/* * Postcopy migration for RAM * * Copyright 2013-2015 Red Hat, Inc. and/or its affiliates * * Authors: * Dave Gilbert * * This work is licensed under the terms of the GNU GPL, version 2 or later. * See the COPYING file in the top-level directory. * */ /* * Postcopy is a migration technique where the execution flips from the * source to the destination before all the data has been copied. */ #include "qemu/osdep.h" #include "exec/target_page.h" #include "migration.h" #include "qemu-file.h" #include "savevm.h" #include "postcopy-ram.h" #include "ram.h" #include "qapi/error.h" #include "qemu/notify.h" #include "qemu/rcu.h" #include "sysemu/sysemu.h" #include "sysemu/balloon.h" #include "qemu/error-report.h" #include "trace.h" #include "hw/boards.h" /* Arbitrary limit on size of each discard command, * keeps them around ~200 bytes */ #define MAX_DISCARDS_PER_COMMAND 12 struct PostcopyDiscardState { const char *ramblock_name; uint16_t cur_entry; /* * Start and length of a discard range (bytes) */ uint64_t start_list[MAX_DISCARDS_PER_COMMAND]; uint64_t length_list[MAX_DISCARDS_PER_COMMAND]; unsigned int nsentwords; unsigned int nsentcmds; }; static NotifierWithReturnList postcopy_notifier_list; void postcopy_infrastructure_init(void) { notifier_with_return_list_init(&postcopy_notifier_list); } void postcopy_add_notifier(NotifierWithReturn *nn) { notifier_with_return_list_add(&postcopy_notifier_list, nn); } void postcopy_remove_notifier(NotifierWithReturn *n) { notifier_with_return_remove(n); } int postcopy_notify(enum PostcopyNotifyReason reason, Error **errp) { struct PostcopyNotifyData pnd; pnd.reason = reason; pnd.errp = errp; return notifier_with_return_list_notify(&postcopy_notifier_list, &pnd); } /* Postcopy needs to detect accesses to pages that haven't yet been copied * across, and efficiently map new pages in, the techniques for doing this * are target OS specific. */ #if defined(__linux__) #include #include #include #include /* for __u64 */ #endif #if defined(__linux__) && defined(__NR_userfaultfd) && defined(CONFIG_EVENTFD) #include #include typedef struct PostcopyBlocktimeContext { /* time when page fault initiated per vCPU */ uint32_t *page_fault_vcpu_time; /* page address per vCPU */ uintptr_t *vcpu_addr; uint32_t total_blocktime; /* blocktime per vCPU */ uint32_t *vcpu_blocktime; /* point in time when last page fault was initiated */ uint32_t last_begin; /* number of vCPU are suspended */ int smp_cpus_down; uint64_t start_time; /* * Handler for exit event, necessary for * releasing whole blocktime_ctx */ Notifier exit_notifier; } PostcopyBlocktimeContext; static void destroy_blocktime_context(struct PostcopyBlocktimeContext *ctx) { g_free(ctx->page_fault_vcpu_time); g_free(ctx->vcpu_addr); g_free(ctx->vcpu_blocktime); g_free(ctx); } static void migration_exit_cb(Notifier *n, void *data) { PostcopyBlocktimeContext *ctx = container_of(n, PostcopyBlocktimeContext, exit_notifier); destroy_blocktime_context(ctx); } static struct PostcopyBlocktimeContext *blocktime_context_new(void) { MachineState *ms = MACHINE(qdev_get_machine()); unsigned int smp_cpus = ms->smp.cpus; PostcopyBlocktimeContext *ctx = g_new0(PostcopyBlocktimeContext, 1); ctx->page_fault_vcpu_time = g_new0(uint32_t, smp_cpus); ctx->vcpu_addr = g_new0(uintptr_t, smp_cpus); ctx->vcpu_blocktime = g_new0(uint32_t, smp_cpus); ctx->exit_notifier.notify = migration_exit_cb; ctx->start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); qemu_add_exit_notifier(&ctx->exit_notifier); return ctx; } static uint32List *get_vcpu_blocktime_list(PostcopyBlocktimeContext *ctx) { MachineState *ms = MACHINE(qdev_get_machine()); uint32List *list = NULL, *entry = NULL; int i; for (i = ms->smp.cpus - 1; i >= 0; i--) { entry = g_new0(uint32List, 1); entry->value = ctx->vcpu_blocktime[i]; entry->next = list; list = entry; } return list; } /* * This function just populates MigrationInfo from postcopy's * blocktime context. It will not populate MigrationInfo, * unless postcopy-blocktime capability was set. * * @info: pointer to MigrationInfo to populate */ void fill_destination_postcopy_migration_info(MigrationInfo *info) { MigrationIncomingState *mis = migration_incoming_get_current(); PostcopyBlocktimeContext *bc = mis->blocktime_ctx; if (!bc) { return; } info->has_postcopy_blocktime = true; info->postcopy_blocktime = bc->total_blocktime; info->has_postcopy_vcpu_blocktime = true; info->postcopy_vcpu_blocktime = get_vcpu_blocktime_list(bc); } static uint32_t get_postcopy_total_blocktime(void) { MigrationIncomingState *mis = migration_incoming_get_current(); PostcopyBlocktimeContext *bc = mis->blocktime_ctx; if (!bc) { return 0; } return bc->total_blocktime; } /** * receive_ufd_features: check userfault fd features, to request only supported * features in the future. * * Returns: true on success * * __NR_userfaultfd - should be checked before * @features: out parameter will contain uffdio_api.features provided by kernel * in case of success */ static bool receive_ufd_features(uint64_t *features) { struct uffdio_api api_struct = {0}; int ufd; bool ret = true; /* if we are here __NR_userfaultfd should exists */ ufd = syscall(__NR_userfaultfd, O_CLOEXEC); if (ufd == -1) { error_report("%s: syscall __NR_userfaultfd failed: %s", __func__, strerror(errno)); return false; } /* ask features */ api_struct.api = UFFD_API; api_struct.features = 0; if (ioctl(ufd, UFFDIO_API, &api_struct)) { error_report("%s: UFFDIO_API failed: %s", __func__, strerror(errno)); ret = false; goto release_ufd; } *features = api_struct.features; release_ufd: close(ufd); return ret; } /** * request_ufd_features: this function should be called only once on a newly * opened ufd, subsequent calls will lead to error. * * Returns: true on succes * * @ufd: fd obtained from userfaultfd syscall * @features: bit mask see UFFD_API_FEATURES */ static bool request_ufd_features(int ufd, uint64_t features) { struct uffdio_api api_struct = {0}; uint64_t ioctl_mask; api_struct.api = UFFD_API; api_struct.features = features; if (ioctl(ufd, UFFDIO_API, &api_struct)) { error_report("%s failed: UFFDIO_API failed: %s", __func__, strerror(errno)); return false; } ioctl_mask = (__u64)1 << _UFFDIO_REGISTER | (__u64)1 << _UFFDIO_UNREGISTER; if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) { error_report("Missing userfault features: %" PRIx64, (uint64_t)(~api_struct.ioctls & ioctl_mask)); return false; } return true; } static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis) { uint64_t asked_features = 0; static uint64_t supported_features; /* * it's not possible to * request UFFD_API twice per one fd * userfault fd features is persistent */ if (!supported_features) { if (!receive_ufd_features(&supported_features)) { error_report("%s failed", __func__); return false; } } #ifdef UFFD_FEATURE_THREAD_ID if (migrate_postcopy_blocktime() && mis && UFFD_FEATURE_THREAD_ID & supported_features) { /* kernel supports that feature */ /* don't create blocktime_context if it exists */ if (!mis->blocktime_ctx) { mis->blocktime_ctx = blocktime_context_new(); } asked_features |= UFFD_FEATURE_THREAD_ID; } #endif /* * request features, even if asked_features is 0, due to * kernel expects UFFD_API before UFFDIO_REGISTER, per * userfault file descriptor */ if (!request_ufd_features(ufd, asked_features)) { error_report("%s failed: features %" PRIu64, __func__, asked_features); return false; } if (getpagesize() != ram_pagesize_summary()) { bool have_hp = false; /* We've got a huge page */ #ifdef UFFD_FEATURE_MISSING_HUGETLBFS have_hp = supported_features & UFFD_FEATURE_MISSING_HUGETLBFS; #endif if (!have_hp) { error_report("Userfault on this host does not support huge pages"); return false; } } return true; } /* Callback from postcopy_ram_supported_by_host block iterator. */ static int test_ramblock_postcopiable(RAMBlock *rb, void *opaque) { const char *block_name = qemu_ram_get_idstr(rb); ram_addr_t length = qemu_ram_get_used_length(rb); size_t pagesize = qemu_ram_pagesize(rb); if (length % pagesize) { error_report("Postcopy requires RAM blocks to be a page size multiple," " block %s is 0x" RAM_ADDR_FMT " bytes with a " "page size of 0x%zx", block_name, length, pagesize); return 1; } return 0; } /* * Note: This has the side effect of munlock'ing all of RAM, that's * normally fine since if the postcopy succeeds it gets turned back on at the * end. */ bool postcopy_ram_supported_by_host(MigrationIncomingState *mis) { long pagesize = getpagesize(); int ufd = -1; bool ret = false; /* Error unless we change it */ void *testarea = NULL; struct uffdio_register reg_struct; struct uffdio_range range_struct; uint64_t feature_mask; Error *local_err = NULL; if (qemu_target_page_size() > pagesize) { error_report("Target page size bigger than host page size"); goto out; } ufd = syscall(__NR_userfaultfd, O_CLOEXEC); if (ufd == -1) { error_report("%s: userfaultfd not available: %s", __func__, strerror(errno)); goto out; } /* Give devices a chance to object */ if (postcopy_notify(POSTCOPY_NOTIFY_PROBE, &local_err)) { error_report_err(local_err); goto out; } /* Version and features check */ if (!ufd_check_and_apply(ufd, mis)) { goto out; } /* We don't support postcopy with shared RAM yet */ if (foreach_not_ignored_block(test_ramblock_postcopiable, NULL)) { goto out; } /* * userfault and mlock don't go together; we'll put it back later if * it was enabled. */ if (munlockall()) { error_report("%s: munlockall: %s", __func__, strerror(errno)); return -1; } /* * We need to check that the ops we need are supported on anon memory * To do that we need to register a chunk and see the flags that * are returned. */ testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (testarea == MAP_FAILED) { error_report("%s: Failed to map test area: %s", __func__, strerror(errno)); goto out; } g_assert(((size_t)testarea & (pagesize-1)) == 0); reg_struct.range.start = (uintptr_t)testarea; reg_struct.range.len = pagesize; reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; if (ioctl(ufd, UFFDIO_REGISTER, ®_struct)) { error_report("%s userfault register: %s", __func__, strerror(errno)); goto out; } range_struct.start = (uintptr_t)testarea; range_struct.len = pagesize; if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) { error_report("%s userfault unregister: %s", __func__, strerror(errno)); goto out; } feature_mask = (__u64)1 << _UFFDIO_WAKE | (__u64)1 << _UFFDIO_COPY | (__u64)1 << _UFFDIO_ZEROPAGE; if ((reg_struct.ioctls & feature_mask) != feature_mask) { error_report("Missing userfault map features: %" PRIx64, (uint64_t)(~reg_struct.ioctls & feature_mask)); goto out; } /* Success! */ ret = true; out: if (testarea) { munmap(testarea, pagesize); } if (ufd != -1) { close(ufd); } return ret; } /* * Setup an area of RAM so that it *can* be used for postcopy later; this * must be done right at the start prior to pre-copy. * opaque should be the MIS. */ static int init_range(RAMBlock *rb, void *opaque) { const char *block_name = qemu_ram_get_idstr(rb); void *host_addr = qemu_ram_get_host_addr(rb); ram_addr_t offset = qemu_ram_get_offset(rb); ram_addr_t length = qemu_ram_get_used_length(rb); trace_postcopy_init_range(block_name, host_addr, offset, length); /* * We need the whole of RAM to be truly empty for postcopy, so things * like ROMs and any data tables built during init must be zero'd * - we're going to get the copy from the source anyway. * (Precopy will just overwrite this data, so doesn't need the discard) */ if (ram_discard_range(block_name, 0, length)) { return -1; } return 0; } /* * At the end of migration, undo the effects of init_range * opaque should be the MIS. */ static int cleanup_range(RAMBlock *rb, void *opaque) { const char *block_name = qemu_ram_get_idstr(rb); void *host_addr = qemu_ram_get_host_addr(rb); ram_addr_t offset = qemu_ram_get_offset(rb); ram_addr_t length = qemu_ram_get_used_length(rb); MigrationIncomingState *mis = opaque; struct uffdio_range range_struct; trace_postcopy_cleanup_range(block_name, host_addr, offset, length); /* * We turned off hugepage for the precopy stage with postcopy enabled * we can turn it back on now. */ qemu_madvise(host_addr, length, QEMU_MADV_HUGEPAGE); /* * We can also turn off userfault now since we should have all the * pages. It can be useful to leave it on to debug postcopy * if you're not sure it's always getting every page. */ range_struct.start = (uintptr_t)host_addr; range_struct.len = length; if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) { error_report("%s: userfault unregister %s", __func__, strerror(errno)); return -1; } return 0; } /* * Initialise postcopy-ram, setting the RAM to a state where we can go into * postcopy later; must be called prior to any precopy. * called from arch_init's similarly named ram_postcopy_incoming_init */ int postcopy_ram_incoming_init(MigrationIncomingState *mis) { if (foreach_not_ignored_block(init_range, NULL)) { return -1; } return 0; } /* * Manage a single vote to the QEMU balloon inhibitor for all postcopy usage, * last caller wins. */ static void postcopy_balloon_inhibit(bool state) { static bool cur_state = false; if (state != cur_state) { qemu_balloon_inhibit(state); cur_state = state; } } /* * At the end of a migration where postcopy_ram_incoming_init was called. */ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) { trace_postcopy_ram_incoming_cleanup_entry(); if (mis->have_fault_thread) { Error *local_err = NULL; /* Let the fault thread quit */ atomic_set(&mis->fault_thread_quit, 1); postcopy_fault_thread_notify(mis); trace_postcopy_ram_incoming_cleanup_join(); qemu_thread_join(&mis->fault_thread); if (postcopy_notify(POSTCOPY_NOTIFY_INBOUND_END, &local_err)) { error_report_err(local_err); return -1; } if (foreach_not_ignored_block(cleanup_range, mis)) { return -1; } trace_postcopy_ram_incoming_cleanup_closeuf(); close(mis->userfault_fd); close(mis->userfault_event_fd); mis->have_fault_thread = false; } postcopy_balloon_inhibit(false); if (enable_mlock) { if (os_mlock() < 0) { error_report("mlock: %s", strerror(errno)); /* * It doesn't feel right to fail at this point, we have a valid * VM state. */ } } if (mis->postcopy_tmp_page) { munmap(mis->postcopy_tmp_page, mis->largest_page_size); mis->postcopy_tmp_page = NULL; } if (mis->postcopy_tmp_zero_page) { munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size); mis->postcopy_tmp_zero_page = NULL; } trace_postcopy_ram_incoming_cleanup_blocktime( get_postcopy_total_blocktime()); trace_postcopy_ram_incoming_cleanup_exit(); return 0; } /* * Disable huge pages on an area */ static int nhp_range(RAMBlock *rb, void *opaque) { const char *block_name = qemu_ram_get_idstr(rb); void *host_addr = qemu_ram_get_host_addr(rb); ram_addr_t offset = qemu_ram_get_offset(rb); ram_addr_t length = qemu_ram_get_used_length(rb); trace_postcopy_nhp_range(block_name, host_addr, offset, length); /* * Before we do discards we need to ensure those discards really * do delete areas of the page, even if THP thinks a hugepage would * be a good idea, so force hugepages off. */ qemu_madvise(host_addr, length, QEMU_MADV_NOHUGEPAGE); return 0; } /* * Userfault requires us to mark RAM as NOHUGEPAGE prior to discard * however leaving it until after precopy means that most of the precopy * data is still THPd */ int postcopy_ram_prepare_discard(MigrationIncomingState *mis) { if (foreach_not_ignored_block(nhp_range, mis)) { return -1; } postcopy_state_set(POSTCOPY_INCOMING_DISCARD); return 0; } /* * Mark the given area of RAM as requiring notification to unwritten areas * Used as a callback on foreach_not_ignored_block. * host_addr: Base of area to mark * offset: Offset in the whole ram arena * length: Length of the section * opaque: MigrationIncomingState pointer * Returns 0 on success */ static int ram_block_enable_notify(RAMBlock *rb, void *opaque) { MigrationIncomingState *mis = opaque; struct uffdio_register reg_struct; reg_struct.range.start = (uintptr_t)qemu_ram_get_host_addr(rb); reg_struct.range.len = qemu_ram_get_used_length(rb); reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING; /* Now tell our userfault_fd that it's responsible for this area */ if (ioctl(mis->userfault_fd, UFFDIO_REGISTER, ®_struct)) { error_report("%s userfault register: %s", __func__, strerror(errno)); return -1; } if (!(reg_struct.ioctls & ((__u64)1 << _UFFDIO_COPY))) { error_report("%s userfault: Region doesn't support COPY", __func__); return -1; } if (reg_struct.ioctls & ((__u64)1 << _UFFDIO_ZEROPAGE)) { qemu_ram_set_uf_zeroable(rb); } return 0; } int postcopy_wake_shared(struct PostCopyFD *pcfd, uint64_t client_addr, RAMBlock *rb) { size_t pagesize = qemu_ram_pagesize(rb); struct uffdio_range range; int ret; trace_postcopy_wake_shared(client_addr, qemu_ram_get_idstr(rb)); range.start = client_addr & ~(pagesize - 1); range.len = pagesize; ret = ioctl(pcfd->fd, UFFDIO_WAKE, &range); if (ret) { error_report("%s: Failed to wake: %zx in %s (%s)", __func__, (size_t)client_addr, qemu_ram_get_idstr(rb), strerror(errno)); } return ret; } /* * Callback from shared fault handlers to ask for a page, * the page must be specified by a RAMBlock and an offset in that rb * Note: Only for use by shared fault handlers (in fault thread) */ int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb, uint64_t client_addr, uint64_t rb_offset) { size_t pagesize = qemu_ram_pagesize(rb); uint64_t aligned_rbo = rb_offset & ~(pagesize - 1); MigrationIncomingState *mis = migration_incoming_get_current(); trace_postcopy_request_shared_page(pcfd->idstr, qemu_ram_get_idstr(rb), rb_offset); if (ramblock_recv_bitmap_test_byte_offset(rb, aligned_rbo)) { trace_postcopy_request_shared_page_present(pcfd->idstr, qemu_ram_get_idstr(rb), rb_offset); return postcopy_wake_shared(pcfd, client_addr, rb); } if (rb != mis->last_rb) { mis->last_rb = rb; migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb), aligned_rbo, pagesize); } else { /* Save some space */ migrate_send_rp_req_pages(mis, NULL, aligned_rbo, pagesize); } return 0; } static int get_mem_fault_cpu_index(uint32_t pid) { CPUState *cpu_iter; CPU_FOREACH(cpu_iter) { if (cpu_iter->thread_id == pid) { trace_get_mem_fault_cpu_index(cpu_iter->cpu_index, pid); return cpu_iter->cpu_index; } } trace_get_mem_fault_cpu_index(-1, pid); return -1; } static uint32_t get_low_time_offset(PostcopyBlocktimeContext *dc) { int64_t start_time_offset = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - dc->start_time; return start_time_offset < 1 ? 1 : start_time_offset & UINT32_MAX; } /* * This function is being called when pagefault occurs. It * tracks down vCPU blocking time. * * @addr: faulted host virtual address * @ptid: faulted process thread id * @rb: ramblock appropriate to addr */ static void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid, RAMBlock *rb) { int cpu, already_received; MigrationIncomingState *mis = migration_incoming_get_current(); PostcopyBlocktimeContext *dc = mis->blocktime_ctx; uint32_t low_time_offset; if (!dc || ptid == 0) { return; } cpu = get_mem_fault_cpu_index(ptid); if (cpu < 0) { return; } low_time_offset = get_low_time_offset(dc); if (dc->vcpu_addr[cpu] == 0) { atomic_inc(&dc->smp_cpus_down); } atomic_xchg(&dc->last_begin, low_time_offset); atomic_xchg(&dc->page_fault_vcpu_time[cpu], low_time_offset); atomic_xchg(&dc->vcpu_addr[cpu], addr); /* * check it here, not at the beginning of the function, * due to, check could occur early than bitmap_set in * qemu_ufd_copy_ioctl */ already_received = ramblock_recv_bitmap_test(rb, (void *)addr); if (already_received) { atomic_xchg(&dc->vcpu_addr[cpu], 0); atomic_xchg(&dc->page_fault_vcpu_time[cpu], 0); atomic_dec(&dc->smp_cpus_down); } trace_mark_postcopy_blocktime_begin(addr, dc, dc->page_fault_vcpu_time[cpu], cpu, already_received); } /* * This function just provide calculated blocktime per cpu and trace it. * Total blocktime is calculated in mark_postcopy_blocktime_end. * * * Assume we have 3 CPU * * S1 E1 S1 E1 * -----***********------------xxx***************------------------------> CPU1 * * S2 E2 * ------------****************xxx---------------------------------------> CPU2 * * S3 E3 * ------------------------****xxx********-------------------------------> CPU3 * * We have sequence S1,S2,E1,S3,S1,E2,E3,E1 * S2,E1 - doesn't match condition due to sequence S1,S2,E1 doesn't include CPU3 * S3,S1,E2 - sequence includes all CPUs, in this case overlap will be S1,E2 - * it's a part of total blocktime. * S1 - here is last_begin * Legend of the picture is following: * * - means blocktime per vCPU * x - means overlapped blocktime (total blocktime) * * @addr: host virtual address */ static void mark_postcopy_blocktime_end(uintptr_t addr) { MigrationIncomingState *mis = migration_incoming_get_current(); PostcopyBlocktimeContext *dc = mis->blocktime_ctx; MachineState *ms = MACHINE(qdev_get_machine()); unsigned int smp_cpus = ms->smp.cpus; int i, affected_cpu = 0; bool vcpu_total_blocktime = false; uint32_t read_vcpu_time, low_time_offset; if (!dc) { return; } low_time_offset = get_low_time_offset(dc); /* lookup cpu, to clear it, * that algorithm looks straighforward, but it's not * optimal, more optimal algorithm is keeping tree or hash * where key is address value is a list of */ for (i = 0; i < smp_cpus; i++) { uint32_t vcpu_blocktime = 0; read_vcpu_time = atomic_fetch_add(&dc->page_fault_vcpu_time[i], 0); if (atomic_fetch_add(&dc->vcpu_addr[i], 0) != addr || read_vcpu_time == 0) { continue; } atomic_xchg(&dc->vcpu_addr[i], 0); vcpu_blocktime = low_time_offset - read_vcpu_time; affected_cpu += 1; /* we need to know is that mark_postcopy_end was due to * faulted page, another possible case it's prefetched * page and in that case we shouldn't be here */ if (!vcpu_total_blocktime && atomic_fetch_add(&dc->smp_cpus_down, 0) == smp_cpus) { vcpu_total_blocktime = true; } /* continue cycle, due to one page could affect several vCPUs */ dc->vcpu_blocktime[i] += vcpu_blocktime; } atomic_sub(&dc->smp_cpus_down, affected_cpu); if (vcpu_total_blocktime) { dc->total_blocktime += low_time_offset - atomic_fetch_add( &dc->last_begin, 0); } trace_mark_postcopy_blocktime_end(addr, dc, dc->total_blocktime, affected_cpu); } static bool postcopy_pause_fault_thread(MigrationIncomingState *mis) { trace_postcopy_pause_fault_thread(); qemu_sem_wait(&mis->postcopy_pause_sem_fault); trace_postcopy_pause_fault_thread_continued(); return true; } /* * Handle faults detected by the USERFAULT markings */ static void *postcopy_ram_fault_thread(void *opaque) { MigrationIncomingState *mis = opaque; struct uffd_msg msg; int ret; size_t index; RAMBlock *rb = NULL; trace_postcopy_ram_fault_thread_entry(); rcu_register_thread(); mis->last_rb = NULL; /* last RAMBlock we sent part of */ qemu_sem_post(&mis->fault_thread_sem); struct pollfd *pfd; size_t pfd_len = 2 + mis->postcopy_remote_fds->len; pfd = g_new0(struct pollfd, pfd_len); pfd[0].fd = mis->userfault_fd; pfd[0].events = POLLIN; pfd[1].fd = mis->userfault_event_fd; pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */ trace_postcopy_ram_fault_thread_fds_core(pfd[0].fd, pfd[1].fd); for (index = 0; index < mis->postcopy_remote_fds->len; index++) { struct PostCopyFD *pcfd = &g_array_index(mis->postcopy_remote_fds, struct PostCopyFD, index); pfd[2 + index].fd = pcfd->fd; pfd[2 + index].events = POLLIN; trace_postcopy_ram_fault_thread_fds_extra(2 + index, pcfd->idstr, pcfd->fd); } while (true) { ram_addr_t rb_offset; int poll_result; /* * We're mainly waiting for the kernel to give us a faulting HVA, * however we can be told to quit via userfault_quit_fd which is * an eventfd */ poll_result = poll(pfd, pfd_len, -1 /* Wait forever */); if (poll_result == -1) { error_report("%s: userfault poll: %s", __func__, strerror(errno)); break; } if (!mis->to_src_file) { /* * Possibly someone tells us that the return path is * broken already using the event. We should hold until * the channel is rebuilt. */ if (postcopy_pause_fault_thread(mis)) { mis->last_rb = NULL; /* Continue to read the userfaultfd */ } else { error_report("%s: paused but don't allow to continue", __func__); break; } } if (pfd[1].revents) { uint64_t tmp64 = 0; /* Consume the signal */ if (read(mis->userfault_event_fd, &tmp64, 8) != 8) { /* Nothing obviously nicer than posting this error. */ error_report("%s: read() failed", __func__); } if (atomic_read(&mis->fault_thread_quit)) { trace_postcopy_ram_fault_thread_quit(); break; } } if (pfd[0].revents) { poll_result--; ret = read(mis->userfault_fd, &msg, sizeof(msg)); if (ret != sizeof(msg)) { if (errno == EAGAIN) { /* * if a wake up happens on the other thread just after * the poll, there is nothing to read. */ continue; } if (ret < 0) { error_report("%s: Failed to read full userfault " "message: %s", __func__, strerror(errno)); break; } else { error_report("%s: Read %d bytes from userfaultfd " "expected %zd", __func__, ret, sizeof(msg)); break; /* Lost alignment, don't know what we'd read next */ } } if (msg.event != UFFD_EVENT_PAGEFAULT) { error_report("%s: Read unexpected event %ud from userfaultfd", __func__, msg.event); continue; /* It's not a page fault, shouldn't happen */ } rb = qemu_ram_block_from_host( (void *)(uintptr_t)msg.arg.pagefault.address, true, &rb_offset); if (!rb) { error_report("postcopy_ram_fault_thread: Fault outside guest: %" PRIx64, (uint64_t)msg.arg.pagefault.address); break; } rb_offset &= ~(qemu_ram_pagesize(rb) - 1); trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address, qemu_ram_get_idstr(rb), rb_offset, msg.arg.pagefault.feat.ptid); mark_postcopy_blocktime_begin( (uintptr_t)(msg.arg.pagefault.address), msg.arg.pagefault.feat.ptid, rb); retry: /* * Send the request to the source - we want to request one * of our host page sizes (which is >= TPS) */ if (rb != mis->last_rb) { mis->last_rb = rb; ret = migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb), rb_offset, qemu_ram_pagesize(rb)); } else { /* Save some space */ ret = migrate_send_rp_req_pages(mis, NULL, rb_offset, qemu_ram_pagesize(rb)); } if (ret) { /* May be network failure, try to wait for recovery */ if (ret == -EIO && postcopy_pause_fault_thread(mis)) { /* We got reconnected somehow, try to continue */ mis->last_rb = NULL; goto retry; } else { /* This is a unavoidable fault */ error_report("%s: migrate_send_rp_req_pages() get %d", __func__, ret); break; } } } /* Now handle any requests from external processes on shared memory */ /* TODO: May need to handle devices deregistering during postcopy */ for (index = 2; index < pfd_len && poll_result; index++) { if (pfd[index].revents) { struct PostCopyFD *pcfd = &g_array_index(mis->postcopy_remote_fds, struct PostCopyFD, index - 2); poll_result--; if (pfd[index].revents & POLLERR) { error_report("%s: POLLERR on poll %zd fd=%d", __func__, index, pcfd->fd); pfd[index].events = 0; continue; } ret = read(pcfd->fd, &msg, sizeof(msg)); if (ret != sizeof(msg)) { if (errno == EAGAIN) { /* * if a wake up happens on the other thread just after * the poll, there is nothing to read. */ continue; } if (ret < 0) { error_report("%s: Failed to read full userfault " "message: %s (shared) revents=%d", __func__, strerror(errno), pfd[index].revents); /*TODO: Could just disable this sharer */ break; } else { error_report("%s: Read %d bytes from userfaultfd " "expected %zd (shared)", __func__, ret, sizeof(msg)); /*TODO: Could just disable this sharer */ break; /*Lost alignment,don't know what we'd read next*/ } } if (msg.event != UFFD_EVENT_PAGEFAULT) { error_report("%s: Read unexpected event %ud " "from userfaultfd (shared)", __func__, msg.event); continue; /* It's not a page fault, shouldn't happen */ } /* Call the device handler registered with us */ ret = pcfd->handler(pcfd, &msg); if (ret) { error_report("%s: Failed to resolve shared fault on %zd/%s", __func__, index, pcfd->idstr); /* TODO: Fail? Disable this sharer? */ } } } } rcu_unregister_thread(); trace_postcopy_ram_fault_thread_exit(); g_free(pfd); return NULL; } int postcopy_ram_incoming_setup(MigrationIncomingState *mis) { /* Open the fd for the kernel to give us userfaults */ mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); if (mis->userfault_fd == -1) { error_report("%s: Failed to open userfault fd: %s", __func__, strerror(errno)); return -1; } /* * Although the host check already tested the API, we need to * do the check again as an ABI handshake on the new fd. */ if (!ufd_check_and_apply(mis->userfault_fd, mis)) { return -1; } /* Now an eventfd we use to tell the fault-thread to quit */ mis->userfault_event_fd = eventfd(0, EFD_CLOEXEC); if (mis->userfault_event_fd == -1) { error_report("%s: Opening userfault_event_fd: %s", __func__, strerror(errno)); close(mis->userfault_fd); return -1; } qemu_sem_init(&mis->fault_thread_sem, 0); qemu_thread_create(&mis->fault_thread, "postcopy/fault", postcopy_ram_fault_thread, mis, QEMU_THREAD_JOINABLE); qemu_sem_wait(&mis->fault_thread_sem); qemu_sem_destroy(&mis->fault_thread_sem); mis->have_fault_thread = true; /* Mark so that we get notified of accesses to unwritten areas */ if (foreach_not_ignored_block(ram_block_enable_notify, mis)) { error_report("ram_block_enable_notify failed"); return -1; } mis->postcopy_tmp_page = mmap(NULL, mis->largest_page_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (mis->postcopy_tmp_page == MAP_FAILED) { mis->postcopy_tmp_page = NULL; error_report("%s: Failed to map postcopy_tmp_page %s", __func__, strerror(errno)); return -1; } /* * Map large zero page when kernel can't use UFFDIO_ZEROPAGE for hugepages */ mis->postcopy_tmp_zero_page = mmap(NULL, mis->largest_page_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (mis->postcopy_tmp_zero_page == MAP_FAILED) { int e = errno; mis->postcopy_tmp_zero_page = NULL; error_report("%s: Failed to map large zero page %s", __func__, strerror(e)); return -e; } memset(mis->postcopy_tmp_zero_page, '\0', mis->largest_page_size); /* * Ballooning can mark pages as absent while we're postcopying * that would cause false userfaults. */ postcopy_balloon_inhibit(true); trace_postcopy_ram_enable_notify(); return 0; } static int qemu_ufd_copy_ioctl(int userfault_fd, void *host_addr, void *from_addr, uint64_t pagesize, RAMBlock *rb) { int ret; if (from_addr) { struct uffdio_copy copy_struct; copy_struct.dst = (uint64_t)(uintptr_t)host_addr; copy_struct.src = (uint64_t)(uintptr_t)from_addr; copy_struct.len = pagesize; copy_struct.mode = 0; ret = ioctl(userfault_fd, UFFDIO_COPY, ©_struct); } else { struct uffdio_zeropage zero_struct; zero_struct.range.start = (uint64_t)(uintptr_t)host_addr; zero_struct.range.len = pagesize; zero_struct.mode = 0; ret = ioctl(userfault_fd, UFFDIO_ZEROPAGE, &zero_struct); } if (!ret) { ramblock_recv_bitmap_set_range(rb, host_addr, pagesize / qemu_target_page_size()); mark_postcopy_blocktime_end((uintptr_t)host_addr); } return ret; } int postcopy_notify_shared_wake(RAMBlock *rb, uint64_t offset) { int i; MigrationIncomingState *mis = migration_incoming_get_current(); GArray *pcrfds = mis->postcopy_remote_fds; for (i = 0; i < pcrfds->len; i++) { struct PostCopyFD *cur = &g_array_index(pcrfds, struct PostCopyFD, i); int ret = cur->waker(cur, rb, offset); if (ret) { return ret; } } return 0; } /* * Place a host page (from) at (host) atomically * returns 0 on success */ int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from, RAMBlock *rb) { size_t pagesize = qemu_ram_pagesize(rb); /* copy also acks to the kernel waking the stalled thread up * TODO: We can inhibit that ack and only do it if it was requested * which would be slightly cheaper, but we'd have to be careful * of the order of updating our page state. */ if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, from, pagesize, rb)) { int e = errno; error_report("%s: %s copy host: %p from: %p (size: %zd)", __func__, strerror(e), host, from, pagesize); return -e; } trace_postcopy_place_page(host); return postcopy_notify_shared_wake(rb, qemu_ram_block_host_offset(rb, host)); } /* * Place a zero page at (host) atomically * returns 0 on success */ int postcopy_place_page_zero(MigrationIncomingState *mis, void *host, RAMBlock *rb) { size_t pagesize = qemu_ram_pagesize(rb); trace_postcopy_place_page_zero(host); /* Normal RAMBlocks can zero a page using UFFDIO_ZEROPAGE * but it's not available for everything (e.g. hugetlbpages) */ if (qemu_ram_is_uf_zeroable(rb)) { if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, NULL, pagesize, rb)) { int e = errno; error_report("%s: %s zero host: %p", __func__, strerror(e), host); return -e; } return postcopy_notify_shared_wake(rb, qemu_ram_block_host_offset(rb, host)); } else { return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page, rb); } } #else /* No target OS support, stubs just fail */ void fill_destination_postcopy_migration_info(MigrationInfo *info) { } bool postcopy_ram_supported_by_host(MigrationIncomingState *mis) { error_report("%s: No OS support", __func__); return false; } int postcopy_ram_incoming_init(MigrationIncomingState *mis) { error_report("postcopy_ram_incoming_init: No OS support"); return -1; } int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) { assert(0); return -1; } int postcopy_ram_prepare_discard(MigrationIncomingState *mis) { assert(0); return -1; } int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb, uint64_t client_addr, uint64_t rb_offset) { assert(0); return -1; } int postcopy_ram_incoming_setup(MigrationIncomingState *mis) { assert(0); return -1; } int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from, RAMBlock *rb) { assert(0); return -1; } int postcopy_place_page_zero(MigrationIncomingState *mis, void *host, RAMBlock *rb) { assert(0); return -1; } int postcopy_wake_shared(struct PostCopyFD *pcfd, uint64_t client_addr, RAMBlock *rb) { assert(0); return -1; } #endif /* ------------------------------------------------------------------------- */ void postcopy_fault_thread_notify(MigrationIncomingState *mis) { uint64_t tmp64 = 1; /* * Wakeup the fault_thread. It's an eventfd that should currently * be at 0, we're going to increment it to 1 */ if (write(mis->userfault_event_fd, &tmp64, 8) != 8) { /* Not much we can do here, but may as well report it */ error_report("%s: incrementing failed: %s", __func__, strerror(errno)); } } /** * postcopy_discard_send_init: Called at the start of each RAMBlock before * asking to discard individual ranges. * * @ms: The current migration state. * @offset: the bitmap offset of the named RAMBlock in the migration bitmap. * @name: RAMBlock that discards will operate on. */ static PostcopyDiscardState pds = {0}; void postcopy_discard_send_init(MigrationState *ms, const char *name) { pds.ramblock_name = name; pds.cur_entry = 0; pds.nsentwords = 0; pds.nsentcmds = 0; } /** * postcopy_discard_send_range: Called by the bitmap code for each chunk to * discard. May send a discard message, may just leave it queued to * be sent later. * * @ms: Current migration state. * @start,@length: a range of pages in the migration bitmap in the * RAM block passed to postcopy_discard_send_init() (length=1 is one page) */ void postcopy_discard_send_range(MigrationState *ms, unsigned long start, unsigned long length) { size_t tp_size = qemu_target_page_size(); /* Convert to byte offsets within the RAM block */ pds.start_list[pds.cur_entry] = start * tp_size; pds.length_list[pds.cur_entry] = length * tp_size; trace_postcopy_discard_send_range(pds.ramblock_name, start, length); pds.cur_entry++; pds.nsentwords++; if (pds.cur_entry == MAX_DISCARDS_PER_COMMAND) { /* Full set, ship it! */ qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file, pds.ramblock_name, pds.cur_entry, pds.start_list, pds.length_list); pds.nsentcmds++; pds.cur_entry = 0; } } /** * postcopy_discard_send_finish: Called at the end of each RAMBlock by the * bitmap code. Sends any outstanding discard messages, frees the PDS * * @ms: Current migration state. */ void postcopy_discard_send_finish(MigrationState *ms) { /* Anything unsent? */ if (pds.cur_entry) { qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file, pds.ramblock_name, pds.cur_entry, pds.start_list, pds.length_list); pds.nsentcmds++; } trace_postcopy_discard_send_finish(pds.ramblock_name, pds.nsentwords, pds.nsentcmds); } /* * Current state of incoming postcopy; note this is not part of * MigrationIncomingState since it's state is used during cleanup * at the end as MIS is being freed. */ static PostcopyState incoming_postcopy_state; PostcopyState postcopy_state_get(void) { return atomic_mb_read(&incoming_postcopy_state); } /* Set the state and return the old state */ PostcopyState postcopy_state_set(PostcopyState new_state) { return atomic_xchg(&incoming_postcopy_state, new_state); } /* Register a handler for external shared memory postcopy * called on the destination. */ void postcopy_register_shared_ufd(struct PostCopyFD *pcfd) { MigrationIncomingState *mis = migration_incoming_get_current(); mis->postcopy_remote_fds = g_array_append_val(mis->postcopy_remote_fds, *pcfd); } /* Unregister a handler for external shared memory postcopy */ void postcopy_unregister_shared_ufd(struct PostCopyFD *pcfd) { guint i; MigrationIncomingState *mis = migration_incoming_get_current(); GArray *pcrfds = mis->postcopy_remote_fds; for (i = 0; i < pcrfds->len; i++) { struct PostCopyFD *cur = &g_array_index(pcrfds, struct PostCopyFD, i); if (cur->fd == pcfd->fd) { mis->postcopy_remote_fds = g_array_remove_index(pcrfds, i); return; } } }