/* * 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 "qemu-common.h" #include "exec/target_page.h" #include "migration/migration.h" #include "migration/qemu-file.h" #include "savevm.h" #include "postcopy-ram.h" #include "sysemu/sysemu.h" #include "sysemu/balloon.h" #include "qemu/error-report.h" #include "trace.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; }; /* 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 static bool ufd_version_check(int ufd) { struct uffdio_api api_struct; uint64_t ioctl_mask; api_struct.api = UFFD_API; api_struct.features = 0; if (ioctl(ufd, UFFDIO_API, &api_struct)) { error_report("postcopy_ram_supported_by_host: UFFDIO_API failed: %s", 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; } if (getpagesize() != ram_pagesize_summary()) { bool have_hp = false; /* We've got a huge page */ #ifdef UFFD_FEATURE_MISSING_HUGETLBFS have_hp = api_struct.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(const char *block_name, void *host_addr, ram_addr_t offset, ram_addr_t length, void *opaque) { RAMBlock *rb = qemu_ram_block_by_name(block_name); size_t pagesize = qemu_ram_pagesize(rb); if (qemu_ram_is_shared(rb)) { error_report("Postcopy on shared RAM (%s) is not yet supported", block_name); return 1; } 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(void) { 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; 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; } /* Version and features check */ if (!ufd_version_check(ufd)) { goto out; } /* We don't support postcopy with shared RAM yet */ if (qemu_ram_foreach_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(const char *block_name, void *host_addr, ram_addr_t offset, ram_addr_t length, void *opaque) { 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(const char *block_name, void *host_addr, ram_addr_t offset, ram_addr_t length, void *opaque) { 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, size_t ram_pages) { if (qemu_ram_foreach_block(init_range, NULL)) { return -1; } return 0; } /* * 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) { uint64_t tmp64; if (qemu_ram_foreach_block(cleanup_range, mis)) { return -1; } /* * Tell the fault_thread to exit, it's an eventfd that should * currently be at 0, we're going to increment it to 1 */ tmp64 = 1; if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) { trace_postcopy_ram_incoming_cleanup_join(); qemu_thread_join(&mis->fault_thread); } else { /* Not much we can do here, but may as well report it */ error_report("%s: incrementing userfault_quit_fd: %s", __func__, strerror(errno)); } trace_postcopy_ram_incoming_cleanup_closeuf(); close(mis->userfault_fd); close(mis->userfault_quit_fd); mis->have_fault_thread = false; } qemu_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. */ } } postcopy_state_set(POSTCOPY_INCOMING_END); migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0); 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_exit(); return 0; } /* * Disable huge pages on an area */ static int nhp_range(const char *block_name, void *host_addr, ram_addr_t offset, ram_addr_t length, void *opaque) { 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 (qemu_ram_foreach_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 qemu_ram_foreach_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(const char *block_name, void *host_addr, ram_addr_t offset, ram_addr_t length, void *opaque) { MigrationIncomingState *mis = opaque; struct uffdio_register reg_struct; reg_struct.range.start = (uintptr_t)host_addr; reg_struct.range.len = length; 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; } return 0; } /* * Handle faults detected by the USERFAULT markings */ static void *postcopy_ram_fault_thread(void *opaque) { MigrationIncomingState *mis = opaque; struct uffd_msg msg; int ret; RAMBlock *rb = NULL; RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */ trace_postcopy_ram_fault_thread_entry(); qemu_sem_post(&mis->fault_thread_sem); while (true) { ram_addr_t rb_offset; struct pollfd pfd[2]; /* * 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 */ pfd[0].fd = mis->userfault_fd; pfd[0].events = POLLIN; pfd[0].revents = 0; pfd[1].fd = mis->userfault_quit_fd; pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */ pfd[1].revents = 0; if (poll(pfd, 2, -1 /* Wait forever */) == -1) { error_report("%s: userfault poll: %s", __func__, strerror(errno)); break; } if (pfd[1].revents) { trace_postcopy_ram_fault_thread_quit(); break; } 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); /* * Send the request to the source - we want to request one * of our host page sizes (which is >= TPS) */ if (rb != last_rb) { last_rb = rb; migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb), rb_offset, qemu_ram_pagesize(rb)); } else { /* Save some space */ migrate_send_rp_req_pages(mis, NULL, rb_offset, qemu_ram_pagesize(rb)); } } trace_postcopy_ram_fault_thread_exit(); return NULL; } int postcopy_ram_enable_notify(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_version_check(mis->userfault_fd)) { return -1; } /* Now an eventfd we use to tell the fault-thread to quit */ mis->userfault_quit_fd = eventfd(0, EFD_CLOEXEC); if (mis->userfault_quit_fd == -1) { error_report("%s: Opening userfault_quit_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 (qemu_ram_foreach_block(ram_block_enable_notify, mis)) { return -1; } /* * Ballooning can mark pages as absent while we're postcopying * that would cause false userfaults. */ qemu_balloon_inhibit(true); trace_postcopy_ram_enable_notify(); return 0; } /* * Place a host page (from) at (host) atomically * returns 0 on success */ int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from, size_t pagesize) { struct uffdio_copy copy_struct; copy_struct.dst = (uint64_t)(uintptr_t)host; copy_struct.src = (uint64_t)(uintptr_t)from; copy_struct.len = pagesize; copy_struct.mode = 0; /* 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 (ioctl(mis->userfault_fd, UFFDIO_COPY, ©_struct)) { 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 0; } /* * Place a zero page at (host) atomically * returns 0 on success */ int postcopy_place_page_zero(MigrationIncomingState *mis, void *host, size_t pagesize) { trace_postcopy_place_page_zero(host); if (pagesize == getpagesize()) { struct uffdio_zeropage zero_struct; zero_struct.range.start = (uint64_t)(uintptr_t)host; zero_struct.range.len = getpagesize(); zero_struct.mode = 0; if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) { int e = errno; error_report("%s: %s zero host: %p", __func__, strerror(e), host); return -e; } } else { /* The kernel can't use UFFDIO_ZEROPAGE for hugepages */ if (!mis->postcopy_tmp_zero_page) { 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: %s mapping large zero page", __func__, strerror(e)); return -e; } memset(mis->postcopy_tmp_zero_page, '\0', mis->largest_page_size); } return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page, pagesize); } return 0; } /* * Returns a target page of memory that can be mapped at a later point in time * using postcopy_place_page * The same address is used repeatedly, postcopy_place_page just takes the * backing page away. * Returns: Pointer to allocated page * */ void *postcopy_get_tmp_page(MigrationIncomingState *mis) { if (!mis->postcopy_tmp_page) { 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: %s", __func__, strerror(errno)); return NULL; } } return mis->postcopy_tmp_page; } #else /* No target OS support, stubs just fail */ bool postcopy_ram_supported_by_host(void) { error_report("%s: No OS support", __func__); return false; } int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages) { 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_ram_enable_notify(MigrationIncomingState *mis) { assert(0); return -1; } int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from, size_t pagesize) { assert(0); return -1; } int postcopy_place_page_zero(MigrationIncomingState *mis, void *host, size_t pagesize) { assert(0); return -1; } void *postcopy_get_tmp_page(MigrationIncomingState *mis) { assert(0); return NULL; } #endif /* ------------------------------------------------------------------------- */ /** * 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. * * returns: a new PDS. */ PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms, const char *name) { PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState)); if (res) { res->ramblock_name = name; } return res; } /** * 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. * @pds: Structure initialised by postcopy_discard_send_init(). * @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, PostcopyDiscardState *pds, 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. * @pds: Structure initialised by postcopy_discard_send_init(). */ void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds) { /* 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); g_free(pds); } /* * 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); }