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Linux/tools/testing/selftests/vm/userfaultfd.c

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  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, err;
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         err = 0;
503         while (bounces--) {
504                 unsigned long expected_ioctls;
505 
506                 printf("bounces: %d, mode:", bounces);
507                 if (bounces & BOUNCE_RANDOM)
508                         printf(" rnd");
509                 if (bounces & BOUNCE_RACINGFAULTS)
510                         printf(" racing");
511                 if (bounces & BOUNCE_VERIFY)
512                         printf(" ver");
513                 if (bounces & BOUNCE_POLL)
514                         printf(" poll");
515                 printf(", ");
516                 fflush(stdout);
517 
518                 if (bounces & BOUNCE_POLL)
519                         fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
520                 else
521                         fcntl(uffd, F_SETFL, uffd_flags & ~O_NONBLOCK);
522 
523                 /* register */
524                 uffdio_register.range.start = (unsigned long) area_dst;
525                 uffdio_register.range.len = nr_pages * page_size;
526                 uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
527                 if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
528                         fprintf(stderr, "register failure\n");
529                         return 1;
530                 }
531                 expected_ioctls = (1 << _UFFDIO_WAKE) |
532                                   (1 << _UFFDIO_COPY) |
533                                   (1 << _UFFDIO_ZEROPAGE);
534                 if ((uffdio_register.ioctls & expected_ioctls) !=
535                     expected_ioctls) {
536                         fprintf(stderr,
537                                 "unexpected missing ioctl for anon memory\n");
538                         return 1;
539                 }
540 
541                 /*
542                  * The madvise done previously isn't enough: some
543                  * uffd_thread could have read userfaults (one of
544                  * those already resolved by the background thread)
545                  * and it may be in the process of calling
546                  * UFFDIO_COPY. UFFDIO_COPY will read the zapped
547                  * area_src and it would map a zero page in it (of
548                  * course such a UFFDIO_COPY is perfectly safe as it'd
549                  * return -EEXIST). The problem comes at the next
550                  * bounce though: that racing UFFDIO_COPY would
551                  * generate zeropages in the area_src, so invalidating
552                  * the previous MADV_DONTNEED. Without this additional
553                  * MADV_DONTNEED those zeropages leftovers in the
554                  * area_src would lead to -EEXIST failure during the
555                  * next bounce, effectively leaving a zeropage in the
556                  * area_dst.
557                  *
558                  * Try to comment this out madvise to see the memory
559                  * corruption being caught pretty quick.
560                  *
561                  * khugepaged is also inhibited to collapse THP after
562                  * MADV_DONTNEED only after the UFFDIO_REGISTER, so it's
563                  * required to MADV_DONTNEED here.
564                  */
565                 if (madvise(area_dst, nr_pages * page_size, MADV_DONTNEED)) {
566                         perror("madvise 2");
567                         return 1;
568                 }
569 
570                 /* bounce pass */
571                 if (stress(userfaults))
572                         return 1;
573 
574                 /* unregister */
575                 if (ioctl(uffd, UFFDIO_UNREGISTER, &uffdio_register.range)) {
576                         fprintf(stderr, "register failure\n");
577                         return 1;
578                 }
579 
580                 /* verification */
581                 if (bounces & BOUNCE_VERIFY) {
582                         for (nr = 0; nr < nr_pages; nr++) {
583                                 if (*area_count(area_dst, nr) != count_verify[nr]) {
584                                         fprintf(stderr,
585                                                 "error area_count %Lu %Lu %lu\n",
586                                                 *area_count(area_src, nr),
587                                                 count_verify[nr],
588                                                 nr);
589                                         err = 1;
590                                         bounces = 0;
591                                 }
592                         }
593                 }
594 
595                 /* prepare next bounce */
596                 tmp_area = area_src;
597                 area_src = area_dst;
598                 area_dst = tmp_area;
599 
600                 printf("userfaults:");
601                 for (cpu = 0; cpu < nr_cpus; cpu++)
602                         printf(" %lu", userfaults[cpu]);
603                 printf("\n");
604         }
605 
606         return err;
607 }
608 
609 int main(int argc, char **argv)
610 {
611         if (argc < 3)
612                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
613         nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
614         page_size = sysconf(_SC_PAGE_SIZE);
615         if ((unsigned long) area_count(NULL, 0) + sizeof(unsigned long long) * 2
616             > page_size)
617                 fprintf(stderr, "Impossible to run this test\n"), exit(2);
618         nr_pages_per_cpu = atol(argv[1]) * 1024*1024 / page_size /
619                 nr_cpus;
620         if (!nr_pages_per_cpu) {
621                 fprintf(stderr, "invalid MiB\n");
622                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
623         }
624         bounces = atoi(argv[2]);
625         if (bounces <= 0) {
626                 fprintf(stderr, "invalid bounces\n");
627                 fprintf(stderr, "Usage: <MiB> <bounces>\n"), exit(1);
628         }
629         nr_pages = nr_pages_per_cpu * nr_cpus;
630         printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
631                nr_pages, nr_pages_per_cpu);
632         return userfaultfd_stress();
633 }
634 
635 #else /* __NR_userfaultfd */
636 
637 #warning "missing __NR_userfaultfd definition"
638 
639 int main(void)
640 {
641         printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
642         return 0;
643 }
644 
645 #endif /* __NR_userfaultfd */
646 

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