xref: /openbmc/qemu/migration/postcopy-ram.c (revision be3fc97a)
1 /*
2  * Postcopy migration for RAM
3  *
4  * Copyright 2013-2015 Red Hat, Inc. and/or its affiliates
5  *
6  * Authors:
7  *  Dave Gilbert  <dgilbert@redhat.com>
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  *
12  */
13 
14 /*
15  * Postcopy is a migration technique where the execution flips from the
16  * source to the destination before all the data has been copied.
17  */
18 
19 #include "qemu/osdep.h"
20 #include "qemu/madvise.h"
21 #include "exec/target_page.h"
22 #include "migration.h"
23 #include "qemu-file.h"
24 #include "savevm.h"
25 #include "postcopy-ram.h"
26 #include "ram.h"
27 #include "qapi/error.h"
28 #include "qemu/notify.h"
29 #include "qemu/rcu.h"
30 #include "sysemu/sysemu.h"
31 #include "qemu/error-report.h"
32 #include "trace.h"
33 #include "hw/boards.h"
34 #include "exec/ramblock.h"
35 #include "socket.h"
36 #include "yank_functions.h"
37 #include "tls.h"
38 #include "qemu/userfaultfd.h"
39 #include "qemu/mmap-alloc.h"
40 #include "options.h"
41 
42 /* Arbitrary limit on size of each discard command,
43  * keeps them around ~200 bytes
44  */
45 #define MAX_DISCARDS_PER_COMMAND 12
46 
47 typedef struct PostcopyDiscardState {
48     const char *ramblock_name;
49     uint16_t cur_entry;
50     /*
51      * Start and length of a discard range (bytes)
52      */
53     uint64_t start_list[MAX_DISCARDS_PER_COMMAND];
54     uint64_t length_list[MAX_DISCARDS_PER_COMMAND];
55     unsigned int nsentwords;
56     unsigned int nsentcmds;
57 } PostcopyDiscardState;
58 
59 static NotifierWithReturnList postcopy_notifier_list;
60 
61 void postcopy_infrastructure_init(void)
62 {
63     notifier_with_return_list_init(&postcopy_notifier_list);
64 }
65 
66 void postcopy_add_notifier(NotifierWithReturn *nn)
67 {
68     notifier_with_return_list_add(&postcopy_notifier_list, nn);
69 }
70 
71 void postcopy_remove_notifier(NotifierWithReturn *n)
72 {
73     notifier_with_return_remove(n);
74 }
75 
76 int postcopy_notify(enum PostcopyNotifyReason reason, Error **errp)
77 {
78     struct PostcopyNotifyData pnd;
79     pnd.reason = reason;
80 
81     return notifier_with_return_list_notify(&postcopy_notifier_list,
82                                             &pnd, errp);
83 }
84 
85 /*
86  * NOTE: this routine is not thread safe, we can't call it concurrently. But it
87  * should be good enough for migration's purposes.
88  */
89 void postcopy_thread_create(MigrationIncomingState *mis,
90                             QemuThread *thread, const char *name,
91                             void *(*fn)(void *), int joinable)
92 {
93     qemu_sem_init(&mis->thread_sync_sem, 0);
94     qemu_thread_create(thread, name, fn, mis, joinable);
95     qemu_sem_wait(&mis->thread_sync_sem);
96     qemu_sem_destroy(&mis->thread_sync_sem);
97 }
98 
99 /* Postcopy needs to detect accesses to pages that haven't yet been copied
100  * across, and efficiently map new pages in, the techniques for doing this
101  * are target OS specific.
102  */
103 #if defined(__linux__)
104 #include <poll.h>
105 #include <sys/ioctl.h>
106 #include <sys/syscall.h>
107 #endif
108 
109 #if defined(__linux__) && defined(__NR_userfaultfd) && defined(CONFIG_EVENTFD)
110 #include <sys/eventfd.h>
111 #include <linux/userfaultfd.h>
112 
113 typedef struct PostcopyBlocktimeContext {
114     /* time when page fault initiated per vCPU */
115     uint32_t *page_fault_vcpu_time;
116     /* page address per vCPU */
117     uintptr_t *vcpu_addr;
118     uint32_t total_blocktime;
119     /* blocktime per vCPU */
120     uint32_t *vcpu_blocktime;
121     /* point in time when last page fault was initiated */
122     uint32_t last_begin;
123     /* number of vCPU are suspended */
124     int smp_cpus_down;
125     uint64_t start_time;
126 
127     /*
128      * Handler for exit event, necessary for
129      * releasing whole blocktime_ctx
130      */
131     Notifier exit_notifier;
132 } PostcopyBlocktimeContext;
133 
134 static void destroy_blocktime_context(struct PostcopyBlocktimeContext *ctx)
135 {
136     g_free(ctx->page_fault_vcpu_time);
137     g_free(ctx->vcpu_addr);
138     g_free(ctx->vcpu_blocktime);
139     g_free(ctx);
140 }
141 
142 static void migration_exit_cb(Notifier *n, void *data)
143 {
144     PostcopyBlocktimeContext *ctx = container_of(n, PostcopyBlocktimeContext,
145                                                  exit_notifier);
146     destroy_blocktime_context(ctx);
147 }
148 
149 static struct PostcopyBlocktimeContext *blocktime_context_new(void)
150 {
151     MachineState *ms = MACHINE(qdev_get_machine());
152     unsigned int smp_cpus = ms->smp.cpus;
153     PostcopyBlocktimeContext *ctx = g_new0(PostcopyBlocktimeContext, 1);
154     ctx->page_fault_vcpu_time = g_new0(uint32_t, smp_cpus);
155     ctx->vcpu_addr = g_new0(uintptr_t, smp_cpus);
156     ctx->vcpu_blocktime = g_new0(uint32_t, smp_cpus);
157 
158     ctx->exit_notifier.notify = migration_exit_cb;
159     ctx->start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
160     qemu_add_exit_notifier(&ctx->exit_notifier);
161     return ctx;
162 }
163 
164 static uint32List *get_vcpu_blocktime_list(PostcopyBlocktimeContext *ctx)
165 {
166     MachineState *ms = MACHINE(qdev_get_machine());
167     uint32List *list = NULL;
168     int i;
169 
170     for (i = ms->smp.cpus - 1; i >= 0; i--) {
171         QAPI_LIST_PREPEND(list, ctx->vcpu_blocktime[i]);
172     }
173 
174     return list;
175 }
176 
177 /*
178  * This function just populates MigrationInfo from postcopy's
179  * blocktime context. It will not populate MigrationInfo,
180  * unless postcopy-blocktime capability was set.
181  *
182  * @info: pointer to MigrationInfo to populate
183  */
184 void fill_destination_postcopy_migration_info(MigrationInfo *info)
185 {
186     MigrationIncomingState *mis = migration_incoming_get_current();
187     PostcopyBlocktimeContext *bc = mis->blocktime_ctx;
188 
189     if (!bc) {
190         return;
191     }
192 
193     info->has_postcopy_blocktime = true;
194     info->postcopy_blocktime = bc->total_blocktime;
195     info->has_postcopy_vcpu_blocktime = true;
196     info->postcopy_vcpu_blocktime = get_vcpu_blocktime_list(bc);
197 }
198 
199 static uint32_t get_postcopy_total_blocktime(void)
200 {
201     MigrationIncomingState *mis = migration_incoming_get_current();
202     PostcopyBlocktimeContext *bc = mis->blocktime_ctx;
203 
204     if (!bc) {
205         return 0;
206     }
207 
208     return bc->total_blocktime;
209 }
210 
211 /**
212  * receive_ufd_features: check userfault fd features, to request only supported
213  * features in the future.
214  *
215  * Returns: true on success
216  *
217  * __NR_userfaultfd - should be checked before
218  *  @features: out parameter will contain uffdio_api.features provided by kernel
219  *              in case of success
220  */
221 static bool receive_ufd_features(uint64_t *features)
222 {
223     struct uffdio_api api_struct = {0};
224     int ufd;
225     bool ret = true;
226 
227     ufd = uffd_open(O_CLOEXEC);
228     if (ufd == -1) {
229         error_report("%s: uffd_open() failed: %s", __func__, strerror(errno));
230         return false;
231     }
232 
233     /* ask features */
234     api_struct.api = UFFD_API;
235     api_struct.features = 0;
236     if (ioctl(ufd, UFFDIO_API, &api_struct)) {
237         error_report("%s: UFFDIO_API failed: %s", __func__,
238                      strerror(errno));
239         ret = false;
240         goto release_ufd;
241     }
242 
243     *features = api_struct.features;
244 
245 release_ufd:
246     close(ufd);
247     return ret;
248 }
249 
250 /**
251  * request_ufd_features: this function should be called only once on a newly
252  * opened ufd, subsequent calls will lead to error.
253  *
254  * Returns: true on success
255  *
256  * @ufd: fd obtained from userfaultfd syscall
257  * @features: bit mask see UFFD_API_FEATURES
258  */
259 static bool request_ufd_features(int ufd, uint64_t features)
260 {
261     struct uffdio_api api_struct = {0};
262     uint64_t ioctl_mask;
263 
264     api_struct.api = UFFD_API;
265     api_struct.features = features;
266     if (ioctl(ufd, UFFDIO_API, &api_struct)) {
267         error_report("%s failed: UFFDIO_API failed: %s", __func__,
268                      strerror(errno));
269         return false;
270     }
271 
272     ioctl_mask = 1ULL << _UFFDIO_REGISTER |
273                  1ULL << _UFFDIO_UNREGISTER;
274     if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
275         error_report("Missing userfault features: %" PRIx64,
276                      (uint64_t)(~api_struct.ioctls & ioctl_mask));
277         return false;
278     }
279 
280     return true;
281 }
282 
283 static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis,
284                                 Error **errp)
285 {
286     ERRP_GUARD();
287     uint64_t asked_features = 0;
288     static uint64_t supported_features;
289 
290     /*
291      * it's not possible to
292      * request UFFD_API twice per one fd
293      * userfault fd features is persistent
294      */
295     if (!supported_features) {
296         if (!receive_ufd_features(&supported_features)) {
297             error_setg(errp, "Userfault feature detection failed");
298             return false;
299         }
300     }
301 
302 #ifdef UFFD_FEATURE_THREAD_ID
303     if (UFFD_FEATURE_THREAD_ID & supported_features) {
304         asked_features |= UFFD_FEATURE_THREAD_ID;
305         if (migrate_postcopy_blocktime()) {
306             if (!mis->blocktime_ctx) {
307                 mis->blocktime_ctx = blocktime_context_new();
308             }
309         }
310     }
311 #endif
312 
313     /*
314      * request features, even if asked_features is 0, due to
315      * kernel expects UFFD_API before UFFDIO_REGISTER, per
316      * userfault file descriptor
317      */
318     if (!request_ufd_features(ufd, asked_features)) {
319         error_setg(errp, "Failed features %" PRIu64, asked_features);
320         return false;
321     }
322 
323     if (qemu_real_host_page_size() != ram_pagesize_summary()) {
324         bool have_hp = false;
325         /* We've got a huge page */
326 #ifdef UFFD_FEATURE_MISSING_HUGETLBFS
327         have_hp = supported_features & UFFD_FEATURE_MISSING_HUGETLBFS;
328 #endif
329         if (!have_hp) {
330             error_setg(errp,
331                        "Userfault on this host does not support huge pages");
332             return false;
333         }
334     }
335     return true;
336 }
337 
338 /* Callback from postcopy_ram_supported_by_host block iterator.
339  */
340 static int test_ramblock_postcopiable(RAMBlock *rb, Error **errp)
341 {
342     const char *block_name = qemu_ram_get_idstr(rb);
343     ram_addr_t length = qemu_ram_get_used_length(rb);
344     size_t pagesize = qemu_ram_pagesize(rb);
345     QemuFsType fs;
346 
347     if (length % pagesize) {
348         error_setg(errp,
349                    "Postcopy requires RAM blocks to be a page size multiple,"
350                    " block %s is 0x" RAM_ADDR_FMT " bytes with a "
351                    "page size of 0x%zx", block_name, length, pagesize);
352         return 1;
353     }
354 
355     if (rb->fd >= 0) {
356         fs = qemu_fd_getfs(rb->fd);
357         if (fs != QEMU_FS_TYPE_TMPFS && fs != QEMU_FS_TYPE_HUGETLBFS) {
358             error_setg(errp,
359                        "Host backend files need to be TMPFS or HUGETLBFS only");
360             return 1;
361         }
362     }
363 
364     return 0;
365 }
366 
367 /*
368  * Note: This has the side effect of munlock'ing all of RAM, that's
369  * normally fine since if the postcopy succeeds it gets turned back on at the
370  * end.
371  */
372 bool postcopy_ram_supported_by_host(MigrationIncomingState *mis, Error **errp)
373 {
374     ERRP_GUARD();
375     long pagesize = qemu_real_host_page_size();
376     int ufd = -1;
377     bool ret = false; /* Error unless we change it */
378     void *testarea = NULL;
379     struct uffdio_register reg_struct;
380     struct uffdio_range range_struct;
381     uint64_t feature_mask;
382     RAMBlock *block;
383 
384     if (qemu_target_page_size() > pagesize) {
385         error_setg(errp, "Target page size bigger than host page size");
386         goto out;
387     }
388 
389     ufd = uffd_open(O_CLOEXEC);
390     if (ufd == -1) {
391         error_setg(errp, "Userfaultfd not available: %s", strerror(errno));
392         goto out;
393     }
394 
395     /* Give devices a chance to object */
396     if (postcopy_notify(POSTCOPY_NOTIFY_PROBE, errp)) {
397         goto out;
398     }
399 
400     /* Version and features check */
401     if (!ufd_check_and_apply(ufd, mis, errp)) {
402         goto out;
403     }
404 
405     /*
406      * We don't support postcopy with some type of ramblocks.
407      *
408      * NOTE: we explicitly ignored migrate_ram_is_ignored() instead we checked
409      * all possible ramblocks.  This is because this function can be called
410      * when creating the migration object, during the phase RAM_MIGRATABLE
411      * is not even properly set for all the ramblocks.
412      *
413      * A side effect of this is we'll also check against RAM_SHARED
414      * ramblocks even if migrate_ignore_shared() is set (in which case
415      * we'll never migrate RAM_SHARED at all), but normally this shouldn't
416      * affect in reality, or we can revisit.
417      */
418     RAMBLOCK_FOREACH(block) {
419         if (test_ramblock_postcopiable(block, errp)) {
420             goto out;
421         }
422     }
423 
424     /*
425      * userfault and mlock don't go together; we'll put it back later if
426      * it was enabled.
427      */
428     if (munlockall()) {
429         error_setg(errp, "munlockall() failed: %s", strerror(errno));
430         goto out;
431     }
432 
433     /*
434      *  We need to check that the ops we need are supported on anon memory
435      *  To do that we need to register a chunk and see the flags that
436      *  are returned.
437      */
438     testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE |
439                                     MAP_ANONYMOUS, -1, 0);
440     if (testarea == MAP_FAILED) {
441         error_setg(errp, "Failed to map test area: %s", strerror(errno));
442         goto out;
443     }
444     g_assert(QEMU_PTR_IS_ALIGNED(testarea, pagesize));
445 
446     reg_struct.range.start = (uintptr_t)testarea;
447     reg_struct.range.len = pagesize;
448     reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
449 
450     if (ioctl(ufd, UFFDIO_REGISTER, &reg_struct)) {
451         error_setg(errp, "UFFDIO_REGISTER failed: %s", strerror(errno));
452         goto out;
453     }
454 
455     range_struct.start = (uintptr_t)testarea;
456     range_struct.len = pagesize;
457     if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
458         error_setg(errp, "UFFDIO_UNREGISTER failed: %s", strerror(errno));
459         goto out;
460     }
461 
462     feature_mask = 1ULL << _UFFDIO_WAKE |
463                    1ULL << _UFFDIO_COPY |
464                    1ULL << _UFFDIO_ZEROPAGE;
465     if ((reg_struct.ioctls & feature_mask) != feature_mask) {
466         error_setg(errp, "Missing userfault map features: %" PRIx64,
467                    (uint64_t)(~reg_struct.ioctls & feature_mask));
468         goto out;
469     }
470 
471     /* Success! */
472     ret = true;
473 out:
474     if (testarea) {
475         munmap(testarea, pagesize);
476     }
477     if (ufd != -1) {
478         close(ufd);
479     }
480     return ret;
481 }
482 
483 /*
484  * Setup an area of RAM so that it *can* be used for postcopy later; this
485  * must be done right at the start prior to pre-copy.
486  * opaque should be the MIS.
487  */
488 static int init_range(RAMBlock *rb, void *opaque)
489 {
490     const char *block_name = qemu_ram_get_idstr(rb);
491     void *host_addr = qemu_ram_get_host_addr(rb);
492     ram_addr_t offset = qemu_ram_get_offset(rb);
493     ram_addr_t length = qemu_ram_get_used_length(rb);
494     trace_postcopy_init_range(block_name, host_addr, offset, length);
495 
496     /*
497      * Save the used_length before running the guest. In case we have to
498      * resize RAM blocks when syncing RAM block sizes from the source during
499      * precopy, we'll update it manually via the ram block notifier.
500      */
501     rb->postcopy_length = length;
502 
503     /*
504      * We need the whole of RAM to be truly empty for postcopy, so things
505      * like ROMs and any data tables built during init must be zero'd
506      * - we're going to get the copy from the source anyway.
507      * (Precopy will just overwrite this data, so doesn't need the discard)
508      */
509     if (ram_discard_range(block_name, 0, length)) {
510         return -1;
511     }
512 
513     return 0;
514 }
515 
516 /*
517  * At the end of migration, undo the effects of init_range
518  * opaque should be the MIS.
519  */
520 static int cleanup_range(RAMBlock *rb, void *opaque)
521 {
522     const char *block_name = qemu_ram_get_idstr(rb);
523     void *host_addr = qemu_ram_get_host_addr(rb);
524     ram_addr_t offset = qemu_ram_get_offset(rb);
525     ram_addr_t length = rb->postcopy_length;
526     MigrationIncomingState *mis = opaque;
527     struct uffdio_range range_struct;
528     trace_postcopy_cleanup_range(block_name, host_addr, offset, length);
529 
530     /*
531      * We turned off hugepage for the precopy stage with postcopy enabled
532      * we can turn it back on now.
533      */
534     qemu_madvise(host_addr, length, QEMU_MADV_HUGEPAGE);
535 
536     /*
537      * We can also turn off userfault now since we should have all the
538      * pages.   It can be useful to leave it on to debug postcopy
539      * if you're not sure it's always getting every page.
540      */
541     range_struct.start = (uintptr_t)host_addr;
542     range_struct.len = length;
543 
544     if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) {
545         error_report("%s: userfault unregister %s", __func__, strerror(errno));
546 
547         return -1;
548     }
549 
550     return 0;
551 }
552 
553 /*
554  * Initialise postcopy-ram, setting the RAM to a state where we can go into
555  * postcopy later; must be called prior to any precopy.
556  * called from arch_init's similarly named ram_postcopy_incoming_init
557  */
558 int postcopy_ram_incoming_init(MigrationIncomingState *mis)
559 {
560     if (foreach_not_ignored_block(init_range, NULL)) {
561         return -1;
562     }
563 
564     return 0;
565 }
566 
567 static void postcopy_temp_pages_cleanup(MigrationIncomingState *mis)
568 {
569     int i;
570 
571     if (mis->postcopy_tmp_pages) {
572         for (i = 0; i < mis->postcopy_channels; i++) {
573             if (mis->postcopy_tmp_pages[i].tmp_huge_page) {
574                 munmap(mis->postcopy_tmp_pages[i].tmp_huge_page,
575                        mis->largest_page_size);
576                 mis->postcopy_tmp_pages[i].tmp_huge_page = NULL;
577             }
578         }
579         g_free(mis->postcopy_tmp_pages);
580         mis->postcopy_tmp_pages = NULL;
581     }
582 
583     if (mis->postcopy_tmp_zero_page) {
584         munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size);
585         mis->postcopy_tmp_zero_page = NULL;
586     }
587 }
588 
589 /*
590  * At the end of a migration where postcopy_ram_incoming_init was called.
591  */
592 int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
593 {
594     trace_postcopy_ram_incoming_cleanup_entry();
595 
596     if (mis->preempt_thread_status == PREEMPT_THREAD_CREATED) {
597         /* Notify the fast load thread to quit */
598         mis->preempt_thread_status = PREEMPT_THREAD_QUIT;
599         /*
600          * Update preempt_thread_status before reading count.  Note: mutex
601          * lock only provide ACQUIRE semantic, and it doesn't stops this
602          * write to be reordered after reading the count.
603          */
604         smp_mb();
605         /*
606          * It's possible that the preempt thread is still handling the last
607          * pages to arrive which were requested by guest page faults.
608          * Making sure nothing is left behind by waiting on the condvar if
609          * that unlikely case happened.
610          */
611         WITH_QEMU_LOCK_GUARD(&mis->page_request_mutex) {
612             if (qatomic_read(&mis->page_requested_count)) {
613                 /*
614                  * It is guaranteed to receive a signal later, because the
615                  * count>0 now, so it's destined to be decreased to zero
616                  * very soon by the preempt thread.
617                  */
618                 qemu_cond_wait(&mis->page_request_cond,
619                                &mis->page_request_mutex);
620             }
621         }
622         /* Notify the fast load thread to quit */
623         if (mis->postcopy_qemufile_dst) {
624             qemu_file_shutdown(mis->postcopy_qemufile_dst);
625         }
626         qemu_thread_join(&mis->postcopy_prio_thread);
627         mis->preempt_thread_status = PREEMPT_THREAD_NONE;
628     }
629 
630     if (mis->have_fault_thread) {
631         Error *local_err = NULL;
632 
633         /* Let the fault thread quit */
634         qatomic_set(&mis->fault_thread_quit, 1);
635         postcopy_fault_thread_notify(mis);
636         trace_postcopy_ram_incoming_cleanup_join();
637         qemu_thread_join(&mis->fault_thread);
638 
639         if (postcopy_notify(POSTCOPY_NOTIFY_INBOUND_END, &local_err)) {
640             error_report_err(local_err);
641             return -1;
642         }
643 
644         if (foreach_not_ignored_block(cleanup_range, mis)) {
645             return -1;
646         }
647 
648         trace_postcopy_ram_incoming_cleanup_closeuf();
649         close(mis->userfault_fd);
650         close(mis->userfault_event_fd);
651         mis->have_fault_thread = false;
652     }
653 
654     if (enable_mlock) {
655         if (os_mlock() < 0) {
656             error_report("mlock: %s", strerror(errno));
657             /*
658              * It doesn't feel right to fail at this point, we have a valid
659              * VM state.
660              */
661         }
662     }
663 
664     postcopy_temp_pages_cleanup(mis);
665 
666     trace_postcopy_ram_incoming_cleanup_blocktime(
667             get_postcopy_total_blocktime());
668 
669     trace_postcopy_ram_incoming_cleanup_exit();
670     return 0;
671 }
672 
673 /*
674  * Disable huge pages on an area
675  */
676 static int nhp_range(RAMBlock *rb, void *opaque)
677 {
678     const char *block_name = qemu_ram_get_idstr(rb);
679     void *host_addr = qemu_ram_get_host_addr(rb);
680     ram_addr_t offset = qemu_ram_get_offset(rb);
681     ram_addr_t length = rb->postcopy_length;
682     trace_postcopy_nhp_range(block_name, host_addr, offset, length);
683 
684     /*
685      * Before we do discards we need to ensure those discards really
686      * do delete areas of the page, even if THP thinks a hugepage would
687      * be a good idea, so force hugepages off.
688      */
689     qemu_madvise(host_addr, length, QEMU_MADV_NOHUGEPAGE);
690 
691     return 0;
692 }
693 
694 /*
695  * Userfault requires us to mark RAM as NOHUGEPAGE prior to discard
696  * however leaving it until after precopy means that most of the precopy
697  * data is still THPd
698  */
699 int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
700 {
701     if (foreach_not_ignored_block(nhp_range, mis)) {
702         return -1;
703     }
704 
705     postcopy_state_set(POSTCOPY_INCOMING_DISCARD);
706 
707     return 0;
708 }
709 
710 /*
711  * Mark the given area of RAM as requiring notification to unwritten areas
712  * Used as a  callback on foreach_not_ignored_block.
713  *   host_addr: Base of area to mark
714  *   offset: Offset in the whole ram arena
715  *   length: Length of the section
716  *   opaque: MigrationIncomingState pointer
717  * Returns 0 on success
718  */
719 static int ram_block_enable_notify(RAMBlock *rb, void *opaque)
720 {
721     MigrationIncomingState *mis = opaque;
722     struct uffdio_register reg_struct;
723 
724     reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb);
725     reg_struct.range.len = rb->postcopy_length;
726     reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
727 
728     /* Now tell our userfault_fd that it's responsible for this area */
729     if (ioctl(mis->userfault_fd, UFFDIO_REGISTER, &reg_struct)) {
730         error_report("%s userfault register: %s", __func__, strerror(errno));
731         return -1;
732     }
733     if (!(reg_struct.ioctls & (1ULL << _UFFDIO_COPY))) {
734         error_report("%s userfault: Region doesn't support COPY", __func__);
735         return -1;
736     }
737     if (reg_struct.ioctls & (1ULL << _UFFDIO_ZEROPAGE)) {
738         qemu_ram_set_uf_zeroable(rb);
739     }
740 
741     return 0;
742 }
743 
744 int postcopy_wake_shared(struct PostCopyFD *pcfd,
745                          uint64_t client_addr,
746                          RAMBlock *rb)
747 {
748     size_t pagesize = qemu_ram_pagesize(rb);
749     trace_postcopy_wake_shared(client_addr, qemu_ram_get_idstr(rb));
750     return uffd_wakeup(pcfd->fd,
751                        (void *)(uintptr_t)ROUND_DOWN(client_addr, pagesize),
752                        pagesize);
753 }
754 
755 static int postcopy_request_page(MigrationIncomingState *mis, RAMBlock *rb,
756                                  ram_addr_t start, uint64_t haddr)
757 {
758     void *aligned = (void *)(uintptr_t)ROUND_DOWN(haddr, qemu_ram_pagesize(rb));
759 
760     /*
761      * Discarded pages (via RamDiscardManager) are never migrated. On unlikely
762      * access, place a zeropage, which will also set the relevant bits in the
763      * recv_bitmap accordingly, so we won't try placing a zeropage twice.
764      *
765      * Checking a single bit is sufficient to handle pagesize > TPS as either
766      * all relevant bits are set or not.
767      */
768     assert(QEMU_IS_ALIGNED(start, qemu_ram_pagesize(rb)));
769     if (ramblock_page_is_discarded(rb, start)) {
770         bool received = ramblock_recv_bitmap_test_byte_offset(rb, start);
771 
772         return received ? 0 : postcopy_place_page_zero(mis, aligned, rb);
773     }
774 
775     return migrate_send_rp_req_pages(mis, rb, start, haddr);
776 }
777 
778 /*
779  * Callback from shared fault handlers to ask for a page,
780  * the page must be specified by a RAMBlock and an offset in that rb
781  * Note: Only for use by shared fault handlers (in fault thread)
782  */
783 int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
784                                  uint64_t client_addr, uint64_t rb_offset)
785 {
786     uint64_t aligned_rbo = ROUND_DOWN(rb_offset, qemu_ram_pagesize(rb));
787     MigrationIncomingState *mis = migration_incoming_get_current();
788 
789     trace_postcopy_request_shared_page(pcfd->idstr, qemu_ram_get_idstr(rb),
790                                        rb_offset);
791     if (ramblock_recv_bitmap_test_byte_offset(rb, aligned_rbo)) {
792         trace_postcopy_request_shared_page_present(pcfd->idstr,
793                                         qemu_ram_get_idstr(rb), rb_offset);
794         return postcopy_wake_shared(pcfd, client_addr, rb);
795     }
796     postcopy_request_page(mis, rb, aligned_rbo, client_addr);
797     return 0;
798 }
799 
800 static int get_mem_fault_cpu_index(uint32_t pid)
801 {
802     CPUState *cpu_iter;
803 
804     CPU_FOREACH(cpu_iter) {
805         if (cpu_iter->thread_id == pid) {
806             trace_get_mem_fault_cpu_index(cpu_iter->cpu_index, pid);
807             return cpu_iter->cpu_index;
808         }
809     }
810     trace_get_mem_fault_cpu_index(-1, pid);
811     return -1;
812 }
813 
814 static uint32_t get_low_time_offset(PostcopyBlocktimeContext *dc)
815 {
816     int64_t start_time_offset = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) -
817                                     dc->start_time;
818     return start_time_offset < 1 ? 1 : start_time_offset & UINT32_MAX;
819 }
820 
821 /*
822  * This function is being called when pagefault occurs. It
823  * tracks down vCPU blocking time.
824  *
825  * @addr: faulted host virtual address
826  * @ptid: faulted process thread id
827  * @rb: ramblock appropriate to addr
828  */
829 static void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid,
830                                           RAMBlock *rb)
831 {
832     int cpu, already_received;
833     MigrationIncomingState *mis = migration_incoming_get_current();
834     PostcopyBlocktimeContext *dc = mis->blocktime_ctx;
835     uint32_t low_time_offset;
836 
837     if (!dc || ptid == 0) {
838         return;
839     }
840     cpu = get_mem_fault_cpu_index(ptid);
841     if (cpu < 0) {
842         return;
843     }
844 
845     low_time_offset = get_low_time_offset(dc);
846     if (dc->vcpu_addr[cpu] == 0) {
847         qatomic_inc(&dc->smp_cpus_down);
848     }
849 
850     qatomic_xchg(&dc->last_begin, low_time_offset);
851     qatomic_xchg(&dc->page_fault_vcpu_time[cpu], low_time_offset);
852     qatomic_xchg(&dc->vcpu_addr[cpu], addr);
853 
854     /*
855      * check it here, not at the beginning of the function,
856      * due to, check could occur early than bitmap_set in
857      * qemu_ufd_copy_ioctl
858      */
859     already_received = ramblock_recv_bitmap_test(rb, (void *)addr);
860     if (already_received) {
861         qatomic_xchg(&dc->vcpu_addr[cpu], 0);
862         qatomic_xchg(&dc->page_fault_vcpu_time[cpu], 0);
863         qatomic_dec(&dc->smp_cpus_down);
864     }
865     trace_mark_postcopy_blocktime_begin(addr, dc, dc->page_fault_vcpu_time[cpu],
866                                         cpu, already_received);
867 }
868 
869 /*
870  *  This function just provide calculated blocktime per cpu and trace it.
871  *  Total blocktime is calculated in mark_postcopy_blocktime_end.
872  *
873  *
874  * Assume we have 3 CPU
875  *
876  *      S1        E1           S1               E1
877  * -----***********------------xxx***************------------------------> CPU1
878  *
879  *             S2                E2
880  * ------------****************xxx---------------------------------------> CPU2
881  *
882  *                         S3            E3
883  * ------------------------****xxx********-------------------------------> CPU3
884  *
885  * We have sequence S1,S2,E1,S3,S1,E2,E3,E1
886  * S2,E1 - doesn't match condition due to sequence S1,S2,E1 doesn't include CPU3
887  * S3,S1,E2 - sequence includes all CPUs, in this case overlap will be S1,E2 -
888  *            it's a part of total blocktime.
889  * S1 - here is last_begin
890  * Legend of the picture is following:
891  *              * - means blocktime per vCPU
892  *              x - means overlapped blocktime (total blocktime)
893  *
894  * @addr: host virtual address
895  */
896 static void mark_postcopy_blocktime_end(uintptr_t addr)
897 {
898     MigrationIncomingState *mis = migration_incoming_get_current();
899     PostcopyBlocktimeContext *dc = mis->blocktime_ctx;
900     MachineState *ms = MACHINE(qdev_get_machine());
901     unsigned int smp_cpus = ms->smp.cpus;
902     int i, affected_cpu = 0;
903     bool vcpu_total_blocktime = false;
904     uint32_t read_vcpu_time, low_time_offset;
905 
906     if (!dc) {
907         return;
908     }
909 
910     low_time_offset = get_low_time_offset(dc);
911     /* lookup cpu, to clear it,
912      * that algorithm looks straightforward, but it's not
913      * optimal, more optimal algorithm is keeping tree or hash
914      * where key is address value is a list of  */
915     for (i = 0; i < smp_cpus; i++) {
916         uint32_t vcpu_blocktime = 0;
917 
918         read_vcpu_time = qatomic_fetch_add(&dc->page_fault_vcpu_time[i], 0);
919         if (qatomic_fetch_add(&dc->vcpu_addr[i], 0) != addr ||
920             read_vcpu_time == 0) {
921             continue;
922         }
923         qatomic_xchg(&dc->vcpu_addr[i], 0);
924         vcpu_blocktime = low_time_offset - read_vcpu_time;
925         affected_cpu += 1;
926         /* we need to know is that mark_postcopy_end was due to
927          * faulted page, another possible case it's prefetched
928          * page and in that case we shouldn't be here */
929         if (!vcpu_total_blocktime &&
930             qatomic_fetch_add(&dc->smp_cpus_down, 0) == smp_cpus) {
931             vcpu_total_blocktime = true;
932         }
933         /* continue cycle, due to one page could affect several vCPUs */
934         dc->vcpu_blocktime[i] += vcpu_blocktime;
935     }
936 
937     qatomic_sub(&dc->smp_cpus_down, affected_cpu);
938     if (vcpu_total_blocktime) {
939         dc->total_blocktime += low_time_offset - qatomic_fetch_add(
940                 &dc->last_begin, 0);
941     }
942     trace_mark_postcopy_blocktime_end(addr, dc, dc->total_blocktime,
943                                       affected_cpu);
944 }
945 
946 static void postcopy_pause_fault_thread(MigrationIncomingState *mis)
947 {
948     trace_postcopy_pause_fault_thread();
949     qemu_sem_wait(&mis->postcopy_pause_sem_fault);
950     trace_postcopy_pause_fault_thread_continued();
951 }
952 
953 /*
954  * Handle faults detected by the USERFAULT markings
955  */
956 static void *postcopy_ram_fault_thread(void *opaque)
957 {
958     MigrationIncomingState *mis = opaque;
959     struct uffd_msg msg;
960     int ret;
961     size_t index;
962     RAMBlock *rb = NULL;
963 
964     trace_postcopy_ram_fault_thread_entry();
965     rcu_register_thread();
966     mis->last_rb = NULL; /* last RAMBlock we sent part of */
967     qemu_sem_post(&mis->thread_sync_sem);
968 
969     struct pollfd *pfd;
970     size_t pfd_len = 2 + mis->postcopy_remote_fds->len;
971 
972     pfd = g_new0(struct pollfd, pfd_len);
973 
974     pfd[0].fd = mis->userfault_fd;
975     pfd[0].events = POLLIN;
976     pfd[1].fd = mis->userfault_event_fd;
977     pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */
978     trace_postcopy_ram_fault_thread_fds_core(pfd[0].fd, pfd[1].fd);
979     for (index = 0; index < mis->postcopy_remote_fds->len; index++) {
980         struct PostCopyFD *pcfd = &g_array_index(mis->postcopy_remote_fds,
981                                                  struct PostCopyFD, index);
982         pfd[2 + index].fd = pcfd->fd;
983         pfd[2 + index].events = POLLIN;
984         trace_postcopy_ram_fault_thread_fds_extra(2 + index, pcfd->idstr,
985                                                   pcfd->fd);
986     }
987 
988     while (true) {
989         ram_addr_t rb_offset;
990         int poll_result;
991 
992         /*
993          * We're mainly waiting for the kernel to give us a faulting HVA,
994          * however we can be told to quit via userfault_quit_fd which is
995          * an eventfd
996          */
997 
998         poll_result = poll(pfd, pfd_len, -1 /* Wait forever */);
999         if (poll_result == -1) {
1000             error_report("%s: userfault poll: %s", __func__, strerror(errno));
1001             break;
1002         }
1003 
1004         if (!mis->to_src_file) {
1005             /*
1006              * Possibly someone tells us that the return path is
1007              * broken already using the event. We should hold until
1008              * the channel is rebuilt.
1009              */
1010             postcopy_pause_fault_thread(mis);
1011         }
1012 
1013         if (pfd[1].revents) {
1014             uint64_t tmp64 = 0;
1015 
1016             /* Consume the signal */
1017             if (read(mis->userfault_event_fd, &tmp64, 8) != 8) {
1018                 /* Nothing obviously nicer than posting this error. */
1019                 error_report("%s: read() failed", __func__);
1020             }
1021 
1022             if (qatomic_read(&mis->fault_thread_quit)) {
1023                 trace_postcopy_ram_fault_thread_quit();
1024                 break;
1025             }
1026         }
1027 
1028         if (pfd[0].revents) {
1029             poll_result--;
1030             ret = read(mis->userfault_fd, &msg, sizeof(msg));
1031             if (ret != sizeof(msg)) {
1032                 if (errno == EAGAIN) {
1033                     /*
1034                      * if a wake up happens on the other thread just after
1035                      * the poll, there is nothing to read.
1036                      */
1037                     continue;
1038                 }
1039                 if (ret < 0) {
1040                     error_report("%s: Failed to read full userfault "
1041                                  "message: %s",
1042                                  __func__, strerror(errno));
1043                     break;
1044                 } else {
1045                     error_report("%s: Read %d bytes from userfaultfd "
1046                                  "expected %zd",
1047                                  __func__, ret, sizeof(msg));
1048                     break; /* Lost alignment, don't know what we'd read next */
1049                 }
1050             }
1051             if (msg.event != UFFD_EVENT_PAGEFAULT) {
1052                 error_report("%s: Read unexpected event %ud from userfaultfd",
1053                              __func__, msg.event);
1054                 continue; /* It's not a page fault, shouldn't happen */
1055             }
1056 
1057             rb = qemu_ram_block_from_host(
1058                      (void *)(uintptr_t)msg.arg.pagefault.address,
1059                      true, &rb_offset);
1060             if (!rb) {
1061                 error_report("postcopy_ram_fault_thread: Fault outside guest: %"
1062                              PRIx64, (uint64_t)msg.arg.pagefault.address);
1063                 break;
1064             }
1065 
1066             rb_offset = ROUND_DOWN(rb_offset, qemu_ram_pagesize(rb));
1067             trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
1068                                                 qemu_ram_get_idstr(rb),
1069                                                 rb_offset,
1070                                                 msg.arg.pagefault.feat.ptid);
1071             mark_postcopy_blocktime_begin(
1072                     (uintptr_t)(msg.arg.pagefault.address),
1073                                 msg.arg.pagefault.feat.ptid, rb);
1074 
1075 retry:
1076             /*
1077              * Send the request to the source - we want to request one
1078              * of our host page sizes (which is >= TPS)
1079              */
1080             ret = postcopy_request_page(mis, rb, rb_offset,
1081                                         msg.arg.pagefault.address);
1082             if (ret) {
1083                 /* May be network failure, try to wait for recovery */
1084                 postcopy_pause_fault_thread(mis);
1085                 goto retry;
1086             }
1087         }
1088 
1089         /* Now handle any requests from external processes on shared memory */
1090         /* TODO: May need to handle devices deregistering during postcopy */
1091         for (index = 2; index < pfd_len && poll_result; index++) {
1092             if (pfd[index].revents) {
1093                 struct PostCopyFD *pcfd =
1094                     &g_array_index(mis->postcopy_remote_fds,
1095                                    struct PostCopyFD, index - 2);
1096 
1097                 poll_result--;
1098                 if (pfd[index].revents & POLLERR) {
1099                     error_report("%s: POLLERR on poll %zd fd=%d",
1100                                  __func__, index, pcfd->fd);
1101                     pfd[index].events = 0;
1102                     continue;
1103                 }
1104 
1105                 ret = read(pcfd->fd, &msg, sizeof(msg));
1106                 if (ret != sizeof(msg)) {
1107                     if (errno == EAGAIN) {
1108                         /*
1109                          * if a wake up happens on the other thread just after
1110                          * the poll, there is nothing to read.
1111                          */
1112                         continue;
1113                     }
1114                     if (ret < 0) {
1115                         error_report("%s: Failed to read full userfault "
1116                                      "message: %s (shared) revents=%d",
1117                                      __func__, strerror(errno),
1118                                      pfd[index].revents);
1119                         /*TODO: Could just disable this sharer */
1120                         break;
1121                     } else {
1122                         error_report("%s: Read %d bytes from userfaultfd "
1123                                      "expected %zd (shared)",
1124                                      __func__, ret, sizeof(msg));
1125                         /*TODO: Could just disable this sharer */
1126                         break; /*Lost alignment,don't know what we'd read next*/
1127                     }
1128                 }
1129                 if (msg.event != UFFD_EVENT_PAGEFAULT) {
1130                     error_report("%s: Read unexpected event %ud "
1131                                  "from userfaultfd (shared)",
1132                                  __func__, msg.event);
1133                     continue; /* It's not a page fault, shouldn't happen */
1134                 }
1135                 /* Call the device handler registered with us */
1136                 ret = pcfd->handler(pcfd, &msg);
1137                 if (ret) {
1138                     error_report("%s: Failed to resolve shared fault on %zd/%s",
1139                                  __func__, index, pcfd->idstr);
1140                     /* TODO: Fail? Disable this sharer? */
1141                 }
1142             }
1143         }
1144     }
1145     rcu_unregister_thread();
1146     trace_postcopy_ram_fault_thread_exit();
1147     g_free(pfd);
1148     return NULL;
1149 }
1150 
1151 static int postcopy_temp_pages_setup(MigrationIncomingState *mis)
1152 {
1153     PostcopyTmpPage *tmp_page;
1154     int err, i, channels;
1155     void *temp_page;
1156 
1157     if (migrate_postcopy_preempt()) {
1158         /* If preemption enabled, need extra channel for urgent requests */
1159         mis->postcopy_channels = RAM_CHANNEL_MAX;
1160     } else {
1161         /* Both precopy/postcopy on the same channel */
1162         mis->postcopy_channels = 1;
1163     }
1164 
1165     channels = mis->postcopy_channels;
1166     mis->postcopy_tmp_pages = g_malloc0_n(sizeof(PostcopyTmpPage), channels);
1167 
1168     for (i = 0; i < channels; i++) {
1169         tmp_page = &mis->postcopy_tmp_pages[i];
1170         temp_page = mmap(NULL, mis->largest_page_size, PROT_READ | PROT_WRITE,
1171                          MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
1172         if (temp_page == MAP_FAILED) {
1173             err = errno;
1174             error_report("%s: Failed to map postcopy_tmp_pages[%d]: %s",
1175                          __func__, i, strerror(err));
1176             /* Clean up will be done later */
1177             return -err;
1178         }
1179         tmp_page->tmp_huge_page = temp_page;
1180         /* Initialize default states for each tmp page */
1181         postcopy_temp_page_reset(tmp_page);
1182     }
1183 
1184     /*
1185      * Map large zero page when kernel can't use UFFDIO_ZEROPAGE for hugepages
1186      */
1187     mis->postcopy_tmp_zero_page = mmap(NULL, mis->largest_page_size,
1188                                        PROT_READ | PROT_WRITE,
1189                                        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
1190     if (mis->postcopy_tmp_zero_page == MAP_FAILED) {
1191         err = errno;
1192         mis->postcopy_tmp_zero_page = NULL;
1193         error_report("%s: Failed to map large zero page %s",
1194                      __func__, strerror(err));
1195         return -err;
1196     }
1197 
1198     memset(mis->postcopy_tmp_zero_page, '\0', mis->largest_page_size);
1199 
1200     return 0;
1201 }
1202 
1203 int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
1204 {
1205     Error *local_err = NULL;
1206 
1207     /* Open the fd for the kernel to give us userfaults */
1208     mis->userfault_fd = uffd_open(O_CLOEXEC | O_NONBLOCK);
1209     if (mis->userfault_fd == -1) {
1210         error_report("%s: Failed to open userfault fd: %s", __func__,
1211                      strerror(errno));
1212         return -1;
1213     }
1214 
1215     /*
1216      * Although the host check already tested the API, we need to
1217      * do the check again as an ABI handshake on the new fd.
1218      */
1219     if (!ufd_check_and_apply(mis->userfault_fd, mis, &local_err)) {
1220         error_report_err(local_err);
1221         return -1;
1222     }
1223 
1224     /* Now an eventfd we use to tell the fault-thread to quit */
1225     mis->userfault_event_fd = eventfd(0, EFD_CLOEXEC);
1226     if (mis->userfault_event_fd == -1) {
1227         error_report("%s: Opening userfault_event_fd: %s", __func__,
1228                      strerror(errno));
1229         close(mis->userfault_fd);
1230         return -1;
1231     }
1232 
1233     postcopy_thread_create(mis, &mis->fault_thread,
1234                            MIGRATION_THREAD_DST_FAULT,
1235                            postcopy_ram_fault_thread, QEMU_THREAD_JOINABLE);
1236     mis->have_fault_thread = true;
1237 
1238     /* Mark so that we get notified of accesses to unwritten areas */
1239     if (foreach_not_ignored_block(ram_block_enable_notify, mis)) {
1240         error_report("ram_block_enable_notify failed");
1241         return -1;
1242     }
1243 
1244     if (postcopy_temp_pages_setup(mis)) {
1245         /* Error dumped in the sub-function */
1246         return -1;
1247     }
1248 
1249     if (migrate_postcopy_preempt()) {
1250         /*
1251          * This thread needs to be created after the temp pages because
1252          * it'll fetch RAM_CHANNEL_POSTCOPY PostcopyTmpPage immediately.
1253          */
1254         postcopy_thread_create(mis, &mis->postcopy_prio_thread,
1255                                MIGRATION_THREAD_DST_PREEMPT,
1256                                postcopy_preempt_thread, QEMU_THREAD_JOINABLE);
1257         mis->preempt_thread_status = PREEMPT_THREAD_CREATED;
1258     }
1259 
1260     trace_postcopy_ram_enable_notify();
1261 
1262     return 0;
1263 }
1264 
1265 static int qemu_ufd_copy_ioctl(MigrationIncomingState *mis, void *host_addr,
1266                                void *from_addr, uint64_t pagesize, RAMBlock *rb)
1267 {
1268     int userfault_fd = mis->userfault_fd;
1269     int ret;
1270 
1271     if (from_addr) {
1272         ret = uffd_copy_page(userfault_fd, host_addr, from_addr, pagesize,
1273                              false);
1274     } else {
1275         ret = uffd_zero_page(userfault_fd, host_addr, pagesize, false);
1276     }
1277     if (!ret) {
1278         qemu_mutex_lock(&mis->page_request_mutex);
1279         ramblock_recv_bitmap_set_range(rb, host_addr,
1280                                        pagesize / qemu_target_page_size());
1281         /*
1282          * If this page resolves a page fault for a previous recorded faulted
1283          * address, take a special note to maintain the requested page list.
1284          */
1285         if (g_tree_lookup(mis->page_requested, host_addr)) {
1286             g_tree_remove(mis->page_requested, host_addr);
1287             int left_pages = qatomic_dec_fetch(&mis->page_requested_count);
1288 
1289             trace_postcopy_page_req_del(host_addr, mis->page_requested_count);
1290             /* Order the update of count and read of preempt status */
1291             smp_mb();
1292             if (mis->preempt_thread_status == PREEMPT_THREAD_QUIT &&
1293                 left_pages == 0) {
1294                 /*
1295                  * This probably means the main thread is waiting for us.
1296                  * Notify that we've finished receiving the last requested
1297                  * page.
1298                  */
1299                 qemu_cond_signal(&mis->page_request_cond);
1300             }
1301         }
1302         qemu_mutex_unlock(&mis->page_request_mutex);
1303         mark_postcopy_blocktime_end((uintptr_t)host_addr);
1304     }
1305     return ret;
1306 }
1307 
1308 int postcopy_notify_shared_wake(RAMBlock *rb, uint64_t offset)
1309 {
1310     int i;
1311     MigrationIncomingState *mis = migration_incoming_get_current();
1312     GArray *pcrfds = mis->postcopy_remote_fds;
1313 
1314     for (i = 0; i < pcrfds->len; i++) {
1315         struct PostCopyFD *cur = &g_array_index(pcrfds, struct PostCopyFD, i);
1316         int ret = cur->waker(cur, rb, offset);
1317         if (ret) {
1318             return ret;
1319         }
1320     }
1321     return 0;
1322 }
1323 
1324 /*
1325  * Place a host page (from) at (host) atomically
1326  * returns 0 on success
1327  */
1328 int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
1329                         RAMBlock *rb)
1330 {
1331     size_t pagesize = qemu_ram_pagesize(rb);
1332     int e;
1333 
1334     /* copy also acks to the kernel waking the stalled thread up
1335      * TODO: We can inhibit that ack and only do it if it was requested
1336      * which would be slightly cheaper, but we'd have to be careful
1337      * of the order of updating our page state.
1338      */
1339     e = qemu_ufd_copy_ioctl(mis, host, from, pagesize, rb);
1340     if (e) {
1341         return e;
1342     }
1343 
1344     trace_postcopy_place_page(host);
1345     return postcopy_notify_shared_wake(rb,
1346                                        qemu_ram_block_host_offset(rb, host));
1347 }
1348 
1349 /*
1350  * Place a zero page at (host) atomically
1351  * returns 0 on success
1352  */
1353 int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
1354                              RAMBlock *rb)
1355 {
1356     size_t pagesize = qemu_ram_pagesize(rb);
1357     trace_postcopy_place_page_zero(host);
1358 
1359     /* Normal RAMBlocks can zero a page using UFFDIO_ZEROPAGE
1360      * but it's not available for everything (e.g. hugetlbpages)
1361      */
1362     if (qemu_ram_is_uf_zeroable(rb)) {
1363         int e;
1364         e = qemu_ufd_copy_ioctl(mis, host, NULL, pagesize, rb);
1365         if (e) {
1366             return e;
1367         }
1368         return postcopy_notify_shared_wake(rb,
1369                                            qemu_ram_block_host_offset(rb,
1370                                                                       host));
1371     } else {
1372         return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page, rb);
1373     }
1374 }
1375 
1376 #else
1377 /* No target OS support, stubs just fail */
1378 void fill_destination_postcopy_migration_info(MigrationInfo *info)
1379 {
1380 }
1381 
1382 bool postcopy_ram_supported_by_host(MigrationIncomingState *mis, Error **errp)
1383 {
1384     error_report("%s: No OS support", __func__);
1385     return false;
1386 }
1387 
1388 int postcopy_ram_incoming_init(MigrationIncomingState *mis)
1389 {
1390     error_report("postcopy_ram_incoming_init: No OS support");
1391     return -1;
1392 }
1393 
1394 int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
1395 {
1396     g_assert_not_reached();
1397 }
1398 
1399 int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
1400 {
1401     g_assert_not_reached();
1402 }
1403 
1404 int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
1405                                  uint64_t client_addr, uint64_t rb_offset)
1406 {
1407     g_assert_not_reached();
1408 }
1409 
1410 int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
1411 {
1412     g_assert_not_reached();
1413 }
1414 
1415 int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
1416                         RAMBlock *rb)
1417 {
1418     g_assert_not_reached();
1419 }
1420 
1421 int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
1422                         RAMBlock *rb)
1423 {
1424     g_assert_not_reached();
1425 }
1426 
1427 int postcopy_wake_shared(struct PostCopyFD *pcfd,
1428                          uint64_t client_addr,
1429                          RAMBlock *rb)
1430 {
1431     g_assert_not_reached();
1432 }
1433 #endif
1434 
1435 /* ------------------------------------------------------------------------- */
1436 void postcopy_temp_page_reset(PostcopyTmpPage *tmp_page)
1437 {
1438     tmp_page->target_pages = 0;
1439     tmp_page->host_addr = NULL;
1440     /*
1441      * This is set to true when reset, and cleared as long as we received any
1442      * of the non-zero small page within this huge page.
1443      */
1444     tmp_page->all_zero = true;
1445 }
1446 
1447 void postcopy_fault_thread_notify(MigrationIncomingState *mis)
1448 {
1449     uint64_t tmp64 = 1;
1450 
1451     /*
1452      * Wakeup the fault_thread.  It's an eventfd that should currently
1453      * be at 0, we're going to increment it to 1
1454      */
1455     if (write(mis->userfault_event_fd, &tmp64, 8) != 8) {
1456         /* Not much we can do here, but may as well report it */
1457         error_report("%s: incrementing failed: %s", __func__,
1458                      strerror(errno));
1459     }
1460 }
1461 
1462 /**
1463  * postcopy_discard_send_init: Called at the start of each RAMBlock before
1464  *   asking to discard individual ranges.
1465  *
1466  * @ms: The current migration state.
1467  * @offset: the bitmap offset of the named RAMBlock in the migration bitmap.
1468  * @name: RAMBlock that discards will operate on.
1469  */
1470 static PostcopyDiscardState pds = {0};
1471 void postcopy_discard_send_init(MigrationState *ms, const char *name)
1472 {
1473     pds.ramblock_name = name;
1474     pds.cur_entry = 0;
1475     pds.nsentwords = 0;
1476     pds.nsentcmds = 0;
1477 }
1478 
1479 /**
1480  * postcopy_discard_send_range: Called by the bitmap code for each chunk to
1481  *   discard. May send a discard message, may just leave it queued to
1482  *   be sent later.
1483  *
1484  * @ms: Current migration state.
1485  * @start,@length: a range of pages in the migration bitmap in the
1486  *   RAM block passed to postcopy_discard_send_init() (length=1 is one page)
1487  */
1488 void postcopy_discard_send_range(MigrationState *ms, unsigned long start,
1489                                  unsigned long length)
1490 {
1491     size_t tp_size = qemu_target_page_size();
1492     /* Convert to byte offsets within the RAM block */
1493     pds.start_list[pds.cur_entry] = start  * tp_size;
1494     pds.length_list[pds.cur_entry] = length * tp_size;
1495     trace_postcopy_discard_send_range(pds.ramblock_name, start, length);
1496     pds.cur_entry++;
1497     pds.nsentwords++;
1498 
1499     if (pds.cur_entry == MAX_DISCARDS_PER_COMMAND) {
1500         /* Full set, ship it! */
1501         qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
1502                                               pds.ramblock_name,
1503                                               pds.cur_entry,
1504                                               pds.start_list,
1505                                               pds.length_list);
1506         pds.nsentcmds++;
1507         pds.cur_entry = 0;
1508     }
1509 }
1510 
1511 /**
1512  * postcopy_discard_send_finish: Called at the end of each RAMBlock by the
1513  * bitmap code. Sends any outstanding discard messages, frees the PDS
1514  *
1515  * @ms: Current migration state.
1516  */
1517 void postcopy_discard_send_finish(MigrationState *ms)
1518 {
1519     /* Anything unsent? */
1520     if (pds.cur_entry) {
1521         qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
1522                                               pds.ramblock_name,
1523                                               pds.cur_entry,
1524                                               pds.start_list,
1525                                               pds.length_list);
1526         pds.nsentcmds++;
1527     }
1528 
1529     trace_postcopy_discard_send_finish(pds.ramblock_name, pds.nsentwords,
1530                                        pds.nsentcmds);
1531 }
1532 
1533 /*
1534  * Current state of incoming postcopy; note this is not part of
1535  * MigrationIncomingState since it's state is used during cleanup
1536  * at the end as MIS is being freed.
1537  */
1538 static PostcopyState incoming_postcopy_state;
1539 
1540 PostcopyState  postcopy_state_get(void)
1541 {
1542     return qatomic_load_acquire(&incoming_postcopy_state);
1543 }
1544 
1545 /* Set the state and return the old state */
1546 PostcopyState postcopy_state_set(PostcopyState new_state)
1547 {
1548     return qatomic_xchg(&incoming_postcopy_state, new_state);
1549 }
1550 
1551 /* Register a handler for external shared memory postcopy
1552  * called on the destination.
1553  */
1554 void postcopy_register_shared_ufd(struct PostCopyFD *pcfd)
1555 {
1556     MigrationIncomingState *mis = migration_incoming_get_current();
1557 
1558     mis->postcopy_remote_fds = g_array_append_val(mis->postcopy_remote_fds,
1559                                                   *pcfd);
1560 }
1561 
1562 /* Unregister a handler for external shared memory postcopy
1563  */
1564 void postcopy_unregister_shared_ufd(struct PostCopyFD *pcfd)
1565 {
1566     guint i;
1567     MigrationIncomingState *mis = migration_incoming_get_current();
1568     GArray *pcrfds = mis->postcopy_remote_fds;
1569 
1570     if (!pcrfds) {
1571         /* migration has already finished and freed the array */
1572         return;
1573     }
1574     for (i = 0; i < pcrfds->len; i++) {
1575         struct PostCopyFD *cur = &g_array_index(pcrfds, struct PostCopyFD, i);
1576         if (cur->fd == pcfd->fd) {
1577             mis->postcopy_remote_fds = g_array_remove_index(pcrfds, i);
1578             return;
1579         }
1580     }
1581 }
1582 
1583 void postcopy_preempt_new_channel(MigrationIncomingState *mis, QEMUFile *file)
1584 {
1585     /*
1586      * The new loading channel has its own threads, so it needs to be
1587      * blocked too.  It's by default true, just be explicit.
1588      */
1589     qemu_file_set_blocking(file, true);
1590     mis->postcopy_qemufile_dst = file;
1591     qemu_sem_post(&mis->postcopy_qemufile_dst_done);
1592     trace_postcopy_preempt_new_channel();
1593 }
1594 
1595 /*
1596  * Setup the postcopy preempt channel with the IOC.  If ERROR is specified,
1597  * setup the error instead.  This helper will free the ERROR if specified.
1598  */
1599 static void
1600 postcopy_preempt_send_channel_done(MigrationState *s,
1601                                    QIOChannel *ioc, Error *local_err)
1602 {
1603     if (local_err) {
1604         migrate_set_error(s, local_err);
1605         error_free(local_err);
1606     } else {
1607         migration_ioc_register_yank(ioc);
1608         s->postcopy_qemufile_src = qemu_file_new_output(ioc);
1609         trace_postcopy_preempt_new_channel();
1610     }
1611 
1612     /*
1613      * Kick the waiter in all cases.  The waiter should check upon
1614      * postcopy_qemufile_src to know whether it failed or not.
1615      */
1616     qemu_sem_post(&s->postcopy_qemufile_src_sem);
1617 }
1618 
1619 static void
1620 postcopy_preempt_tls_handshake(QIOTask *task, gpointer opaque)
1621 {
1622     g_autoptr(QIOChannel) ioc = QIO_CHANNEL(qio_task_get_source(task));
1623     MigrationState *s = opaque;
1624     Error *local_err = NULL;
1625 
1626     qio_task_propagate_error(task, &local_err);
1627     postcopy_preempt_send_channel_done(s, ioc, local_err);
1628 }
1629 
1630 static void
1631 postcopy_preempt_send_channel_new(QIOTask *task, gpointer opaque)
1632 {
1633     g_autoptr(QIOChannel) ioc = QIO_CHANNEL(qio_task_get_source(task));
1634     MigrationState *s = opaque;
1635     QIOChannelTLS *tioc;
1636     Error *local_err = NULL;
1637 
1638     if (qio_task_propagate_error(task, &local_err)) {
1639         goto out;
1640     }
1641 
1642     if (migrate_channel_requires_tls_upgrade(ioc)) {
1643         tioc = migration_tls_client_create(ioc, s->hostname, &local_err);
1644         if (!tioc) {
1645             goto out;
1646         }
1647         trace_postcopy_preempt_tls_handshake();
1648         qio_channel_set_name(QIO_CHANNEL(tioc), "migration-tls-preempt");
1649         qio_channel_tls_handshake(tioc, postcopy_preempt_tls_handshake,
1650                                   s, NULL, NULL);
1651         /* Setup the channel until TLS handshake finished */
1652         return;
1653     }
1654 
1655 out:
1656     /* This handles both good and error cases */
1657     postcopy_preempt_send_channel_done(s, ioc, local_err);
1658 }
1659 
1660 /*
1661  * This function will kick off an async task to establish the preempt
1662  * channel, and wait until the connection setup completed.  Returns 0 if
1663  * channel established, -1 for error.
1664  */
1665 int postcopy_preempt_establish_channel(MigrationState *s)
1666 {
1667     /* If preempt not enabled, no need to wait */
1668     if (!migrate_postcopy_preempt()) {
1669         return 0;
1670     }
1671 
1672     /*
1673      * Kick off async task to establish preempt channel.  Only do so with
1674      * 8.0+ machines, because 7.1/7.2 require the channel to be created in
1675      * setup phase of migration (even if racy in an unreliable network).
1676      */
1677     if (!s->preempt_pre_7_2) {
1678         postcopy_preempt_setup(s);
1679     }
1680 
1681     /*
1682      * We need the postcopy preempt channel to be established before
1683      * starting doing anything.
1684      */
1685     qemu_sem_wait(&s->postcopy_qemufile_src_sem);
1686 
1687     return s->postcopy_qemufile_src ? 0 : -1;
1688 }
1689 
1690 void postcopy_preempt_setup(MigrationState *s)
1691 {
1692     /* Kick an async task to connect */
1693     socket_send_channel_create(postcopy_preempt_send_channel_new, s);
1694 }
1695 
1696 static void postcopy_pause_ram_fast_load(MigrationIncomingState *mis)
1697 {
1698     trace_postcopy_pause_fast_load();
1699     qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex);
1700     qemu_sem_wait(&mis->postcopy_pause_sem_fast_load);
1701     qemu_mutex_lock(&mis->postcopy_prio_thread_mutex);
1702     trace_postcopy_pause_fast_load_continued();
1703 }
1704 
1705 static bool preempt_thread_should_run(MigrationIncomingState *mis)
1706 {
1707     return mis->preempt_thread_status != PREEMPT_THREAD_QUIT;
1708 }
1709 
1710 void *postcopy_preempt_thread(void *opaque)
1711 {
1712     MigrationIncomingState *mis = opaque;
1713     int ret;
1714 
1715     trace_postcopy_preempt_thread_entry();
1716 
1717     rcu_register_thread();
1718 
1719     qemu_sem_post(&mis->thread_sync_sem);
1720 
1721     /*
1722      * The preempt channel is established in asynchronous way.  Wait
1723      * for its completion.
1724      */
1725     qemu_sem_wait(&mis->postcopy_qemufile_dst_done);
1726 
1727     /* Sending RAM_SAVE_FLAG_EOS to terminate this thread */
1728     qemu_mutex_lock(&mis->postcopy_prio_thread_mutex);
1729     while (preempt_thread_should_run(mis)) {
1730         ret = ram_load_postcopy(mis->postcopy_qemufile_dst,
1731                                 RAM_CHANNEL_POSTCOPY);
1732         /* If error happened, go into recovery routine */
1733         if (ret && preempt_thread_should_run(mis)) {
1734             postcopy_pause_ram_fast_load(mis);
1735         } else {
1736             /* We're done */
1737             break;
1738         }
1739     }
1740     qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex);
1741 
1742     rcu_unregister_thread();
1743 
1744     trace_postcopy_preempt_thread_exit();
1745 
1746     return NULL;
1747 }
1748 
1749 bool postcopy_is_paused(MigrationStatus status)
1750 {
1751     return status == MIGRATION_STATUS_POSTCOPY_PAUSED ||
1752         status == MIGRATION_STATUS_POSTCOPY_RECOVER_SETUP;
1753 }
1754