test_ops;
 	} else if (!strcmp(type, "shmem")) {
 		map_shared = true;
 		test_type = TEST_SHMEM;
 		uffd_test_ops = &shmem_uffd_test_ops;
 	} else if (!strcmp(type, "shmem-private")) {
 		test_type = TEST_SHMEM;
 		uffd_test_ops = &shmem_uffd_test_ops;
 	}
 }

 static void parse_test_type_arg(const char *raw_type)
 {
 	uint64_t features = UFFD_API_FEATURES;

 	set_test_type(raw_type);

 	if (!test_type)
 		err("failed to parse test type argument: '%s'", raw_type);

 	if (test_type == TEST_HUGETLB)
 		page_size = default_huge_page_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.
 	 */

 	if (userfaultfd_open(&features))
 		err("Userfaultfd open failed");

 	test_uffdio_wp = test_uffdio_wp &&
 		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);

 	close(uffd);
 	uffd = -1;
 }

 static void sigalrm(int sig)
 {
 	if (sig != SIGALRM)
 		abort();
 	test_uffdio_copy_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);

 	parse_test_type_arg(argv[1]);
 	bytes = atol(argv[2]) * 1024 * 1024;

 	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);

 	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;

 	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 */
	// 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).
	*/

	#include "uffd-common.h"

	#ifdef __NR_userfaultfd

	#define BOUNCE_RANDOM (1<<0)
	#define BOUNCE_RACINGFAULTS (1<<1)
	#define BOUNCE_VERIFY (1<<2)
	#define BOUNCE_POLL (1<<3)
	static int bounces;

	/* exercise the test_uffdio__eexist every ALARM_INTERVAL_SECS /
	#define ALARM_INTERVAL_SECS 10
	static char *zeropage;
	pthread_attr_t attr;

	#define swap(a, b) \
	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

	const char *examples =
	"# Run anonymous memory test on 100MiB region with 99999 bounces:\n"
	"./uffd-stress anon 100 99999\n\n"
	"# Run share memory test on 1GiB region with 99 bounces:\n"
	"./uffd-stress shmem 1000 99\n\n"
	"# Run hugetlb memory test on 256MiB region with 50 bounces:\n"
	"./uffd-stress hugetlb 256 50\n\n"
	"# Run the same hugetlb test but using private file:\n"
	"./uffd-stress hugetlb-private 256 50\n\n"
	"# 10MiB-~6GiB 999 bounces anonymous test, "
	"continue forever unless an error triggers\n"
	"while ./uffd-stress anon $[RANDOM % 6000 + 10] 999; do true; done\n\n";

	static void usage(void)
	{
	fprintf(stderr, "\nUsage: ./uffd-stress <test type> <MiB> <bounces>\n\n");
	fprintf(stderr, "Supported <test type>: anon, hugetlb, "
	"hugetlb-private, shmem, shmem-private\n\n");
	fprintf(stderr, "Examples:\n\n");
	fprintf(stderr, "%s", examples);
	exit(1);
	}

	static void uffd_stats_reset(struct uffd_args *args, unsigned long n_cpus)
	{
	int i;

	for (i = 0; i < n_cpus; i++) {
	args[i].cpu = i;
	args[i].apply_wp = test_uffdio_wp;
	args[i].missing_faults = 0;
	args[i].wp_faults = 0;
	args[i].minor_faults = 0;
	}
	}

	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 int copy_page_retry(int ufd, unsigned long offset)
	{
	return __copy_page(ufd, offset, true, test_uffdio_wp);
	}

	pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;

	static void uffd_read_thread(void arg)
	{
	struct uffd_args args = (struct uffd_args )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, args);
	}

	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_args *args)
	{
	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, &args[cpu]))
	err("uffd_poll_thread create");
	} else {
	if (pthread_create(&uffd_threads[cpu], &attr,
	uffd_read_thread,
	(void *)&args[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 *)&args[cpu]))
	return 1;
	} else {
	if (pthread_cancel(uffd_threads[cpu]))
	return 1;
	if (pthread_join(uffd_threads[cpu], NULL))
	return 1;
	}
	}

	return 0;
	}

	static int userfaultfd_stress(void)
	{
	void *area;
	unsigned long nr;
	struct uffd_args args[nr_cpus];
	uint64_t mem_size = nr_pages * page_size;

	memset(args, 0, sizeof(struct uffd_args) * nr_cpus);

	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
	err("context init failed");

	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, 1610241024);

	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 */
	if (uffd_register(uffd, area_dst, mem_size,
	true, test_uffdio_wp, false))
	err("register failure");

	if (area_dst_alias) {
	if (uffd_register(uffd, area_dst_alias, mem_size,
	true, test_uffdio_wp, false))
	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(args, nr_cpus);

	/* bounce pass */
	if (stress(args)) {
	uffd_test_ctx_clear();
	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 (uffd_unregister(uffd, area_dst, mem_size))
	err("unregister failure");
	if (area_dst_alias) {
	if (uffd_unregister(uffd, area_dst_alias, mem_size))
	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(args, nr_cpus);
	}
	uffd_test_ctx_clear();

	return 0;
	}

	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;
	map_shared = true;
	} else if (!strcmp(type, "hugetlb-private")) {
	test_type = TEST_HUGETLB;
	uffd_test_ops = &hugetlb_uffd_test_ops;
	} else if (!strcmp(type, "shmem")) {
	map_shared = true;
	test_type = TEST_SHMEM;
	uffd_test_ops = &shmem_uffd_test_ops;
	} else if (!strcmp(type, "shmem-private")) {
	test_type = TEST_SHMEM;
	uffd_test_ops = &shmem_uffd_test_ops;
	}
	}

	static void parse_test_type_arg(const char *raw_type)
	{
	uint64_t features = UFFD_API_FEATURES;

	set_test_type(raw_type);

	if (!test_type)
	err("failed to parse test type argument: '%s'", raw_type);

	if (test_type == TEST_HUGETLB)
	page_size = default_huge_page_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.
	*/

	if (userfaultfd_open(&features))
	err("Userfaultfd open failed");

	test_uffdio_wp = test_uffdio_wp &&
	(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);

	close(uffd);
	uffd = -1;
	}

	static void sigalrm(int sig)
	{
	if (sig != SIGALRM)
	abort();
	test_uffdio_copy_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);

	parse_test_type_arg(argv[1]);
	bytes = atol(argv[2]) * 1024 * 1024;

	nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);

	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;

	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 */