2 * Stress userfaultfd syscall.
4 * Copyright (C) 2015 Red Hat, Inc.
6 * This work is licensed under the terms of the GNU GPL, version 2. See
7 * the COPYING file in the top-level directory.
9 * This test allocates two virtual areas and bounces the physical
10 * memory across the two virtual areas (from area_src to area_dst)
13 * There are three threads running per CPU:
15 * 1) one per-CPU thread takes a per-page pthread_mutex in a random
16 * page of the area_dst (while the physical page may still be in
17 * area_src), and increments a per-page counter in the same page,
18 * and checks its value against a verification region.
20 * 2) another per-CPU thread handles the userfaults generated by
21 * thread 1 above. userfaultfd blocking reads or poll() modes are
22 * exercised interleaved.
24 * 3) one last per-CPU thread transfers the memory in the background
25 * at maximum bandwidth (if not already transferred by thread
26 * 2). Each cpu thread takes cares of transferring a portion of the
29 * When all threads of type 3 completed the transfer, one bounce is
30 * complete. area_src and area_dst are then swapped. All threads are
31 * respawned and so the bounce is immediately restarted in the
34 * per-CPU threads 1 by triggering userfaults inside
35 * pthread_mutex_lock will also verify the atomicity of the memory
36 * transfer (UFFDIO_COPY).
38 * The program takes two parameters: the amounts of physical memory in
39 * megabytes (MiB) of the area and the number of bounces to execute.
41 * # 100MiB 99999 bounces
42 * ./userfaultfd 100 99999
45 * ./userfaultfd 1000 99
47 * # 10MiB-~6GiB 999 bounces, continue forever unless an error triggers
48 * while ./userfaultfd $[RANDOM % 6000 + 10] 999; do true; done
56 #include <sys/types.h>
63 #include <linux/mman.h>
65 #include <sys/syscall.h>
66 #include <sys/ioctl.h>
68 #include <linux/userfaultfd.h>
70 #ifdef __NR_userfaultfd
72 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
74 #define BOUNCE_RANDOM (1<<0)
75 #define BOUNCE_RACINGFAULTS (1<<1)
76 #define BOUNCE_VERIFY (1<<2)
77 #define BOUNCE_POLL (1<<3)
80 static unsigned long long *count_verify;
81 static int uffd, finished, *pipefd;
82 static char *area_src, *area_dst;
83 static char *zeropage;
86 /* pthread_mutex_t starts at page offset 0 */
87 #define area_mutex(___area, ___nr) \
88 ((pthread_mutex_t *) ((___area) + (___nr)*page_size))
90 * count is placed in the page after pthread_mutex_t naturally aligned
91 * to avoid non alignment faults on non-x86 archs.
93 #define area_count(___area, ___nr) \
94 ((volatile unsigned long long *) ((unsigned long) \
95 ((___area) + (___nr)*page_size + \
96 sizeof(pthread_mutex_t) + \
97 sizeof(unsigned long long) - 1) & \
98 ~(unsigned long)(sizeof(unsigned long long) \
101 static int my_bcmp(char *str1, char *str2, size_t n)
104 for (i = 0; i < n; i++)
105 if (str1[i] != str2[i])
110 static void *locking_thread(void *arg)
112 unsigned long cpu = (unsigned long) arg;
113 struct random_data rand;
114 unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
116 unsigned long long count;
121 if (bounces & BOUNCE_RANDOM) {
122 seed = (unsigned int) time(NULL) - bounces;
123 if (!(bounces & BOUNCE_RACINGFAULTS))
125 bzero(&rand, sizeof(rand));
126 bzero(&randstate, sizeof(randstate));
127 if (initstate_r(seed, randstate, sizeof(randstate), &rand))
128 fprintf(stderr, "srandom_r error\n"), exit(1);
131 if (!(bounces & BOUNCE_RACINGFAULTS))
132 page_nr += cpu * nr_pages_per_cpu;
136 if (bounces & BOUNCE_RANDOM) {
137 if (random_r(&rand, &rand_nr))
138 fprintf(stderr, "random_r 1 error\n"), exit(1);
140 if (sizeof(page_nr) > sizeof(rand_nr)) {
141 if (random_r(&rand, &rand_nr))
142 fprintf(stderr, "random_r 2 error\n"), exit(1);
143 page_nr |= (((unsigned long) rand_nr) << 16) <<
151 if (bounces & BOUNCE_VERIFY) {
152 count = *area_count(area_dst, page_nr);
155 "page_nr %lu wrong count %Lu %Lu\n",
157 count_verify[page_nr]), exit(1);
161 * We can't use bcmp (or memcmp) because that
162 * returns 0 erroneously if the memory is
163 * changing under it (even if the end of the
164 * page is never changing and always
168 if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
171 "my_bcmp page_nr %lu wrong count %Lu %Lu\n",
173 count_verify[page_nr]), exit(1);
178 /* uncomment the below line to test with mutex */
179 /* pthread_mutex_lock(area_mutex(area_dst, page_nr)); */
180 while (!bcmp(area_dst + page_nr * page_size, zeropage,
186 /* uncomment below line to test with mutex */
187 /* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
190 "page_nr %lu all zero thread %lu %p %lu\n",
191 page_nr, cpu, area_dst + page_nr * page_size,
199 pthread_mutex_lock(area_mutex(area_dst, page_nr));
200 count = *area_count(area_dst, page_nr);
201 if (count != count_verify[page_nr]) {
203 "page_nr %lu memory corruption %Lu %Lu\n",
205 count_verify[page_nr]), exit(1);
208 *area_count(area_dst, page_nr) = count_verify[page_nr] = count;
209 pthread_mutex_unlock(area_mutex(area_dst, page_nr));
211 if (time(NULL) - start > 1)
213 "userfault too slow %ld "
214 "possible false positive with overcommit\n",
221 static int copy_page(unsigned long offset)
223 struct uffdio_copy uffdio_copy;
225 if (offset >= nr_pages * page_size)
226 fprintf(stderr, "unexpected offset %lu\n",
228 uffdio_copy.dst = (unsigned long) area_dst + offset;
229 uffdio_copy.src = (unsigned long) area_src + offset;
230 uffdio_copy.len = page_size;
231 uffdio_copy.mode = 0;
232 uffdio_copy.copy = 0;
233 if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy)) {
234 /* real retval in ufdio_copy.copy */
235 if (uffdio_copy.copy != -EEXIST)
236 fprintf(stderr, "UFFDIO_COPY error %Ld\n",
237 uffdio_copy.copy), exit(1);
238 } else if (uffdio_copy.copy != page_size) {
239 fprintf(stderr, "UFFDIO_COPY unexpected copy %Ld\n",
240 uffdio_copy.copy), exit(1);
246 static void *uffd_poll_thread(void *arg)
248 unsigned long cpu = (unsigned long) arg;
249 struct pollfd pollfd[2];
252 unsigned long offset;
254 unsigned long userfaults = 0;
257 pollfd[0].events = POLLIN;
258 pollfd[1].fd = pipefd[cpu*2];
259 pollfd[1].events = POLLIN;
262 ret = poll(pollfd, 2, -1);
264 fprintf(stderr, "poll error %d\n", ret), exit(1);
266 perror("poll"), exit(1);
267 if (pollfd[1].revents & POLLIN) {
268 if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
269 fprintf(stderr, "read pipefd error\n"),
273 if (!(pollfd[0].revents & POLLIN))
274 fprintf(stderr, "pollfd[0].revents %d\n",
275 pollfd[0].revents), exit(1);
276 ret = read(uffd, &msg, sizeof(msg));
280 perror("nonblocking read error"), exit(1);
282 if (msg.event != UFFD_EVENT_PAGEFAULT)
283 fprintf(stderr, "unexpected msg event %u\n",
285 if (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
286 fprintf(stderr, "unexpected write fault\n"), exit(1);
287 offset = (char *)(unsigned long)msg.arg.pagefault.address -
289 offset &= ~(page_size-1);
290 if (copy_page(offset))
293 return (void *)userfaults;
296 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
298 static void *uffd_read_thread(void *arg)
300 unsigned long *this_cpu_userfaults;
302 unsigned long offset;
305 this_cpu_userfaults = (unsigned long *) arg;
306 *this_cpu_userfaults = 0;
308 pthread_mutex_unlock(&uffd_read_mutex);
309 /* from here cancellation is ok */
312 ret = read(uffd, &msg, sizeof(msg));
313 if (ret != sizeof(msg)) {
315 perror("blocking read error"), exit(1);
317 fprintf(stderr, "short read\n"), exit(1);
319 if (msg.event != UFFD_EVENT_PAGEFAULT)
320 fprintf(stderr, "unexpected msg event %u\n",
322 if (bounces & BOUNCE_VERIFY &&
323 msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
324 fprintf(stderr, "unexpected write fault\n"), exit(1);
325 offset = (char *)(unsigned long)msg.arg.pagefault.address -
327 offset &= ~(page_size-1);
328 if (copy_page(offset))
329 (*this_cpu_userfaults)++;
334 static void *background_thread(void *arg)
336 unsigned long cpu = (unsigned long) arg;
337 unsigned long page_nr;
339 for (page_nr = cpu * nr_pages_per_cpu;
340 page_nr < (cpu+1) * nr_pages_per_cpu;
342 copy_page(page_nr * page_size);
347 static int stress(unsigned long *userfaults)
350 pthread_t locking_threads[nr_cpus];
351 pthread_t uffd_threads[nr_cpus];
352 pthread_t background_threads[nr_cpus];
353 void **_userfaults = (void **) userfaults;
356 for (cpu = 0; cpu < nr_cpus; cpu++) {
357 if (pthread_create(&locking_threads[cpu], &attr,
358 locking_thread, (void *)cpu))
360 if (bounces & BOUNCE_POLL) {
361 if (pthread_create(&uffd_threads[cpu], &attr,
362 uffd_poll_thread, (void *)cpu))
365 if (pthread_create(&uffd_threads[cpu], &attr,
369 pthread_mutex_lock(&uffd_read_mutex);
371 if (pthread_create(&background_threads[cpu], &attr,
372 background_thread, (void *)cpu))
375 for (cpu = 0; cpu < nr_cpus; cpu++)
376 if (pthread_join(background_threads[cpu], NULL))
380 * Be strict and immediately zap area_src, the whole area has
381 * been transferred already by the background treads. The
382 * area_src could then be faulted in in a racy way by still
383 * running uffdio_threads reading zeropages after we zapped
384 * area_src (but they're guaranteed to get -EEXIST from
385 * UFFDIO_COPY without writing zero pages into area_dst
386 * because the background threads already completed).
388 if (madvise(area_src, nr_pages * page_size, MADV_DONTNEED)) {
393 for (cpu = 0; cpu < nr_cpus; cpu++) {
395 if (bounces & BOUNCE_POLL) {
396 if (write(pipefd[cpu*2+1], &c, 1) != 1) {
397 fprintf(stderr, "pipefd write error\n");
400 if (pthread_join(uffd_threads[cpu], &_userfaults[cpu]))
403 if (pthread_cancel(uffd_threads[cpu]))
405 if (pthread_join(uffd_threads[cpu], NULL))
411 for (cpu = 0; cpu < nr_cpus; cpu++)
412 if (pthread_join(locking_threads[cpu], NULL))
418 static int userfaultfd_stress(void)
423 struct uffdio_register uffdio_register;
424 struct uffdio_api uffdio_api;
427 unsigned long userfaults[nr_cpus];
429 if (posix_memalign(&area, page_size, nr_pages * page_size)) {
430 fprintf(stderr, "out of memory\n");
434 if (posix_memalign(&area, page_size, nr_pages * page_size)) {
435 fprintf(stderr, "out of memory\n");
440 uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
443 "userfaultfd syscall not available in this kernel\n");
446 uffd_flags = fcntl(uffd, F_GETFD, NULL);
448 uffdio_api.api = UFFD_API;
449 uffdio_api.features = 0;
450 if (ioctl(uffd, UFFDIO_API, &uffdio_api)) {
451 fprintf(stderr, "UFFDIO_API\n");
454 if (uffdio_api.api != UFFD_API) {
455 fprintf(stderr, "UFFDIO_API error %Lu\n", uffdio_api.api);
459 count_verify = malloc(nr_pages * sizeof(unsigned long long));
461 perror("count_verify");
465 for (nr = 0; nr < nr_pages; nr++) {
466 *area_mutex(area_src, nr) = (pthread_mutex_t)
467 PTHREAD_MUTEX_INITIALIZER;
468 count_verify[nr] = *area_count(area_src, nr) = 1;
470 * In the transition between 255 to 256, powerpc will
471 * read out of order in my_bcmp and see both bytes as
472 * zero, so leave a placeholder below always non-zero
473 * after the count, to avoid my_bcmp to trigger false
476 *(area_count(area_src, nr) + 1) = 1;
479 pipefd = malloc(sizeof(int) * nr_cpus * 2);
484 for (cpu = 0; cpu < nr_cpus; cpu++) {
485 if (pipe2(&pipefd[cpu*2], O_CLOEXEC | O_NONBLOCK)) {
491 if (posix_memalign(&area, page_size, page_size)) {
492 fprintf(stderr, "out of memory\n");
496 bzero(zeropage, page_size);
498 pthread_mutex_lock(&uffd_read_mutex);
500 pthread_attr_init(&attr);
501 pthread_attr_setstacksize(&attr, 16*1024*1024);
505 unsigned long expected_ioctls;
507 printf("bounces: %d, mode:", bounces);
508 if (bounces & BOUNCE_RANDOM)
510 if (bounces & BOUNCE_RACINGFAULTS)
512 if (bounces & BOUNCE_VERIFY)
514 if (bounces & BOUNCE_POLL)
519 if (bounces & BOUNCE_POLL)
520 fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
522 fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
525 uffdio_register.range.start = (unsigned long) area_dst;
526 uffdio_register.range.len = nr_pages * page_size;
527 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
528 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
529 fprintf(stderr, "register failure\n");
532 expected_ioctls = (1 << _UFFDIO_WAKE) |
533 (1 << _UFFDIO_COPY) |
534 (1 << _UFFDIO_ZEROPAGE);
535 if ((uffdio_register.ioctls & expected_ioctls) !=
538 "unexpected missing ioctl for anon memory\n");
543 * The madvise done previously isn't enough: some
544 * uffd_thread could have read userfaults (one of
545 * those already resolved by the background thread)
546 * and it may be in the process of calling
547 * UFFDIO_COPY. UFFDIO_COPY will read the zapped
548 * area_src and it would map a zero page in it (of
549 * course such a UFFDIO_COPY is perfectly safe as it'd
550 * return -EEXIST). The problem comes at the next
551 * bounce though: that racing UFFDIO_COPY would
552 * generate zeropages in the area_src, so invalidating
553 * the previous MADV_DONTNEED. Without this additional
554 * MADV_DONTNEED those zeropages leftovers in the
555 * area_src would lead to -EEXIST failure during the
556 * next bounce, effectively leaving a zeropage in the
559 * Try to comment this out madvise to see the memory
560 * corruption being caught pretty quick.
562 * khugepaged is also inhibited to collapse THP after
563 * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
564 * required to MADV_DONTNEED here.
566 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
572 if (stress(userfaults))
576 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
577 fprintf(stderr, "register failure\n");
582 if (bounces & BOUNCE_VERIFY) {
583 for (nr = 0; nr < nr_pages; nr++) {
584 if (*area_count(area_dst, nr) != count_verify[nr]) {
586 "error area_count %Lu %Lu %lu\n",
587 *area_count(area_src, nr),
596 /* prepare next bounce */
601 printf("userfaults:");
602 for (cpu = 0; cpu < nr_cpus; cpu++)
603 printf(" %lu", userfaults[cpu]);
610 int main(int argc, char **argv)
613 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
614 nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
615 page_size = sysconf(_SC_PAGE_SIZE);
616 if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) * 2
618 fprintf(stderr, "Impossible to run this test\n"), exit(2);
619 nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
621 if (!nr_pages_per_cpu) {
622 fprintf(stderr, "invalid MiB\n");
623 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
625 bounces = atoi(argv[2]);
627 fprintf(stderr, "invalid bounces\n");
628 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
630 nr_pages = nr_pages_per_cpu * nr_cpus;
631 printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
632 nr_pages, nr_pages_per_cpu);
633 return userfaultfd_stress();
636 #else /* __NR_userfaultfd */
638 #warning "missing __NR_userfaultfd definition"
642 printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
646 #endif /* __NR_userfaultfd */