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 359
  73 #elif defined(__powewrpc__)
  74 #define __NR_userfaultfd 364
  75 #else
  76 #error "missing __NR_userfaultfd definition"
  77 #endif
  78
  79 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
  80
  81 #define BOUNCE_RANDOM           (1<<0)
  82 #define BOUNCE_RACINGFAULTS     (1<<1)
  83 #define BOUNCE_VERIFY           (1<<2)
  84 #define BOUNCE_POLL             (1<<3)
  85 static int bounces;
  86
  87 static unsigned long long *count_verify;
  88 static int uffd, finished, *pipefd;
  89 static char *area_src, *area_dst;
  90 static char *zeropage;
  91 pthread_attr_t attr;
  92
  93 /* pthread_mutex_t starts at page offset 0 */
  94 #define area_mutex(___area, ___nr)                                      \
  95         ((pthread_mutex_t *) ((___area) + (___nr)*page_size))
  96 /*
  97  * count is placed in the page after pthread_mutex_t naturally aligned
  98  * to avoid non alignment faults on non-x86 archs.
  99  */
 100 #define area_count(___area, ___nr)                                      \
 101         ((volatile unsigned long long *) ((unsigned long)               \
 102                                  ((___area) + (___nr)*page_size +       \
 103                                   sizeof(pthread_mutex_t) +             \
 104                                   sizeof(unsigned long long) - 1) &     \
 105                                  ~(unsigned long)(sizeof(unsigned long long) \
 106                                                   -  1)))
 107
 108 static int my_bcmp(char *str1, char *str2, size_t n)
 109 {
 110         unsigned long i;
 111         for (i = 0; i < n; i++)
 112                 if (str1[i] != str2[i])
 113                         return 1;
 114         return 0;
 115 }
 116
 117 static void *locking_thread(void *arg)
 118 {
 119         unsigned long cpu = (unsigned long) arg;
 120         struct random_data rand;
 121         unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
 122         int32_t rand_nr;
 123         unsigned long long count;
 124         char randstate[64];
 125         unsigned int seed;
 126         time_t start;
 127
 128         if (bounces & BOUNCE_RANDOM) {
 129                 seed = (unsigned int) time(NULL) - bounces;
 130                 if (!(bounces & BOUNCE_RACINGFAULTS))
 131                         seed += cpu;
 132                 bzero(&rand, sizeof(rand));
 133                 bzero(&randstate, sizeof(randstate));
 134                 if (initstate_r(seed, randstate, sizeof(randstate), &rand))
 135                         fprintf(stderr, "srandom_r error\n"), exit(1);
 136         } else {
 137                 page_nr = -bounces;
 138                 if (!(bounces & BOUNCE_RACINGFAULTS))
 139                         page_nr += cpu * nr_pages_per_cpu;
 140         }
 141
 142         while (!finished) {
 143                 if (bounces & BOUNCE_RANDOM) {
 144                         if (random_r(&rand, &rand_nr))
 145                                 fprintf(stderr, "random_r 1 error\n"), exit(1);
 146                         page_nr = rand_nr;
 147                         if (sizeof(page_nr) > sizeof(rand_nr)) {
 148                                 if (random_r(&rand, &rand_nr))
 149                                         fprintf(stderr, "random_r 2 error\n"), exit(1);
 150                                 page_nr |= ((unsigned long) rand_nr) << 32;
 151                         }
 152                 } else
 153                         page_nr += 1;
 154                 page_nr %= nr_pages;
 155
 156                 start = time(NULL);
 157                 if (bounces & BOUNCE_VERIFY) {
 158                         count = *area_count(area_dst, page_nr);
 159                         if (!count)
 160                                 fprintf(stderr,
 161                                         "page_nr %lu wrong count %Lu %Lu\n",
 162                                         page_nr, count,
 163                                         count_verify[page_nr]), exit(1);
 164
 165
 166                         /*
 167                          * We can't use bcmp (or memcmp) because that
 168                          * returns 0 erroneously if the memory is
 169                          * changing under it (even if the end of the
 170                          * page is never changing and always
 171                          * different).
 172                          */
 173 #if 1
 174                         if (!my_bcmp(area_dst + page_nr * page_size, zeropage,
 175                                      page_size))
 176                                 fprintf(stderr,
 177                                         "my_bcmp page_nr %lu wrong count %Lu %Lu\n",
 178                                         page_nr, count,
 179                                         count_verify[page_nr]), exit(1);
 180 #else
 181                         unsigned long loops;
 182
 183                         loops = 0;
 184                         /* uncomment the below line to test with mutex */
 185                         /* pthread_mutex_lock(area_mutex(area_dst, page_nr)); */
 186                         while (!bcmp(area_dst + page_nr * page_size, zeropage,
 187                                      page_size)) {
 188                                 loops += 1;
 189                                 if (loops > 10)
 190                                         break;
 191                         }
 192                         /* uncomment below line to test with mutex */
 193                         /* pthread_mutex_unlock(area_mutex(area_dst, page_nr)); */
 194                         if (loops) {
 195                                 fprintf(stderr,
 196                                         "page_nr %lu all zero thread %lu %p %lu\n",
 197                                         page_nr, cpu, area_dst + page_nr * page_size,
 198                                         loops);
 199                                 if (loops > 10)
 200                                         exit(1);
 201                         }
 202 #endif
 203                 }
 204
 205                 pthread_mutex_lock(area_mutex(area_dst, page_nr));
 206                 count = *area_count(area_dst, page_nr);
 207                 if (count != count_verify[page_nr]) {
 208                         fprintf(stderr,
 209                                 "page_nr %lu memory corruption %Lu %Lu\n",
 210                                 page_nr, count,
 211                                 count_verify[page_nr]), exit(1);
 212                 }
 213                 count++;
 214                 *area_count(area_dst, page_nr) = count_verify[page_nr] = count;
 215                 pthread_mutex_unlock(area_mutex(area_dst, page_nr));
 216
 217                 if (time(NULL) - start > 1)
 218                         fprintf(stderr,
 219                                 "userfault too slow %ld "
 220                                 "possible false positive with overcommit\n",
 221                                 time(NULL) - start);
 222         }
 223
 224         return NULL;
 225 }
 226
 227 static int copy_page(unsigned long offset)
 228 {
 229         struct uffdio_copy uffdio_copy;
 230
 231         if (offset >= nr_pages * page_size)
 232                 fprintf(stderr, "unexpected offset %lu\n",
 233                         offset), exit(1);
 234         uffdio_copy.dst = (unsigned long) area_dst + offset;
 235         uffdio_copy.src = (unsigned long) area_src + offset;
 236         uffdio_copy.len = page_size;
 237         uffdio_copy.mode = 0;
 238         uffdio_copy.copy = 0;
 239         if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy)) {
 240                 /* real retval in ufdio_copy.copy */
 241                 if (uffdio_copy.copy != -EEXIST)
 242                         fprintf(stderr, "UFFDIO_COPY error %Ld\n",
 243                                 uffdio_copy.copy), exit(1);
 244         } else if (uffdio_copy.copy != page_size) {
 245                 fprintf(stderr, "UFFDIO_COPY unexpected copy %Ld\n",
 246                         uffdio_copy.copy), exit(1);
 247         } else
 248                 return 1;
 249         return 0;
 250 }
 251
 252 static void *uffd_poll_thread(void *arg)
 253 {
 254         unsigned long cpu = (unsigned long) arg;
 255         struct pollfd pollfd[2];
 256         struct uffd_msg msg;
 257         int ret;
 258         unsigned long offset;
 259         char tmp_chr;
 260         unsigned long userfaults = 0;
 261
 262         pollfd[0].fd = uffd;
 263         pollfd[0].events = POLLIN;
 264         pollfd[1].fd = pipefd[cpu*2];
 265         pollfd[1].events = POLLIN;
 266
 267         for (;;) {
 268                 ret = poll(pollfd, 2, -1);
 269                 if (!ret)
 270                         fprintf(stderr, "poll error %d\n", ret), exit(1);
 271                 if (ret < 0)
 272                         perror("poll"), exit(1);
 273                 if (pollfd[1].revents & POLLIN) {
 274                         if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
 275                                 fprintf(stderr, "read pipefd error\n"),
 276                                         exit(1);
 277                         break;
 278                 }
 279                 if (!(pollfd[0].revents & POLLIN))
 280                         fprintf(stderr, "pollfd[0].revents %d\n",
 281                                 pollfd[0].revents), exit(1);
 282                 ret = read(uffd, &msg, sizeof(msg));
 283                 if (ret < 0) {
 284                         if (errno == EAGAIN)
 285                                 continue;
 286                         perror("nonblocking read error"), exit(1);
 287                 }
 288                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 289                         fprintf(stderr, "unexpected msg event %u\n",
 290                                 msg.event), exit(1);
 291                 if (msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 292                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 293                 offset = (char *)msg.arg.pagefault.address - area_dst;
 294                 offset &= ~(page_size-1);
 295                 if (copy_page(offset))
 296                         userfaults++;
 297         }
 298         return (void *)userfaults;
 299 }
 300
 301 pthread_mutex_t uffd_read_mutex = PTHREAD_MUTEX_INITIALIZER;
 302
 303 static void *uffd_read_thread(void *arg)
 304 {
 305         unsigned long *this_cpu_userfaults;
 306         struct uffd_msg msg;
 307         unsigned long offset;
 308         int ret;
 309
 310         this_cpu_userfaults = (unsigned long *) arg;
 311         *this_cpu_userfaults = 0;
 312
 313         pthread_mutex_unlock(&uffd_read_mutex);
 314         /* from here cancellation is ok */
 315
 316         for (;;) {
 317                 ret = read(uffd, &msg, sizeof(msg));
 318                 if (ret != sizeof(msg)) {
 319                         if (ret < 0)
 320                                 perror("blocking read error"), exit(1);
 321                         else
 322                                 fprintf(stderr, "short read\n"), exit(1);
 323                 }
 324                 if (msg.event != UFFD_EVENT_PAGEFAULT)
 325                         fprintf(stderr, "unexpected msg event %u\n",
 326                                 msg.event), exit(1);
 327                 if (bounces & BOUNCE_VERIFY &&
 328                     msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
 329                         fprintf(stderr, "unexpected write fault\n"), exit(1);
 330                 offset = (char *)msg.arg.pagefault.address - area_dst;
 331                 offset &= ~(page_size-1);
 332                 if (copy_page(offset))
 333                         (*this_cpu_userfaults)++;
 334         }
 335         return (void *)NULL;
 336 }
 337
 338 static void *background_thread(void *arg)
 339 {
 340         unsigned long cpu = (unsigned long) arg;
 341         unsigned long page_nr;
 342
 343         for (page_nr = cpu * nr_pages_per_cpu;
 344              page_nr < (cpu+1) * nr_pages_per_cpu;
 345              page_nr++)
 346                 copy_page(page_nr * page_size);
 347
 348         return NULL;
 349 }
 350
 351 static int stress(unsigned long *userfaults)
 352 {
 353         unsigned long cpu;
 354         pthread_t locking_threads[nr_cpus];
 355         pthread_t uffd_threads[nr_cpus];
 356         pthread_t background_threads[nr_cpus];
 357         void **_userfaults = (void **) userfaults;
 358
 359         finished = 0;
 360         for (cpu = 0; cpu < nr_cpus; cpu++) {
 361                 if (pthread_create(&locking_threads[cpu], &attr,
 362                                    locking_thread, (void *)cpu))
 363                         return 1;
 364                 if (bounces & BOUNCE_POLL) {
 365                         if (pthread_create(&uffd_threads[cpu], &attr,
 366                                            uffd_poll_thread, (void *)cpu))
 367                                 return 1;
 368                 } else {
 369                         if (pthread_create(&uffd_threads[cpu], &attr,
 370                                            uffd_read_thread,
 371                                            &_userfaults[cpu]))
 372                                 return 1;
 373                         pthread_mutex_lock(&uffd_read_mutex);
 374                 }
 375                 if (pthread_create(&background_threads[cpu], &attr,
 376                                    background_thread, (void *)cpu))
 377                         return 1;
 378         }
 379         for (cpu = 0; cpu < nr_cpus; cpu++)
 380                 if (pthread_join(background_threads[cpu], NULL))
 381                         return 1;
 382
 383         /*
 384          * Be strict and immediately zap area_src, the whole area has
 385          * been transferred already by the background treads. The
 386          * area_src could then be faulted in in a racy way by still
 387          * running uffdio_threads reading zeropages after we zapped
 388          * area_src (but they're guaranteed to get -EEXIST from
 389          * UFFDIO_COPY without writing zero pages into area_dst
 390          * because the background threads already completed).
 391          */
 392         if (madvise(area_src, nr_pages * page_size, MADV_DONTNEED)) {
 393                 perror("madvise");
 394                 return 1;
 395         }
 396
 397         for (cpu = 0; cpu < nr_cpus; cpu++) {
 398                 char c;
 399                 if (bounces & BOUNCE_POLL) {
 400                         if (write(pipefd[cpu*2+1], &c, 1) != 1) {
 401                                 fprintf(stderr, "pipefd write error\n");
 402                                 return 1;
 403                         }
 404                         if (pthread_join(uffd_threads[cpu], &_userfaults[cpu]))
 405                                 return 1;
 406                 } else {
 407                         if (pthread_cancel(uffd_threads[cpu]))
 408                                 return 1;
 409                         if (pthread_join(uffd_threads[cpu], NULL))
 410                                 return 1;
 411                 }
 412         }
 413
 414         finished = 1;
 415         for (cpu = 0; cpu < nr_cpus; cpu++)
 416                 if (pthread_join(locking_threads[cpu], NULL))
 417                         return 1;
 418
 419         return 0;
 420 }
 421
 422 static int userfaultfd_stress(void)
 423 {
 424         void *area;
 425         char *tmp_area;
 426         unsigned long nr;
 427         struct uffdio_register uffdio_register;
 428         struct uffdio_api uffdio_api;
 429         unsigned long cpu;
 430         int uffd_flags;
 431         unsigned long userfaults[nr_cpus];
 432
 433         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 434                 fprintf(stderr, "out of memory\n");
 435                 return 1;
 436         }
 437         area_src = area;
 438         if (posix_memalign(&area, page_size, nr_pages * page_size)) {
 439                 fprintf(stderr, "out of memory\n");
 440                 return 1;
 441         }
 442         area_dst = area;
 443
 444         uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 445         if (uffd < 0) {
 446                 fprintf(stderr,
 447                         "userfaultfd syscall not available in this kernel\n");
 448                 return 1;
 449         }
 450         uffd_flags = fcntl(uffd, F_GETFD, NULL);
 451
 452         uffdio_api.api = UFFD_API;
 453         uffdio_api.features = 0;
 454         if (ioctl(uffd, UFFDIO_API, &uffdio_api)) {
 455                 fprintf(stderr, "UFFDIO_API\n");
 456                 return 1;
 457         }
 458         if (uffdio_api.api != UFFD_API) {
 459                 fprintf(stderr, "UFFDIO_API error %Lu\n", uffdio_api.api);
 460                 return 1;
 461         }
 462
 463         count_verify = malloc(nr_pages * sizeof(unsigned long long));
 464         if (!count_verify) {
 465                 perror("count_verify");
 466                 return 1;
 467         }
 468
 469         for (nr = 0; nr < nr_pages; nr++) {
 470                 *area_mutex(area_src, nr) = (pthread_mutex_t)
 471                         PTHREAD_MUTEX_INITIALIZER;
 472                 count_verify[nr] = *area_count(area_src, nr) = 1;
 473         }
 474
 475         pipefd = malloc(sizeof(int) * nr_cpus * 2);
 476         if (!pipefd) {
 477                 perror("pipefd");
 478                 return 1;
 479         }
 480         for (cpu = 0; cpu < nr_cpus; cpu++) {
 481                 if (pipe2(&pipefd[cpu*2], O_CLOEXEC | O_NONBLOCK)) {
 482                         perror("pipe");
 483                         return 1;
 484                 }
 485         }
 486
 487         if (posix_memalign(&area, page_size, page_size)) {
 488                 fprintf(stderr, "out of memory\n");
 489                 return 1;
 490         }
 491         zeropage = area;
 492         bzero(zeropage, page_size);
 493
 494         pthread_mutex_lock(&uffd_read_mutex);
 495
 496         pthread_attr_init(&attr);
 497         pthread_attr_setstacksize(&attr, 16*1024*1024);
 498
 499         while (bounces--) {
 500                 unsigned long expected_ioctls;
 501
 502                 printf("bounces: %d, mode:", bounces);
 503                 if (bounces & BOUNCE_RANDOM)
 504                         printf(" rnd");
 505                 if (bounces & BOUNCE_RACINGFAULTS)
 506                         printf(" racing");
 507                 if (bounces & BOUNCE_VERIFY)
 508                         printf(" ver");
 509                 if (bounces & BOUNCE_POLL)
 510                         printf(" poll");
 511                 printf(", ");
 512                 fflush(stdout);
 513
 514                 if (bounces & BOUNCE_POLL)
 515                         fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
 516                 else
 517                         fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
 518
 519                 /* register */
 520                 uffdio_register.range.start = (unsigned long) area_dst;
 521                 uffdio_register.range.len = nr_pages * page_size;
 522                 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
 523                 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
 524                         fprintf(stderr, "register failure\n");
 525                         return 1;
 526                 }
 527                 expected_ioctls = (1 << _UFFDIO_WAKE) |
 528                                   (1 << _UFFDIO_COPY) |
 529                                   (1 << _UFFDIO_ZEROPAGE);
 530                 if ((uffdio_register.ioctls & expected_ioctls) !=
 531                     expected_ioctls) {
 532                         fprintf(stderr,
 533                                 "unexpected missing ioctl for anon memory\n");
 534                         return 1;
 535                 }
 536
 537                 /*
 538                  * The madvise done previously isn't enough: some
 539                  * uffd_thread could have read userfaults (one of
 540                  * those already resolved by the background thread)
 541                  * and it may be in the process of calling
 542                  * UFFDIO_COPY. UFFDIO_COPY will read the zapped
 543                  * area_src and it would map a zero page in it (of
 544                  * course such a UFFDIO_COPY is perfectly safe as it'd
 545                  * return -EEXIST). The problem comes at the next
 546                  * bounce though: that racing UFFDIO_COPY would
 547                  * generate zeropages in the area_src, so invalidating
 548                  * the previous MADV_DONTNEED. Without this additional
 549                  * MADV_DONTNEED those zeropages leftovers in the
 550                  * area_src would lead to -EEXIST failure during the
 551                  * next bounce, effectively leaving a zeropage in the
 552                  * area_dst.
 553                  *
 554                  * Try to comment this out madvise to see the memory
 555                  * corruption being caught pretty quick.
 556                  *
 557                  * khugepaged is also inhibited to collapse THP after
 558                  * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
 559                  * required to MADV_DONTNEED here.
 560                  */
 561                 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
 562                         perror("madvise 2");
 563                         return 1;
 564                 }
 565
 566                 /* bounce pass */
 567                 if (stress(userfaults))
 568                         return 1;
 569
 570                 /* unregister */
 571                 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
 572                         fprintf(stderr, "register failure\n");
 573                         return 1;
 574                 }
 575
 576                 /* verification */
 577                 if (bounces & BOUNCE_VERIFY) {
 578                         for (nr = 0; nr < nr_pages; nr++) {
 579                                 if (my_bcmp(area_dst,
 580                                             area_dst + nr * page_size,
 581                                             sizeof(pthread_mutex_t))) {
 582                                         fprintf(stderr,
 583                                                 "error mutex 2 %lu\n",
 584                                                 nr);
 585                                         bounces = 0;
 586                                 }
 587                                 if (*area_count(area_dst, nr) != count_verify[nr]) {
 588                                         fprintf(stderr,
 589                                                 "error area_count %Lu %Lu %lu\n",
 590                                                 *area_count(area_src, nr),
 591                                                 count_verify[nr],
 592                                                 nr);
 593                                         bounces = 0;
 594                                 }
 595                         }
 596                 }
 597
 598                 /* prepare next bounce */
 599                 tmp_area = area_src;
 600                 area_src = area_dst;
 601                 area_dst = tmp_area;
 602
 603                 printf("userfaults:");
 604                 for (cpu = 0; cpu < nr_cpus; cpu++)
 605                         printf(" %lu", userfaults[cpu]);
 606                 printf("\n");
 607         }
 608
 609         return 0;
 610 }
 611
 612 int main(int argc, char **argv)
 613 {
 614         if (argc < 3)
 615                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 616         nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
 617         page_size = sysconf(_SC_PAGE_SIZE);
 618         if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) >
 619             page_size)
 620                 fprintf(stderr, "Impossible to run this test\n"), exit(2);
 621         nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
 622                 nr_cpus;
 623         if (!nr_pages_per_cpu) {
 624                 fprintf(stderr, "invalid MiB\n");
 625                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 626         }
 627         bounces = atoi(argv[2]);
 628         if (bounces <= 0) {
 629                 fprintf(stderr, "invalid bounces\n");
 630                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
 631         }
 632         nr_pages = nr_pages_per_cpu * nr_cpus;
 633         printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
 634                nr_pages, nr_pages_per_cpu);
 635         return userfaultfd_stress();
 636 }