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 <sys/mman.h>
  64 #include <sys/syscall.h>
  65 #include <sys/ioctl.h>
  66 #include <pthread.h>
  67 #include <linux/userfaultfd.h>
  68
  69 #ifndef __NR_userfaultfd
  70 #ifdef __x86_64__
  71 #define __NR_userfaultfd 323
  72 #elif defined(__i386__)
  73 #define __NR_userfaultfd 374
  74 #elif defined(__powewrpc__)
  75 #define __NR_userfaultfd 364
  76 #elif defined(__s390__)
  77 #define __NR_userfaultfd 355
  78 #else
  79 #error "missing __NR_userfaultfd definition"
  80 #endif
  81 #endif
  82
  83 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
  84
  85 #define BOUNCE_RANDOM           (1<<0)
  86 #define BOUNCE_RACINGFAULTS     (1<<1)
  87 #define BOUNCE_VERIFY           (1<<2)
  88 #define BOUNCE_POLL             (1<<3)
  89 static int bounces;
  90
  91 static unsigned long long *count_verify;
  92 static int uffd, finished, *pipefd;
  93 static char *area_src, *area_dst;
  94 static char *zeropage;
  95 pthread_attr_t attr;
  96
  97 /* pthread_mutex_t starts at page offset 0 */
  98 #define area_mutex(___area, ___nr)                                      \
  99         ((pthread_mutex_t *) ((___area) + (___nr)*page_size))
 100 /*
 101  * count is placed in the page after pthread_mutex_t naturally aligned
 102  * to avoid non alignment faults on non-x86 archs.
 103  */
 104 #define area_count(___area, ___nr)                                      \
 105         ((volatile unsigned long long *) ((unsigned long)               \
 106                                  ((___area) + (___nr)*page_size +       \
 107                                   sizeof(pthread_mutex_t) +             \
 108                                   sizeof(unsigned long long) - 1) &     \
 109                                  ~(unsigned long)(sizeof(unsigned long long) \
 110                                                   -  1)))
 111
 112 static int my_bcmp(char *str1, char *str2, size_t n)
 113 {
 114         unsigned long i;
 115         for (i = 0; i < n; i++)
 116                 if (str1[i] != str2[i])
 117                         return 1;
 118         return 0;
 119 }
 120
 121 static void *locking_thread(void *arg)
 122 {
 123         unsigned long cpu = (unsigned long) arg;
 124         struct random_data rand;
 125         unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
 126         int32_t rand_nr;
 127         unsigned long long count;
 128         char randstate[64];
 129         unsigned int seed;
 130         time_t start;
 131
 132         if (bounces & BOUNCE_RANDOM) {
 133                 seed = (unsigned int) time(NULL) - bounces;
 134                 if (!(bounces & BOUNCE_RACINGFAULTS))
 135                         seed += cpu;
 136                 bzero(&rand, sizeof(rand));
 137                 bzero(&randstate, sizeof(randstate));
 138                 if (initstate_r(seed, randstate, sizeof(randstate), &rand))
 139                         fprintf(stderr, "srandom_r error\n"), exit(1);
 140         } else {
 141                 page_nr = -bounces;
 142                 if (!(bounces & BOUNCE_RACINGFAULTS))
 143                         page_nr += cpu * nr_pages_per_cpu;
 144         }
 145
 146         while (!finished) {
 147                 if (bounces & BOUNCE_RANDOM) {
 148                         if (random_r(&rand, &rand_nr))
 149                                 fprintf(stderr, "random_r 1 error\n"), exit(1);
 150                         page_nr = rand_nr;
 151                         if (sizeof(page_nr) > sizeof(rand_nr)) {
 152                                 if (random_r(&rand, &rand_nr))
 153                                         fprintf(stderr, "random_r 2 error\n"), exit(1);
 154                                 page_nr |= (((unsigned long) rand_nr) << 16) <<
 155                                            16;
 156                         }
 157                 } else
 158                         page_nr += 1;
 159                 page_nr %= nr_pages;
 160
 161                 start = time(NULL);
 162                 if (bounces & BOUNCE_VERIFY) {
 163                         count = *area_count(area_dst, page_nr);
 164                         if (!count)
 165                                 fprintf(stderr,
 166                                         "page_nr %lu wrong count %Lu %Lu\n",
 167                                         page_nr, count,
 168                                         count_verify[page_nr]), exit(1);
 169
 170
 171                         /*
 172                          * We can't use bcmp (or memcmp) because that
 173                          * returns 0 erroneously if the memory is
 174                          * changing under it (even if the end of the
 175                          * page is never changing and always
 176                          * different).
 177                          */
 178 #if 1
 179                         if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
 180                                      page_size))
 181                                 fprintf(stderr,
 182                                         "my_bcmp page_nr %lu wrong count %Lu %Lu\n",
 183                                         page_nr, count,
 184                                         count_verify[page_nr]), exit(1);
 185 #else
 186                         unsigned long loops;
 187
 188                         loops = 0;
 189                         /* uncomment the below line to test with mutex */
 190                         /* pthread_mutex_lock(area_mutex(area_dst, page_nr)); */
 191                         while (!bcmp(area_dst + page_nr * page_size, zeropage,
 192                                      page_size)) {
 193                                 loops += 1;
 194                                 if (loops > 10)
 195                                         break;
 196                         }
 197                         /* uncomment below line to test with mutex */
 198                         /* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
 199                         if (loops) {
 200                                 fprintf(stderr,
 201                                         "page_nr %lu all zero thread %lu %p %lu\n",
 202                                         page_nr, cpu, area_dst + page_nr * page_size,
 203                                         loops);
 204                                 if (loops > 10)
 205                                         exit(1);
 206                         }
 207 #endif
 208                 }
 209
 210                 pthread_mutex_lock(area_mutex(area_dst, page_nr));
 211                 count = *area_count(area_dst, page_nr);
 212                 if (count != count_verify[page_nr]) {
 213                         fprintf(stderr,
 214                                 "page_nr %lu memory corruption %Lu %Lu\n",
 215                                 page_nr, count,
 216                                 count_verify[page_nr]), exit(1);
 217                 }
 218                 count++;
 219                 *area_count(area_dst, page_nr) = count_verify[page_nr] = count;
 220                 pthread_mutex_unlock(area_mutex(area_dst, page_nr));
 221
 222                 if (time(NULL) - start > 1)
 223                         fprintf(stderr,
 224                                 "userfault too slow %ld "
 225                                 "possible false positive with overcommit\n",
 226                                 time(NULL) - start);
 227         }
 228
 229         return NULL;
 230 }
 231
 232 static int copy_page(unsigned long offset)
 233 {
 234         struct uffdio_copy uffdio_copy;
 235
 236         if (offset >= nr_pages * page_size)
 237                 fprintf(stderr, "unexpected offset %lu\n",
 238                         offset), exit(1);
 239         uffdio_copy.dst = (unsigned long) area_dst + offset;
 240         uffdio_copy.src = (unsigned long) area_src + offset;
 241         uffdio_copy.len = page_size;
 242         uffdio_copy.mode = 0;
 243         uffdio_copy.copy = 0;
 244         if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy)) {
 245                 /* real retval in ufdio_copy.copy */
 246                 if (uffdio_copy.copy != -EEXIST)
 247                         fprintf(stderr, "UFFDIO_COPY error %Ld\n",
 248                                 uffdio_copy.copy), exit(1);
 249         } else if (uffdio_copy.copy != page_size) {
 250                 fprintf(stderr, "UFFDIO_COPY unexpected copy %Ld\n",
 251                         uffdio_copy.copy), exit(1);
 252         } else
 253                 return 1;
 254         return 0;
 255 }
 256
 257 static void *uffd_poll_thread(void *arg)
 258 {
 259         unsigned long cpu = (unsigned long) arg;
 260         struct pollfd pollfd[2];
 261         struct uffd_msg msg;
 262         int ret;
 263         unsigned long offset;
 264         char tmp_chr;
 265         unsigned long userfaults = 0;
 266
 267         pollfd[0].fd = uffd;
 268         pollfd[0].events = POLLIN;
 269         pollfd[1].fd = pipefd[cpu*2];
 270         pollfd[1].events = POLLIN;
 271
 272         for (;;) {
 273                 ret = poll(pollfd, 2, -1);
 274                 if (!ret)
 275                         fprintf(stderr, "poll error %d\n", ret), exit(1);
 276                 if (ret < 0)
 277                         perror("poll"), exit(1);
 278                 if (pollfd[1].revents & POLLIN) {
 279                         if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
 280                                 fprintf(stderr, "read pipefd error\n"),
 281                                         exit(1);
 282                         break;
 283                 }
 284                 if (!(pollfd[0].revents & POLLIN))
 285                         fprintf(stderr, "pollfd[0].revents %d\n",
 286                                 pollfd[0].revents), exit(1);
 287                 ret = read(uffd, &msg, sizeof(msg));
 288                 if (ret < 0) {
 289                         if (errno == EAGAIN)
 290                                 continue;
 291                         perror("nonblocking read error"), exit(1);
 292                 }
 293                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 294                         fprintf(stderr, "unexpected msg event %u\n",
 295                                 msg.event), exit(1);
 296                 if (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 297                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 298                 offset = (char *)(unsigned long)msg.arg.pagefault.address -
 299                          area_dst;
 300                 offset &= ~(page_size-1);
 301                 if (copy_page(offset))
 302                         userfaults++;
 303         }
 304         return (void *)userfaults;
 305 }
 306
 307 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
 308
 309 static void *uffd_read_thread(void *arg)
 310 {
 311         unsigned long *this_cpu_userfaults;
 312         struct uffd_msg msg;
 313         unsigned long offset;
 314         int ret;
 315
 316         this_cpu_userfaults = (unsigned long *) arg;
 317         *this_cpu_userfaults = 0;
 318
 319         pthread_mutex_unlock(&uffd_read_mutex);
 320         /* from here cancellation is ok */
 321
 322         for (;;) {
 323                 ret = read(uffd, &msg, sizeof(msg));
 324                 if (ret != sizeof(msg)) {
 325                         if (ret < 0)
 326                                 perror("blocking read error"), exit(1);
 327                         else
 328                                 fprintf(stderr, "short read\n"), exit(1);
 329                 }
 330                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 331                         fprintf(stderr, "unexpected msg event %u\n",
 332                                 msg.event), exit(1);
 333                 if (bounces & BOUNCE_VERIFY &&
 334                     msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 335                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 336                 offset = (char *)(unsigned long)msg.arg.pagefault.address -
 337                          area_dst;
 338                 offset &= ~(page_size-1);
 339                 if (copy_page(offset))
 340                         (*this_cpu_userfaults)++;
 341         }
 342         return (void *)NULL;
 343 }
 344
 345 static void *background_thread(void *arg)
 346 {
 347         unsigned long cpu = (unsigned long) arg;
 348         unsigned long page_nr;
 349
 350         for (page_nr = cpu * nr_pages_per_cpu;
 351              page_nr < (cpu+1) * nr_pages_per_cpu;
 352              page_nr++)
 353                 copy_page(page_nr * page_size);
 354
 355         return NULL;
 356 }
 357
 358 static int stress(unsigned long *userfaults)
 359 {
 360         unsigned long cpu;
 361         pthread_t locking_threads[nr_cpus];
 362         pthread_t uffd_threads[nr_cpus];
 363         pthread_t background_threads[nr_cpus];
 364         void **_userfaults = (void **) userfaults;
 365
 366         finished = 0;
 367         for (cpu = 0; cpu < nr_cpus; cpu++) {
 368                 if (pthread_create(&locking_threads[cpu], &attr,
 369                                    locking_thread, (void *)cpu))
 370                         return 1;
 371                 if (bounces & BOUNCE_POLL) {
 372                         if (pthread_create(&uffd_threads[cpu], &attr,
 373                                            uffd_poll_thread, (void *)cpu))
 374                                 return 1;
 375                 } else {
 376                         if (pthread_create(&uffd_threads[cpu], &attr,
 377                                            uffd_read_thread,
 378                                            &_userfaults[cpu]))
 379                                 return 1;
 380                         pthread_mutex_lock(&uffd_read_mutex);
 381                 }
 382                 if (pthread_create(&background_threads[cpu], &attr,
 383                                    background_thread, (void *)cpu))
 384                         return 1;
 385         }
 386         for (cpu = 0; cpu < nr_cpus; cpu++)
 387                 if (pthread_join(background_threads[cpu], NULL))
 388                         return 1;
 389
 390         /*
 391          * Be strict and immediately zap area_src, the whole area has
 392          * been transferred already by the background treads. The
 393          * area_src could then be faulted in in a racy way by still
 394          * running uffdio_threads reading zeropages after we zapped
 395          * area_src (but they're guaranteed to get -EEXIST from
 396          * UFFDIO_COPY without writing zero pages into area_dst
 397          * because the background threads already completed).
 398          */
 399         if (madvise(area_src, nr_pages * page_size, MADV_DONTNEED)) {
 400                 perror("madvise");
 401                 return 1;
 402         }
 403
 404         for (cpu = 0; cpu < nr_cpus; cpu++) {
 405                 char c;
 406                 if (bounces & BOUNCE_POLL) {
 407                         if (write(pipefd[cpu*2+1], &c, 1) != 1) {
 408                                 fprintf(stderr, "pipefd write error\n");
 409                                 return 1;
 410                         }
 411                         if (pthread_join(uffd_threads[cpu], &_userfaults[cpu]))
 412                                 return 1;
 413                 } else {
 414                         if (pthread_cancel(uffd_threads[cpu]))
 415                                 return 1;
 416                         if (pthread_join(uffd_threads[cpu], NULL))
 417                                 return 1;
 418                 }
 419         }
 420
 421         finished = 1;
 422         for (cpu = 0; cpu < nr_cpus; cpu++)
 423                 if (pthread_join(locking_threads[cpu], NULL))
 424                         return 1;
 425
 426         return 0;
 427 }
 428
 429 static int userfaultfd_stress(void)
 430 {
 431         void *area;
 432         char *tmp_area;
 433         unsigned long nr;
 434         struct uffdio_register uffdio_register;
 435         struct uffdio_api uffdio_api;
 436         unsigned long cpu;
 437         int uffd_flags;
 438         unsigned long userfaults[nr_cpus];
 439
 440         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 441                 fprintf(stderr, "out of memory\n");
 442                 return 1;
 443         }
 444         area_src = area;
 445         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 446                 fprintf(stderr, "out of memory\n");
 447                 return 1;
 448         }
 449         area_dst = area;
 450
 451         uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 452         if (uffd < 0) {
 453                 fprintf(stderr,
 454                         "userfaultfd syscall not available in this kernel\n");
 455                 return 1;
 456         }
 457         uffd_flags = fcntl(uffd, F_GETFD, NULL);
 458
 459         uffdio_api.api = UFFD_API;
 460         uffdio_api.features = 0;
 461         if (ioctl(uffd, UFFDIO_API, &uffdio_api)) {
 462                 fprintf(stderr, "UFFDIO_API\n");
 463                 return 1;
 464         }
 465         if (uffdio_api.api != UFFD_API) {
 466                 fprintf(stderr, "UFFDIO_API error %Lu\n", uffdio_api.api);
 467                 return 1;
 468         }
 469
 470         count_verify = malloc(nr_pages * sizeof(unsigned long long));
 471         if (!count_verify) {
 472                 perror("count_verify");
 473                 return 1;
 474         }
 475
 476         for (nr = 0; nr < nr_pages; nr++) {
 477                 *area_mutex(area_src, nr) = (pthread_mutex_t)
 478                         PTHREAD_MUTEX_INITIALIZER;
 479                 count_verify[nr] = *area_count(area_src, nr) = 1;
 480         }
 481
 482         pipefd = malloc(sizeof(int) * nr_cpus * 2);
 483         if (!pipefd) {
 484                 perror("pipefd");
 485                 return 1;
 486         }
 487         for (cpu = 0; cpu < nr_cpus; cpu++) {
 488                 if (pipe2(&pipefd[cpu*2], O_CLOEXEC | O_NONBLOCK)) {
 489                         perror("pipe");
 490                         return 1;
 491                 }
 492         }
 493
 494         if (posix_memalign(&area, page_size, page_size)) {
 495                 fprintf(stderr, "out of memory\n");
 496                 return 1;
 497         }
 498         zeropage = area;
 499         bzero(zeropage, page_size);
 500
 501         pthread_mutex_lock(&uffd_read_mutex);
 502
 503         pthread_attr_init(&attr);
 504         pthread_attr_setstacksize(&attr, 16*1024*1024);
 505
 506         while (bounces--) {
 507                 unsigned long expected_ioctls;
 508
 509                 printf("bounces: %d, mode:", bounces);
 510                 if (bounces & BOUNCE_RANDOM)
 511                         printf(" rnd");
 512                 if (bounces & BOUNCE_RACINGFAULTS)
 513                         printf(" racing");
 514                 if (bounces & BOUNCE_VERIFY)
 515                         printf(" ver");
 516                 if (bounces & BOUNCE_POLL)
 517                         printf(" poll");
 518                 printf(", ");
 519                 fflush(stdout);
 520
 521                 if (bounces & BOUNCE_POLL)
 522                         fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 523                 else
 524                         fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
 525
 526                 /* register */
 527                 uffdio_register.range.start = (unsigned long) area_dst;
 528                 uffdio_register.range.len = nr_pages * page_size;
 529                 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
 530                 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
 531                         fprintf(stderr, "register failure\n");
 532                         return 1;
 533                 }
 534                 expected_ioctls = (1 << _UFFDIO_WAKE) |
 535                                   (1 << _UFFDIO_COPY) |
 536                                   (1 << _UFFDIO_ZEROPAGE);
 537                 if ((uffdio_register.ioctls & expected_ioctls) !=
 538                     expected_ioctls) {
 539                         fprintf(stderr,
 540                                 "unexpected missing ioctl for anon memory\n");
 541                         return 1;
 542                 }
 543
 544                 /*
 545                  * The madvise done previously isn't enough: some
 546                  * uffd_thread could have read userfaults (one of
 547                  * those already resolved by the background thread)
 548                  * and it may be in the process of calling
 549                  * UFFDIO_COPY. UFFDIO_COPY will read the zapped
 550                  * area_src and it would map a zero page in it (of
 551                  * course such a UFFDIO_COPY is perfectly safe as it'd
 552                  * return -EEXIST). The problem comes at the next
 553                  * bounce though: that racing UFFDIO_COPY would
 554                  * generate zeropages in the area_src, so invalidating
 555                  * the previous MADV_DONTNEED. Without this additional
 556                  * MADV_DONTNEED those zeropages leftovers in the
 557                  * area_src would lead to -EEXIST failure during the
 558                  * next bounce, effectively leaving a zeropage in the
 559                  * area_dst.
 560                  *
 561                  * Try to comment this out madvise to see the memory
 562                  * corruption being caught pretty quick.
 563                  *
 564                  * khugepaged is also inhibited to collapse THP after
 565                  * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
 566                  * required to MADV_DONTNEED here.
 567                  */
 568                 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
 569                         perror("madvise 2");
 570                         return 1;
 571                 }
 572
 573                 /* bounce pass */
 574                 if (stress(userfaults))
 575                         return 1;
 576
 577                 /* unregister */
 578                 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
 579                         fprintf(stderr, "register failure\n");
 580                         return 1;
 581                 }
 582
 583                 /* verification */
 584                 if (bounces & BOUNCE_VERIFY) {
 585                         for (nr = 0; nr < nr_pages; nr++) {
 586                                 if (my_bcmp(area_dst,
 587                                             area_dst + nr * page_size,
 588                                             sizeof(pthread_mutex_t))) {
 589                                         fprintf(stderr,
 590                                                 "error mutex 2 %lu\n",
 591                                                 nr);
 592                                         bounces = 0;
 593                                 }
 594                                 if (*area_count(area_dst, nr) != count_verify[nr]) {
 595                                         fprintf(stderr,
 596                                                 "error area_count %Lu %Lu %lu\n",
 597                                                 *area_count(area_src, nr),
 598                                                 count_verify[nr],
 599                                                 nr);
 600                                         bounces = 0;
 601                                 }
 602                         }
 603                 }
 604
 605                 /* prepare next bounce */
 606                 tmp_area = area_src;
 607                 area_src = area_dst;
 608                 area_dst = tmp_area;
 609
 610                 printf("userfaults:");
 611                 for (cpu = 0; cpu < nr_cpus; cpu++)
 612                         printf(" %lu", userfaults[cpu]);
 613                 printf("\n");
 614         }
 615
 616         return 0;
 617 }
 618
 619 int main(int argc, char **argv)
 620 {
 621         if (argc < 3)
 622                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 623         nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
 624         page_size = sysconf(_SC_PAGE_SIZE);
 625         if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) >
 626             page_size)
 627                 fprintf(stderr, "Impossible to run this test\n"), exit(2);
 628         nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
 629                 nr_cpus;
 630         if (!nr_pages_per_cpu) {
 631                 fprintf(stderr, "invalid MiB\n");
 632                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 633         }
 634         bounces = atoi(argv[2]);
 635         if (bounces <= 0) {
 636                 fprintf(stderr, "invalid bounces\n");
 637                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 638         }
 639         nr_pages = nr_pages_per_cpu * nr_cpus;
 640         printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
 641                nr_pages, nr_pages_per_cpu);
 642         return userfaultfd_stress();
 643 }