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