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 #ifdef __NR_userfaultfd
  70
  71 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
  72
  73 #define BOUNCE_RANDOM           (1<<0)
  74 #define BOUNCE_RACINGFAULTS     (1<<1)
  75 #define BOUNCE_VERIFY           (1<<2)
  76 #define BOUNCE_POLL             (1<<3)
  77 static int bounces;
  78
  79 static unsigned long long *count_verify;
  80 static int uffd, finished, *pipefd;
  81 static char *area_src, *area_dst;
  82 static char *zeropage;
  83 pthread_attr_t attr;
  84
  85 /* pthread_mutex_t starts at page offset 0 */
  86 #define area_mutex(___area, ___nr)                                      \
  87         ((pthread_mutex_t *) ((___area) + (___nr)*page_size))
  88 /*
  89  * count is placed in the page after pthread_mutex_t naturally aligned
  90  * to avoid non alignment faults on non-x86 archs.
  91  */
  92 #define area_count(___area, ___nr)                                      \
  93         ((volatile unsigned long long *) ((unsigned long)               \
  94                                  ((___area) + (___nr)*page_size +       \
  95                                   sizeof(pthread_mutex_t) +             \
  96                                   sizeof(unsigned long long) - 1) &     \
  97                                  ~(unsigned long)(sizeof(unsigned long long) \
  98                                                   -  1)))
  99
 100 static int my_bcmp(char *str1, char *str2, size_t n)
 101 {
 102         unsigned long i;
 103         for (i = 0; i < n; i++)
 104                 if (str1[i] != str2[i])
 105                         return 1;
 106         return 0;
 107 }
 108
 109 static void *locking_thread(void *arg)
 110 {
 111         unsigned long cpu = (unsigned long) arg;
 112         struct random_data rand;
 113         unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
 114         int32_t rand_nr;
 115         unsigned long long count;
 116         char randstate[64];
 117         unsigned int seed;
 118         time_t start;
 119
 120         if (bounces & BOUNCE_RANDOM) {
 121                 seed = (unsigned int) time(NULL) - bounces;
 122                 if (!(bounces & BOUNCE_RACINGFAULTS))
 123                         seed += cpu;
 124                 bzero(&rand, sizeof(rand));
 125                 bzero(&randstate, sizeof(randstate));
 126                 if (initstate_r(seed, randstate, sizeof(randstate), &rand))
 127                         fprintf(stderr, "srandom_r error\n"), exit(1);
 128         } else {
 129                 page_nr = -bounces;
 130                 if (!(bounces & BOUNCE_RACINGFAULTS))
 131                         page_nr += cpu * nr_pages_per_cpu;
 132         }
 133
 134         while (!finished) {
 135                 if (bounces & BOUNCE_RANDOM) {
 136                         if (random_r(&rand, &rand_nr))
 137                                 fprintf(stderr, "random_r 1 error\n"), exit(1);
 138                         page_nr = rand_nr;
 139                         if (sizeof(page_nr) > sizeof(rand_nr)) {
 140                                 if (random_r(&rand, &rand_nr))
 141                                         fprintf(stderr, "random_r 2 error\n"), exit(1);
 142                                 page_nr |= (((unsigned long) rand_nr) << 16) <<
 143                                            16;
 144                         }
 145                 } else
 146                         page_nr += 1;
 147                 page_nr %= nr_pages;
 148
 149                 start = time(NULL);
 150                 if (bounces & BOUNCE_VERIFY) {
 151                         count = *area_count(area_dst, page_nr);
 152                         if (!count)
 153                                 fprintf(stderr,
 154                                         "page_nr %lu wrong count %Lu %Lu\n",
 155                                         page_nr, count,
 156                                         count_verify[page_nr]), exit(1);
 157
 158
 159                         /*
 160                          * We can't use bcmp (or memcmp) because that
 161                          * returns 0 erroneously if the memory is
 162                          * changing under it (even if the end of the
 163                          * page is never changing and always
 164                          * different).
 165                          */
 166 #if 1
 167                         if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
 168                                      page_size))
 169                                 fprintf(stderr,
 170                                         "my_bcmp page_nr %lu wrong count %Lu %Lu\n",
 171                                         page_nr, count,
 172                                         count_verify[page_nr]), exit(1);
 173 #else
 174                         unsigned long loops;
 175
 176                         loops = 0;
 177                         /* uncomment the below line to test with mutex */
 178                         /* pthread_mutex_lock(area_mutex(area_dst, page_nr)); */
 179                         while (!bcmp(area_dst + page_nr * page_size, zeropage,
 180                                      page_size)) {
 181                                 loops += 1;
 182                                 if (loops > 10)
 183                                         break;
 184                         }
 185                         /* uncomment below line to test with mutex */
 186                         /* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
 187                         if (loops) {
 188                                 fprintf(stderr,
 189                                         "page_nr %lu all zero thread %lu %p %lu\n",
 190                                         page_nr, cpu, area_dst + page_nr * page_size,
 191                                         loops);
 192                                 if (loops > 10)
 193                                         exit(1);
 194                         }
 195 #endif
 196                 }
 197
 198                 pthread_mutex_lock(area_mutex(area_dst, page_nr));
 199                 count = *area_count(area_dst, page_nr);
 200                 if (count != count_verify[page_nr]) {
 201                         fprintf(stderr,
 202                                 "page_nr %lu memory corruption %Lu %Lu\n",
 203                                 page_nr, count,
 204                                 count_verify[page_nr]), exit(1);
 205                 }
 206                 count++;
 207                 *area_count(area_dst, page_nr) = count_verify[page_nr] = count;
 208                 pthread_mutex_unlock(area_mutex(area_dst, page_nr));
 209
 210                 if (time(NULL) - start > 1)
 211                         fprintf(stderr,
 212                                 "userfault too slow %ld "
 213                                 "possible false positive with overcommit\n",
 214                                 time(NULL) - start);
 215         }
 216
 217         return NULL;
 218 }
 219
 220 static int copy_page(unsigned long offset)
 221 {
 222         struct uffdio_copy uffdio_copy;
 223
 224         if (offset >= nr_pages * page_size)
 225                 fprintf(stderr, "unexpected offset %lu\n",
 226                         offset), exit(1);
 227         uffdio_copy.dst = (unsigned long) area_dst + offset;
 228         uffdio_copy.src = (unsigned long) area_src + offset;
 229         uffdio_copy.len = page_size;
 230         uffdio_copy.mode = 0;
 231         uffdio_copy.copy = 0;
 232         if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy)) {
 233                 /* real retval in ufdio_copy.copy */
 234                 if (uffdio_copy.copy != -EEXIST)
 235                         fprintf(stderr, "UFFDIO_COPY error %Ld\n",
 236                                 uffdio_copy.copy), exit(1);
 237         } else if (uffdio_copy.copy != page_size) {
 238                 fprintf(stderr, "UFFDIO_COPY unexpected copy %Ld\n",
 239                         uffdio_copy.copy), exit(1);
 240         } else
 241                 return 1;
 242         return 0;
 243 }
 244
 245 static void *uffd_poll_thread(void *arg)
 246 {
 247         unsigned long cpu = (unsigned long) arg;
 248         struct pollfd pollfd[2];
 249         struct uffd_msg msg;
 250         int ret;
 251         unsigned long offset;
 252         char tmp_chr;
 253         unsigned long userfaults = 0;
 254
 255         pollfd[0].fd = uffd;
 256         pollfd[0].events = POLLIN;
 257         pollfd[1].fd = pipefd[cpu*2];
 258         pollfd[1].events = POLLIN;
 259
 260         for (;;) {
 261                 ret = poll(pollfd, 2, -1);
 262                 if (!ret)
 263                         fprintf(stderr, "poll error %d\n", ret), exit(1);
 264                 if (ret < 0)
 265                         perror("poll"), exit(1);
 266                 if (pollfd[1].revents & POLLIN) {
 267                         if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
 268                                 fprintf(stderr, "read pipefd error\n"),
 269                                         exit(1);
 270                         break;
 271                 }
 272                 if (!(pollfd[0].revents & POLLIN))
 273                         fprintf(stderr, "pollfd[0].revents %d\n",
 274                                 pollfd[0].revents), exit(1);
 275                 ret = read(uffd, &msg, sizeof(msg));
 276                 if (ret < 0) {
 277                         if (errno == EAGAIN)
 278                                 continue;
 279                         perror("nonblocking read error"), exit(1);
 280                 }
 281                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 282                         fprintf(stderr, "unexpected msg event %u\n",
 283                                 msg.event), exit(1);
 284                 if (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 285                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 286                 offset = (char *)(unsigned long)msg.arg.pagefault.address -
 287                          area_dst;
 288                 offset &= ~(page_size-1);
 289                 if (copy_page(offset))
 290                         userfaults++;
 291         }
 292         return (void *)userfaults;
 293 }
 294
 295 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
 296
 297 static void *uffd_read_thread(void *arg)
 298 {
 299         unsigned long *this_cpu_userfaults;
 300         struct uffd_msg msg;
 301         unsigned long offset;
 302         int ret;
 303
 304         this_cpu_userfaults = (unsigned long *) arg;
 305         *this_cpu_userfaults = 0;
 306
 307         pthread_mutex_unlock(&uffd_read_mutex);
 308         /* from here cancellation is ok */
 309
 310         for (;;) {
 311                 ret = read(uffd, &msg, sizeof(msg));
 312                 if (ret != sizeof(msg)) {
 313                         if (ret < 0)
 314                                 perror("blocking read error"), exit(1);
 315                         else
 316                                 fprintf(stderr, "short read\n"), exit(1);
 317                 }
 318                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 319                         fprintf(stderr, "unexpected msg event %u\n",
 320                                 msg.event), exit(1);
 321                 if (bounces & BOUNCE_VERIFY &&
 322                     msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 323                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 324                 offset = (char *)(unsigned long)msg.arg.pagefault.address -
 325                          area_dst;
 326                 offset &= ~(page_size-1);
 327                 if (copy_page(offset))
 328                         (*this_cpu_userfaults)++;
 329         }
 330         return (void *)NULL;
 331 }
 332
 333 static void *background_thread(void *arg)
 334 {
 335         unsigned long cpu = (unsigned long) arg;
 336         unsigned long page_nr;
 337
 338         for (page_nr = cpu * nr_pages_per_cpu;
 339              page_nr < (cpu+1) * nr_pages_per_cpu;
 340              page_nr++)
 341                 copy_page(page_nr * page_size);
 342
 343         return NULL;
 344 }
 345
 346 static int stress(unsigned long *userfaults)
 347 {
 348         unsigned long cpu;
 349         pthread_t locking_threads[nr_cpus];
 350         pthread_t uffd_threads[nr_cpus];
 351         pthread_t background_threads[nr_cpus];
 352         void **_userfaults = (void **) userfaults;
 353
 354         finished = 0;
 355         for (cpu = 0; cpu < nr_cpus; cpu++) {
 356                 if (pthread_create(&locking_threads[cpu], &attr,
 357                                    locking_thread, (void *)cpu))
 358                         return 1;
 359                 if (bounces & BOUNCE_POLL) {
 360                         if (pthread_create(&uffd_threads[cpu], &attr,
 361                                            uffd_poll_thread, (void *)cpu))
 362                                 return 1;
 363                 } else {
 364                         if (pthread_create(&uffd_threads[cpu], &attr,
 365                                            uffd_read_thread,
 366                                            &_userfaults[cpu]))
 367                                 return 1;
 368                         pthread_mutex_lock(&uffd_read_mutex);
 369                 }
 370                 if (pthread_create(&background_threads[cpu], &attr,
 371                                    background_thread, (void *)cpu))
 372                         return 1;
 373         }
 374         for (cpu = 0; cpu < nr_cpus; cpu++)
 375                 if (pthread_join(background_threads[cpu], NULL))
 376                         return 1;
 377
 378         /*
 379          * Be strict and immediately zap area_src, the whole area has
 380          * been transferred already by the background treads. The
 381          * area_src could then be faulted in in a racy way by still
 382          * running uffdio_threads reading zeropages after we zapped
 383          * area_src (but they're guaranteed to get -EEXIST from
 384          * UFFDIO_COPY without writing zero pages into area_dst
 385          * because the background threads already completed).
 386          */
 387         if (madvise(area_src, nr_pages * page_size, MADV_DONTNEED)) {
 388                 perror("madvise");
 389                 return 1;
 390         }
 391
 392         for (cpu = 0; cpu < nr_cpus; cpu++) {
 393                 char c;
 394                 if (bounces & BOUNCE_POLL) {
 395                         if (write(pipefd[cpu*2+1], &c, 1) != 1) {
 396                                 fprintf(stderr, "pipefd write error\n");
 397                                 return 1;
 398                         }
 399                         if (pthread_join(uffd_threads[cpu], &_userfaults[cpu]))
 400                                 return 1;
 401                 } else {
 402                         if (pthread_cancel(uffd_threads[cpu]))
 403                                 return 1;
 404                         if (pthread_join(uffd_threads[cpu], NULL))
 405                                 return 1;
 406                 }
 407         }
 408
 409         finished = 1;
 410         for (cpu = 0; cpu < nr_cpus; cpu++)
 411                 if (pthread_join(locking_threads[cpu], NULL))
 412                         return 1;
 413
 414         return 0;
 415 }
 416
 417 static int userfaultfd_stress(void)
 418 {
 419         void *area;
 420         char *tmp_area;
 421         unsigned long nr;
 422         struct uffdio_register uffdio_register;
 423         struct uffdio_api uffdio_api;
 424         unsigned long cpu;
 425         int uffd_flags;
 426         unsigned long userfaults[nr_cpus];
 427
 428         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 429                 fprintf(stderr, "out of memory\n");
 430                 return 1;
 431         }
 432         area_src = area;
 433         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 434                 fprintf(stderr, "out of memory\n");
 435                 return 1;
 436         }
 437         area_dst = area;
 438
 439         uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 440         if (uffd < 0) {
 441                 fprintf(stderr,
 442                         "userfaultfd syscall not available in this kernel\n");
 443                 return 1;
 444         }
 445         uffd_flags = fcntl(uffd, F_GETFD, NULL);
 446
 447         uffdio_api.api = UFFD_API;
 448         uffdio_api.features = 0;
 449         if (ioctl(uffd, UFFDIO_API, &uffdio_api)) {
 450                 fprintf(stderr, "UFFDIO_API\n");
 451                 return 1;
 452         }
 453         if (uffdio_api.api != UFFD_API) {
 454                 fprintf(stderr, "UFFDIO_API error %Lu\n", uffdio_api.api);
 455                 return 1;
 456         }
 457
 458         count_verify = malloc(nr_pages * sizeof(unsigned long long));
 459         if (!count_verify) {
 460                 perror("count_verify");
 461                 return 1;
 462         }
 463
 464         for (nr = 0; nr < nr_pages; nr++) {
 465                 *area_mutex(area_src, nr) = (pthread_mutex_t)
 466                         PTHREAD_MUTEX_INITIALIZER;
 467                 count_verify[nr] = *area_count(area_src, nr) = 1;
 468                 /*
 469                  * In the transition between 255 to 256, powerpc will
 470                  * read out of order in my_bcmp and see both bytes as
 471                  * zero, so leave a placeholder below always non-zero
 472                  * after the count, to avoid my_bcmp to trigger false
 473                  * positives.
 474                  */
 475                 *(area_count(area_src, nr) + 1) = 1;
 476         }
 477
 478         pipefd = malloc(sizeof(int) * nr_cpus * 2);
 479         if (!pipefd) {
 480                 perror("pipefd");
 481                 return 1;
 482         }
 483         for (cpu = 0; cpu < nr_cpus; cpu++) {
 484                 if (pipe2(&pipefd[cpu*2], O_CLOEXEC | O_NONBLOCK)) {
 485                         perror("pipe");
 486                         return 1;
 487                 }
 488         }
 489
 490         if (posix_memalign(&area, page_size, page_size)) {
 491                 fprintf(stderr, "out of memory\n");
 492                 return 1;
 493         }
 494         zeropage = area;
 495         bzero(zeropage, page_size);
 496
 497         pthread_mutex_lock(&uffd_read_mutex);
 498
 499         pthread_attr_init(&attr);
 500         pthread_attr_setstacksize(&attr, 16*1024*1024);
 501
 502         while (bounces--) {
 503                 unsigned long expected_ioctls;
 504
 505                 printf("bounces: %d, mode:", bounces);
 506                 if (bounces & BOUNCE_RANDOM)
 507                         printf(" rnd");
 508                 if (bounces & BOUNCE_RACINGFAULTS)
 509                         printf(" racing");
 510                 if (bounces & BOUNCE_VERIFY)
 511                         printf(" ver");
 512                 if (bounces & BOUNCE_POLL)
 513                         printf(" poll");
 514                 printf(", ");
 515                 fflush(stdout);
 516
 517                 if (bounces & BOUNCE_POLL)
 518                         fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 519                 else
 520                         fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
 521
 522                 /* register */
 523                 uffdio_register.range.start = (unsigned long) area_dst;
 524                 uffdio_register.range.len = nr_pages * page_size;
 525                 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
 526                 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
 527                         fprintf(stderr, "register failure\n");
 528                         return 1;
 529                 }
 530                 expected_ioctls = (1 << _UFFDIO_WAKE) |
 531                                   (1 << _UFFDIO_COPY) |
 532                                   (1 << _UFFDIO_ZEROPAGE);
 533                 if ((uffdio_register.ioctls & expected_ioctls) !=
 534                     expected_ioctls) {
 535                         fprintf(stderr,
 536                                 "unexpected missing ioctl for anon memory\n");
 537                         return 1;
 538                 }
 539
 540                 /*
 541                  * The madvise done previously isn't enough: some
 542                  * uffd_thread could have read userfaults (one of
 543                  * those already resolved by the background thread)
 544                  * and it may be in the process of calling
 545                  * UFFDIO_COPY. UFFDIO_COPY will read the zapped
 546                  * area_src and it would map a zero page in it (of
 547                  * course such a UFFDIO_COPY is perfectly safe as it'd
 548                  * return -EEXIST). The problem comes at the next
 549                  * bounce though: that racing UFFDIO_COPY would
 550                  * generate zeropages in the area_src, so invalidating
 551                  * the previous MADV_DONTNEED. Without this additional
 552                  * MADV_DONTNEED those zeropages leftovers in the
 553                  * area_src would lead to -EEXIST failure during the
 554                  * next bounce, effectively leaving a zeropage in the
 555                  * area_dst.
 556                  *
 557                  * Try to comment this out madvise to see the memory
 558                  * corruption being caught pretty quick.
 559                  *
 560                  * khugepaged is also inhibited to collapse THP after
 561                  * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
 562                  * required to MADV_DONTNEED here.
 563                  */
 564                 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
 565                         perror("madvise 2");
 566                         return 1;
 567                 }
 568
 569                 /* bounce pass */
 570                 if (stress(userfaults))
 571                         return 1;
 572
 573                 /* unregister */
 574                 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
 575                         fprintf(stderr, "register failure\n");
 576                         return 1;
 577                 }
 578
 579                 /* verification */
 580                 if (bounces & BOUNCE_VERIFY) {
 581                         for (nr = 0; nr < nr_pages; nr++) {
 582                                 if (my_bcmp(area_dst,
 583                                             area_dst + nr * page_size,
 584                                             sizeof(pthread_mutex_t))) {
 585                                         fprintf(stderr,
 586                                                 "error mutex 2 %lu\n",
 587                                                 nr);
 588                                         bounces = 0;
 589                                 }
 590                                 if (*area_count(area_dst, nr) != count_verify[nr]) {
 591                                         fprintf(stderr,
 592                                                 "error area_count %Lu %Lu %lu\n",
 593                                                 *area_count(area_src, nr),
 594                                                 count_verify[nr],
 595                                                 nr);
 596                                         bounces = 0;
 597                                 }
 598                         }
 599                 }
 600
 601                 /* prepare next bounce */
 602                 tmp_area = area_src;
 603                 area_src = area_dst;
 604                 area_dst = tmp_area;
 605
 606                 printf("userfaults:");
 607                 for (cpu = 0; cpu < nr_cpus; cpu++)
 608                         printf(" %lu", userfaults[cpu]);
 609                 printf("\n");
 610         }
 611
 612         return 0;
 613 }
 614
 615 int main(int argc, char **argv)
 616 {
 617         if (argc < 3)
 618                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 619         nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
 620         page_size = sysconf(_SC_PAGE_SIZE);
 621         if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) * 2
 622             > page_size)
 623                 fprintf(stderr, "Impossible to run this test\n"), exit(2);
 624         nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
 625                 nr_cpus;
 626         if (!nr_pages_per_cpu) {
 627                 fprintf(stderr, "invalid MiB\n");
 628                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 629         }
 630         bounces = atoi(argv[2]);
 631         if (bounces <= 0) {
 632                 fprintf(stderr, "invalid bounces\n");
 633                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 634         }
 635         nr_pages = nr_pages_per_cpu * nr_cpus;
 636         printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
 637                nr_pages, nr_pages_per_cpu);
 638         return userfaultfd_stress();
 639 }
 640
 641 #else /* __NR_userfaultfd */
 642
 643 #warning "missing __NR_userfaultfd definition"
 644
 645 int main(void)
 646 {
 647         printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
 648         return 0;
 649 }
 650
 651 #endif /* __NR_userfaultfd */