tools/testing/selftests/vm/userfaultfd.c

   1 /*
   2  * Stress userfaultfd syscall.
   3  *
   4  *  Copyright (C) 2015  Red Hat, Inc.
   5  *
   6  *  This work is licensed under the terms of the GNU GPL, version 2. See
   7  *  the COPYING file in the top-level directory.
   8  *
   9  * This test allocates two virtual areas and bounces the physical
  10  * memory across the two virtual areas (from area_src to area_dst)
  11  * using userfaultfd.
  12  *
  13  * There are three threads running per CPU:
  14  *
  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.
  19  *
  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.
  23  *
  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
  27  *    area.
  28  *
  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
  32  * opposite direction.
  33  *
  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).
  37  *
  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.
  40  *
  41  * # 100MiB 99999 bounces
  42  * ./userfaultfd 100 99999
  43  *
  44  * # 1GiB 99 bounces
  45  * ./userfaultfd 1000 99
  46  *
  47  * # 10MiB-~6GiB 999 bounces, continue forever unless an error triggers
  48  * while ./userfaultfd $[RANDOM % 6000 + 10] 999; do true; done
  49  */
  50
  51 #define _GNU_SOURCE
  52 #include <stdio.h>
  53 #include <errno.h>
  54 #include <unistd.h>
  55 #include <stdlib.h>
  56 #include <sys/types.h>
  57 #include <sys/stat.h>
  58 #include <fcntl.h>
  59 #include <time.h>
  60 #include <signal.h>
  61 #include <poll.h>
  62 #include <string.h>
  63 #include <linux/mman.h>
  64 #include <sys/mman.h>
  65 #include <sys/syscall.h>
  66 #include <sys/ioctl.h>
  67 #include <pthread.h>
  68 #include <linux/userfaultfd.h>
  69
  70 #ifdef __NR_userfaultfd
  71
  72 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
  73
  74 #define BOUNCE_RANDOM           (1<<0)
  75 #define BOUNCE_RACINGFAULTS     (1<<1)
  76 #define BOUNCE_VERIFY           (1<<2)
  77 #define BOUNCE_POLL             (1<<3)
  78 static int bounces;
  79
  80 static unsigned long long *count_verify;
  81 static int uffd, finished, *pipefd;
  82 static char *area_src, *area_dst;
  83 static char *zeropage;
  84 pthread_attr_t attr;
  85
  86 /* pthread_mutex_t starts at page offset 0 */
  87 #define area_mutex(___area, ___nr)                                      \
  88         ((pthread_mutex_t *) ((___area) + (___nr)*page_size))
  89 /*
  90  * count is placed in the page after pthread_mutex_t naturally aligned
  91  * to avoid non alignment faults on non-x86 archs.
  92  */
  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) \
  99                                                   -  1)))
 100
 101 static int my_bcmp(char *str1, char *str2, size_t n)
 102 {
 103         unsigned long i;
 104         for (i = 0; i < n; i++)
 105                 if (str1[i] != str2[i])
 106                         return 1;
 107         return 0;
 108 }
 109
 110 static void *locking_thread(void *arg)
 111 {
 112         unsigned long cpu = (unsigned long) arg;
 113         struct random_data rand;
 114         unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
 115         int32_t rand_nr;
 116         unsigned long long count;
 117         char randstate[64];
 118         unsigned int seed;
 119         time_t start;
 120
 121         if (bounces & BOUNCE_RANDOM) {
 122                 seed = (unsigned int) time(NULL) - bounces;
 123                 if (!(bounces & BOUNCE_RACINGFAULTS))
 124                         seed += cpu;
 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);
 129         } else {
 130                 page_nr = -bounces;
 131                 if (!(bounces & BOUNCE_RACINGFAULTS))
 132                         page_nr += cpu * nr_pages_per_cpu;
 133         }
 134
 135         while (!finished) {
 136                 if (bounces & BOUNCE_RANDOM) {
 137                         if (random_r(&rand, &rand_nr))
 138                                 fprintf(stderr, "random_r 1 error\n"), exit(1);
 139                         page_nr = rand_nr;
 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) <<
 144                                            16;
 145                         }
 146                 } else
 147                         page_nr += 1;
 148                 page_nr %= nr_pages;
 149
 150                 start = time(NULL);
 151                 if (bounces & BOUNCE_VERIFY) {
 152                         count = *area_count(area_dst, page_nr);
 153                         if (!count)
 154                                 fprintf(stderr,
 155                                         "page_nr %lu wrong count %Lu %Lu\n",
 156                                         page_nr, count,
 157                                         count_verify[page_nr]), exit(1);
 158
 159
 160                         /*
 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
 165                          * different).
 166                          */
 167 #if 1
 168                         if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
 169                                      page_size))
 170                                 fprintf(stderr,
 171                                         "my_bcmp page_nr %lu wrong count %Lu %Lu\n",
 172                                         page_nr, count,
 173                                         count_verify[page_nr]), exit(1);
 174 #else
 175                         unsigned long loops;
 176
 177                         loops = 0;
 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,
 181                                      page_size)) {
 182                                 loops += 1;
 183                                 if (loops > 10)
 184                                         break;
 185                         }
 186                         /* uncomment below line to test with mutex */
 187                         /* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
 188                         if (loops) {
 189                                 fprintf(stderr,
 190                                         "page_nr %lu all zero thread %lu %p %lu\n",
 191                                         page_nr, cpu, area_dst + page_nr * page_size,
 192                                         loops);
 193                                 if (loops > 10)
 194                                         exit(1);
 195                         }
 196 #endif
 197                 }
 198
 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]) {
 202                         fprintf(stderr,
 203                                 "page_nr %lu memory corruption %Lu %Lu\n",
 204                                 page_nr, count,
 205                                 count_verify[page_nr]), exit(1);
 206                 }
 207                 count++;
 208                 *area_count(area_dst, page_nr) = count_verify[page_nr] = count;
 209                 pthread_mutex_unlock(area_mutex(area_dst, page_nr));
 210
 211                 if (time(NULL) - start > 1)
 212                         fprintf(stderr,
 213                                 "userfault too slow %ld "
 214                                 "possible false positive with overcommit\n",
 215                                 time(NULL) - start);
 216         }
 217
 218         return NULL;
 219 }
 220
 221 static int copy_page(unsigned long offset)
 222 {
 223         struct uffdio_copy uffdio_copy;
 224
 225         if (offset >= nr_pages * page_size)
 226                 fprintf(stderr, "unexpected offset %lu\n",
 227                         offset), exit(1);
 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);
 241         } else
 242                 return 1;
 243         return 0;
 244 }
 245
 246 static void *uffd_poll_thread(void *arg)
 247 {
 248         unsigned long cpu = (unsigned long) arg;
 249         struct pollfd pollfd[2];
 250         struct uffd_msg msg;
 251         int ret;
 252         unsigned long offset;
 253         char tmp_chr;
 254         unsigned long userfaults = 0;
 255
 256         pollfd[0].fd = uffd;
 257         pollfd[0].events = POLLIN;
 258         pollfd[1].fd = pipefd[cpu*2];
 259         pollfd[1].events = POLLIN;
 260
 261         for (;;) {
 262                 ret = poll(pollfd, 2, -1);
 263                 if (!ret)
 264                         fprintf(stderr, "poll error %d\n", ret), exit(1);
 265                 if (ret < 0)
 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"),
 270                                         exit(1);
 271                         break;
 272                 }
 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));
 277                 if (ret < 0) {
 278                         if (errno == EAGAIN)
 279                                 continue;
 280                         perror("nonblocking read error"), exit(1);
 281                 }
 282                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 283                         fprintf(stderr, "unexpected msg event %u\n",
 284                                 msg.event), exit(1);
 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 -
 288                          area_dst;
 289                 offset &= ~(page_size-1);
 290                 if (copy_page(offset))
 291                         userfaults++;
 292         }
 293         return (void *)userfaults;
 294 }
 295
 296 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
 297
 298 static void *uffd_read_thread(void *arg)
 299 {
 300         unsigned long *this_cpu_userfaults;
 301         struct uffd_msg msg;
 302         unsigned long offset;
 303         int ret;
 304
 305         this_cpu_userfaults = (unsigned long *) arg;
 306         *this_cpu_userfaults = 0;
 307
 308         pthread_mutex_unlock(&uffd_read_mutex);
 309         /* from here cancellation is ok */
 310
 311         for (;;) {
 312                 ret = read(uffd, &msg, sizeof(msg));
 313                 if (ret != sizeof(msg)) {
 314                         if (ret < 0)
 315                                 perror("blocking read error"), exit(1);
 316                         else
 317                                 fprintf(stderr, "short read\n"), exit(1);
 318                 }
 319                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 320                         fprintf(stderr, "unexpected msg event %u\n",
 321                                 msg.event), exit(1);
 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 -
 326                          area_dst;
 327                 offset &= ~(page_size-1);
 328                 if (copy_page(offset))
 329                         (*this_cpu_userfaults)++;
 330         }
 331         return (void *)NULL;
 332 }
 333
 334 static void *background_thread(void *arg)
 335 {
 336         unsigned long cpu = (unsigned long) arg;
 337         unsigned long page_nr;
 338
 339         for (page_nr = cpu * nr_pages_per_cpu;
 340              page_nr < (cpu+1) * nr_pages_per_cpu;
 341              page_nr++)
 342                 copy_page(page_nr * page_size);
 343
 344         return NULL;
 345 }
 346
 347 static int stress(unsigned long *userfaults)
 348 {
 349         unsigned long cpu;
 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;
 354
 355         finished = 0;
 356         for (cpu = 0; cpu < nr_cpus; cpu++) {
 357                 if (pthread_create(&locking_threads[cpu], &attr,
 358                                    locking_thread, (void *)cpu))
 359                         return 1;
 360                 if (bounces & BOUNCE_POLL) {
 361                         if (pthread_create(&uffd_threads[cpu], &attr,
 362                                            uffd_poll_thread, (void *)cpu))
 363                                 return 1;
 364                 } else {
 365                         if (pthread_create(&uffd_threads[cpu], &attr,
 366                                            uffd_read_thread,
 367                                            &_userfaults[cpu]))
 368                                 return 1;
 369                         pthread_mutex_lock(&uffd_read_mutex);
 370                 }
 371                 if (pthread_create(&background_threads[cpu], &attr,
 372                                    background_thread, (void *)cpu))
 373                         return 1;
 374         }
 375         for (cpu = 0; cpu < nr_cpus; cpu++)
 376                 if (pthread_join(background_threads[cpu], NULL))
 377                         return 1;
 378
 379         /*
 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).
 387          */
 388         if (madvise(area_src, nr_pages * page_size, MADV_DONTNEED)) {
 389                 perror("madvise");
 390                 return 1;
 391         }
 392
 393         for (cpu = 0; cpu < nr_cpus; cpu++) {
 394                 char c;
 395                 if (bounces & BOUNCE_POLL) {
 396                         if (write(pipefd[cpu*2+1], &c, 1) != 1) {
 397                                 fprintf(stderr, "pipefd write error\n");
 398                                 return 1;
 399                         }
 400                         if (pthread_join(uffd_threads[cpu], &_userfaults[cpu]))
 401                                 return 1;
 402                 } else {
 403                         if (pthread_cancel(uffd_threads[cpu]))
 404                                 return 1;
 405                         if (pthread_join(uffd_threads[cpu], NULL))
 406                                 return 1;
 407                 }
 408         }
 409
 410         finished = 1;
 411         for (cpu = 0; cpu < nr_cpus; cpu++)
 412                 if (pthread_join(locking_threads[cpu], NULL))
 413                         return 1;
 414
 415         return 0;
 416 }
 417
 418 static int userfaultfd_stress(void)
 419 {
 420         void *area;
 421         char *tmp_area;
 422         unsigned long nr;
 423         struct uffdio_register uffdio_register;
 424         struct uffdio_api uffdio_api;
 425         unsigned long cpu;
 426         int uffd_flags, err;
 427         unsigned long userfaults[nr_cpus];
 428
 429         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 430                 fprintf(stderr, "out of memory\n");
 431                 return 1;
 432         }
 433         area_src = area;
 434         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 435                 fprintf(stderr, "out of memory\n");
 436                 return 1;
 437         }
 438         area_dst = area;
 439
 440         uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 441         if (uffd < 0) {
 442                 fprintf(stderr,
 443                         "userfaultfd syscall not available in this kernel\n");
 444                 return 1;
 445         }
 446         uffd_flags = fcntl(uffd, F_GETFD, NULL);
 447
 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");
 452                 return 1;
 453         }
 454         if (uffdio_api.api != UFFD_API) {
 455                 fprintf(stderr, "UFFDIO_API error %Lu\n", uffdio_api.api);
 456                 return 1;
 457         }
 458
 459         count_verify = malloc(nr_pages * sizeof(unsigned long long));
 460         if (!count_verify) {
 461                 perror("count_verify");
 462                 return 1;
 463         }
 464
 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;
 469                 /*
 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
 474                  * positives.
 475                  */
 476                 *(area_count(area_src, nr) + 1) = 1;
 477         }
 478
 479         pipefd = malloc(sizeof(int) * nr_cpus * 2);
 480         if (!pipefd) {
 481                 perror("pipefd");
 482                 return 1;
 483         }
 484         for (cpu = 0; cpu < nr_cpus; cpu++) {
 485                 if (pipe2(&pipefd[cpu*2], O_CLOEXEC | O_NONBLOCK)) {
 486                         perror("pipe");
 487                         return 1;
 488                 }
 489         }
 490
 491         if (posix_memalign(&area, page_size, page_size)) {
 492                 fprintf(stderr, "out of memory\n");
 493                 return 1;
 494         }
 495         zeropage = area;
 496         bzero(zeropage, page_size);
 497
 498         pthread_mutex_lock(&uffd_read_mutex);
 499
 500         pthread_attr_init(&attr);
 501         pthread_attr_setstacksize(&attr, 16*1024*1024);
 502
 503         err = 0;
 504         while (bounces--) {
 505                 unsigned long expected_ioctls;
 506
 507                 printf("bounces: %d, mode:", bounces);
 508                 if (bounces & BOUNCE_RANDOM)
 509                         printf(" rnd");
 510                 if (bounces & BOUNCE_RACINGFAULTS)
 511                         printf(" racing");
 512                 if (bounces & BOUNCE_VERIFY)
 513                         printf(" ver");
 514                 if (bounces & BOUNCE_POLL)
 515                         printf(" poll");
 516                 printf(", ");
 517                 fflush(stdout);
 518
 519                 if (bounces & BOUNCE_POLL)
 520                         fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 521                 else
 522                         fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
 523
 524                 /* register */
 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");
 530                         return 1;
 531                 }
 532                 expected_ioctls = (1 << _UFFDIO_WAKE) |
 533                                   (1 << _UFFDIO_COPY) |
 534                                   (1 << _UFFDIO_ZEROPAGE);
 535                 if ((uffdio_register.ioctls & expected_ioctls) !=
 536                     expected_ioctls) {
 537                         fprintf(stderr,
 538                                 "unexpected missing ioctl for anon memory\n");
 539                         return 1;
 540                 }
 541
 542                 /*
 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
 557                  * area_dst.
 558                  *
 559                  * Try to comment this out madvise to see the memory
 560                  * corruption being caught pretty quick.
 561                  *
 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.
 565                  */
 566                 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
 567                         perror("madvise 2");
 568                         return 1;
 569                 }
 570
 571                 /* bounce pass */
 572                 if (stress(userfaults))
 573                         return 1;
 574
 575                 /* unregister */
 576                 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
 577                         fprintf(stderr, "register failure\n");
 578                         return 1;
 579                 }
 580
 581                 /* verification */
 582                 if (bounces & BOUNCE_VERIFY) {
 583                         for (nr = 0; nr < nr_pages; nr++) {
 584                                 if (*area_count(area_dst, nr) != count_verify[nr]) {
 585                                         fprintf(stderr,
 586                                                 "error area_count %Lu %Lu %lu\n",
 587                                                 *area_count(area_src, nr),
 588                                                 count_verify[nr],
 589                                                 nr);
 590                                         err = 1;
 591                                         bounces = 0;
 592                                 }
 593                         }
 594                 }
 595
 596                 /* prepare next bounce */
 597                 tmp_area = area_src;
 598                 area_src = area_dst;
 599                 area_dst = tmp_area;
 600
 601                 printf("userfaults:");
 602                 for (cpu = 0; cpu < nr_cpus; cpu++)
 603                         printf(" %lu", userfaults[cpu]);
 604                 printf("\n");
 605         }
 606
 607         return err;
 608 }
 609
 610 int main(int argc, char **argv)
 611 {
 612         if (argc < 3)
 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
 617             > page_size)
 618                 fprintf(stderr, "Impossible to run this test\n"), exit(2);
 619         nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
 620                 nr_cpus;
 621         if (!nr_pages_per_cpu) {
 622                 fprintf(stderr, "invalid MiB\n");
 623                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 624         }
 625         bounces = atoi(argv[2]);
 626         if (bounces <= 0) {
 627                 fprintf(stderr, "invalid bounces\n");
 628                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 629         }
 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();
 634 }
 635
 636 #else /* __NR_userfaultfd */
 637
 638 #warning "missing __NR_userfaultfd definition"
 639
 640 int main(void)
 641 {
 642         printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
 643         return 0;
 644 }
 645
 646 #endif /* __NR_userfaultfd */