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qemu/migration/postcopy-ram.c
Arun Menon 44cdbaa98e migration: push Error **errp into ram_postcopy_incoming_init() 
This is an incremental step in converting vmstate loading
code to report error via Error objects instead of directly
printing it to console/monitor.
It is ensured that ram_postcopy_incoming_init() must report an error
in errp, in case of failure.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Arun Menon <armenon@redhat.com>
Tested-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Link: https://lore.kernel.org/r/20250918-propagate_tpm_error-v14-14-36f11a6fb9d3@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
2025-10-03 09:48:02 -04:00

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/*
* Postcopy migration for RAM
*
* Copyright 2013-2015 Red Hat, Inc. and/or its affiliates
*
* Authors:
* Dave Gilbert <dgilbert@redhat.com>
*
* 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/madvise.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 "system/system.h"
#include "qemu/error-report.h"
#include "trace.h"
#include "hw/boards.h"
#include "system/ramblock.h"
#include "socket.h"
#include "yank_functions.h"
#include "tls.h"
#include "qemu/userfaultfd.h"
#include "qemu/mmap-alloc.h"
#include "options.h"
/* Arbitrary limit on size of each discard command,
* keeps them around ~200 bytes
*/
#define MAX_DISCARDS_PER_COMMAND 12
typedef 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;
} PostcopyDiscardState;
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;
return notifier_with_return_list_notify(&postcopy_notifier_list,
&pnd, errp);
}
/*
* NOTE: this routine is not thread safe, we can't call it concurrently. But it
* should be good enough for migration's purposes.
*/
void postcopy_thread_create(MigrationIncomingState *mis,
QemuThread *thread, const char *name,
void *(*fn)(void *), int joinable)
{
qemu_event_init(&mis->thread_sync_event, false);
qemu_thread_create(thread, name, fn, mis, joinable);
qemu_event_wait(&mis->thread_sync_event);
qemu_event_destroy(&mis->thread_sync_event);
}
/* 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 <poll.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#endif
#if defined(__linux__) && defined(__NR_userfaultfd) && defined(CONFIG_EVENTFD)
#include <sys/eventfd.h>
#include <linux/userfaultfd.h>
/*
* Here we use 24 buckets, which means the last bucket will cover [2^24 us,
* 2^25 us) ~= [16, 32) seconds. It should be far enough to record even
* extreme (perf-wise broken) 1G pages moving over, which can sometimes
* take a few seconds due to various reasons. Anything more than that
* might be unsensible to account anymore.
*/
#define BLOCKTIME_LATENCY_BUCKET_N (24)
/* All the time records are in unit of nanoseconds */
typedef struct PostcopyBlocktimeContext {
/* blocktime per vCPU */
uint64_t *vcpu_blocktime_total;
/* count of faults per vCPU */
uint64_t *vcpu_faults_count;
/*
* count of currently blocked faults per vCPU.
*
* NOTE: Normally there should only be one fault in-progress per vCPU
* thread, so logically it _seems_ vcpu_faults_count[] for any vCPU
* should be either zero or one. However, there can be reasons we see
* >1 faults on the same vCPU thread.
*
* CASE (1): since the process to resolve faults (ioctl(UFFDIO_COPY),
* for example) is done before taking the mutex that protects the
* blocktime context, it can happen that we read more than one faulted
* addresses per vCPU.
*
* One example when we can see >1 faulted addresses for one vCPU:
*
* vcpu1 thread fault thread resolve thread
* ============ ============ ==============
*
* faulted on addr1
* read uffd msg (addr1)
* MUTEX_LOCK
* add entry (cpu1, addr1)
* MUTEX_UNLOCK
* request remote fault (addr1)
* resolve fault (addr1)
* addr1 resolved, continue..
* faulted on addr2
* read uffd msg (addr2)
* MUTEX_LOCK
* add entry (cpu1, addr2) <--------------- [A]
* MUTEX_UNLOCK
* MUTEX_LOCK
* remove entry (cpu1, addr1)
* MUTEX_UNLOCK
*
* In above case, we may see (cpu1, addr1) and (cpu1, addr2) entries to
* appear together at [A], when it gets the lock before the resolve
* thread. Use this counter to maintain such case, and only when it
* reaches zero we know the vCPU is not blocked anymore.
*
* CASE (2): theoretically (the author admit to not have verified
* this..), one vCPU thread can also generate more than one userfaultfd
* message on the same address. It can happen e.g. for whatever reason
* the fault got retried before a resolution arrives. In that extremely
* rare case, we could also see two (cpu1, addr1) entries.
*
* In all cases, be prepared with such re-entrancies with this array.
*
* Using uint8_t should be far enough for now. For example, when
* there're only one resolve thread (postcopy ram listening thread),
* the max (concurrent fault entries) should be two.
*/
uint8_t *vcpu_faults_current;
/*
* The hash that contains addr1->[(cpu1,ts1),(cpu2,ts2) ...] mappings.
* Each of the entry is a tuple of (CPU index, fault timestamp) showing
* that a fault was requested.
*/
GHashTable *vcpu_addr_hash;
/*
* Each bucket stores the count of faults that were resolved within the
* bucket window [2^N us, 2^(N+1) us).
*/
uint64_t latency_buckets[BLOCKTIME_LATENCY_BUCKET_N];
/* total blocktime when all vCPUs are stopped */
uint64_t total_blocktime;
/* point in time when last page fault was initiated */
uint64_t last_begin;
/* number of vCPU are suspended */
int smp_cpus_down;
/*
* Fast path for looking up vcpu_index from tid. NOTE: this result
* only reflects the vcpu setup when postcopy is running. It may not
* always match with the current vcpu setup because vcpus can be hot
* attached/detached after migration completes. However this should be
* stable when blocktime is using the structure.
*/
GHashTable *tid_to_vcpu_hash;
/* Count of non-vCPU faults. This is only for debugging purpose. */
uint64_t non_vcpu_faults;
/* total blocktime when a non-vCPU thread is stopped */
uint64_t non_vcpu_blocktime_total;
/*
* Handler for exit event, necessary for
* releasing whole blocktime_ctx
*/
Notifier exit_notifier;
} PostcopyBlocktimeContext;
typedef struct {
/* The time the fault was triggered */
uint64_t fault_time;
/*
* The vCPU index that was blocked, when cpu==-1, it means it's a
* fault from non-vCPU threads.
*/
int cpu;
} BlocktimeVCPUEntry;
/* Alloc an entry to record a vCPU fault */
static BlocktimeVCPUEntry *
blocktime_vcpu_entry_alloc(int cpu, uint64_t fault_time)
{
BlocktimeVCPUEntry *entry = g_new(BlocktimeVCPUEntry, 1);
entry->fault_time = fault_time;
entry->cpu = cpu;
return entry;
}
/* Free a @GList of @BlocktimeVCPUEntry */
static void blocktime_vcpu_list_free(gpointer data)
{
g_list_free_full(data, g_free);
}
static void destroy_blocktime_context(struct PostcopyBlocktimeContext *ctx)
{
g_hash_table_destroy(ctx->tid_to_vcpu_hash);
g_hash_table_destroy(ctx->vcpu_addr_hash);
g_free(ctx->vcpu_blocktime_total);
g_free(ctx->vcpu_faults_count);
g_free(ctx->vcpu_faults_current);
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 GHashTable *blocktime_init_tid_to_vcpu_hash(void)
{
/*
* TID as an unsigned int can be directly used as the key. However,
* CPU index can NOT be directly used as value, because CPU index can
* be 0, which means NULL. Then when lookup we can never know whether
* it's 0 or "not found". Hence use an indirection for CPU index.
*/
GHashTable *table = g_hash_table_new_full(g_direct_hash, g_direct_equal,
NULL, g_free);
CPUState *cpu;
/*
* Initialize the tid->cpu_id mapping for lookups. The caller needs to
* make sure when reaching here the CPU topology is frozen and will be
* stable for the whole blocktime trapping period.
*/
CPU_FOREACH(cpu) {
int *value = g_new(int, 1);
*value = cpu->cpu_index;
g_hash_table_insert(table,
GUINT_TO_POINTER((uint32_t)cpu->thread_id),
value);
trace_postcopy_blocktime_tid_cpu_map(cpu->cpu_index, cpu->thread_id);
}
return table;
}
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);
/* Initialize all counters to be zeros */
memset(ctx->latency_buckets, 0, sizeof(ctx->latency_buckets));
ctx->vcpu_blocktime_total = g_new0(uint64_t, smp_cpus);
ctx->vcpu_faults_count = g_new0(uint64_t, smp_cpus);
ctx->vcpu_faults_current = g_new0(uint8_t, smp_cpus);
ctx->tid_to_vcpu_hash = blocktime_init_tid_to_vcpu_hash();
/*
* The key (host virtual addresses) will always be gpointer-sized on
* either 32bits or 64bits systems, so it'll fit as a direct key.
*
* The value will be a list of BlocktimeVCPUEntry entries.
*/
ctx->vcpu_addr_hash = g_hash_table_new_full(g_direct_hash,
g_direct_equal,
NULL,
blocktime_vcpu_list_free);
ctx->exit_notifier.notify = migration_exit_cb;
qemu_add_exit_notifier(&ctx->exit_notifier);
return ctx;
}
/*
* 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;
MachineState *ms = MACHINE(qdev_get_machine());
uint64_t latency_total = 0, faults = 0;
uint32List *list_blocktime = NULL;
uint64List *list_latency = NULL;
uint64List *latency_buckets = NULL;
int i;
if (!bc) {
return;
}
for (i = ms->smp.cpus - 1; i >= 0; i--) {
uint64_t latency, total, count;
/* Convert ns -> ms */
QAPI_LIST_PREPEND(list_blocktime,
(uint32_t)(bc->vcpu_blocktime_total[i] / SCALE_MS));
/* The rest in nanoseconds */
total = bc->vcpu_blocktime_total[i];
latency_total += total;
count = bc->vcpu_faults_count[i];
faults += count;
if (count) {
latency = total / count;
} else {
/* No fault detected */
latency = 0;
}
QAPI_LIST_PREPEND(list_latency, latency);
}
for (i = BLOCKTIME_LATENCY_BUCKET_N - 1; i >= 0; i--) {
QAPI_LIST_PREPEND(latency_buckets, bc->latency_buckets[i]);
}
latency_total += bc->non_vcpu_blocktime_total;
faults += bc->non_vcpu_faults;
info->has_postcopy_non_vcpu_latency = true;
info->postcopy_non_vcpu_latency = bc->non_vcpu_faults ?
(bc->non_vcpu_blocktime_total / bc->non_vcpu_faults) : 0;
info->has_postcopy_blocktime = true;
/* Convert ns -> ms */
info->postcopy_blocktime = (uint32_t)(bc->total_blocktime / SCALE_MS);
info->has_postcopy_vcpu_blocktime = true;
info->postcopy_vcpu_blocktime = list_blocktime;
info->has_postcopy_latency = true;
info->postcopy_latency = faults ? (latency_total / faults) : 0;
info->has_postcopy_vcpu_latency = true;
info->postcopy_vcpu_latency = list_latency;
info->has_postcopy_latency_dist = true;
info->postcopy_latency_dist = latency_buckets;
}
static uint64_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;
ufd = uffd_open(O_CLOEXEC);
if (ufd == -1) {
error_report("%s: uffd_open() 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 success
*
* @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 = 1ULL << _UFFDIO_REGISTER |
1ULL << _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,
Error **errp)
{
ERRP_GUARD();
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_setg(errp, "Userfault feature detection failed");
return false;
}
}
#ifdef UFFD_FEATURE_THREAD_ID
/*
* Postcopy blocktime conditionally needs THREAD_ID feature (introduced
* to Linux in 2017). Always try to enable it when QEMU is compiled
* with such environment.
*/
if (UFFD_FEATURE_THREAD_ID & supported_features) {
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_setg(errp, "Failed features %" PRIu64, asked_features);
return false;
}
if (qemu_real_host_page_size() != 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_setg(errp,
"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, Error **errp)
{
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);
QemuFsType fs;
if (length % pagesize) {
error_setg(errp,
"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;
}
if (rb->fd >= 0) {
fs = qemu_fd_getfs(rb->fd);
if (fs != QEMU_FS_TYPE_TMPFS && fs != QEMU_FS_TYPE_HUGETLBFS) {
error_setg(errp,
"Host backend files need to be TMPFS or HUGETLBFS only");
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, Error **errp)
{
ERRP_GUARD();
long pagesize = qemu_real_host_page_size();
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;
RAMBlock *block;
if (qemu_target_page_size() > pagesize) {
error_setg(errp, "Target page size bigger than host page size");
goto out;
}
ufd = uffd_open(O_CLOEXEC);
if (ufd == -1) {
error_setg(errp, "Userfaultfd not available: %s", strerror(errno));
goto out;
}
/* Give devices a chance to object */
if (postcopy_notify(POSTCOPY_NOTIFY_PROBE, errp)) {
goto out;
}
/* Version and features check */
if (!ufd_check_and_apply(ufd, mis, errp)) {
goto out;
}
/*
* We don't support postcopy with some type of ramblocks.
*
* NOTE: we explicitly ignored migrate_ram_is_ignored() instead we checked
* all possible ramblocks. This is because this function can be called
* when creating the migration object, during the phase RAM_MIGRATABLE
* is not even properly set for all the ramblocks.
*
* A side effect of this is we'll also check against RAM_SHARED
* ramblocks even if migrate_ignore_shared() is set (in which case
* we'll never migrate RAM_SHARED at all), but normally this shouldn't
* affect in reality, or we can revisit.
*/
RAMBLOCK_FOREACH(block) {
if (test_ramblock_postcopiable(block, errp)) {
goto out;
}
}
/*
* userfault and mlock don't go together; we'll put it back later if
* it was enabled.
*/
if (munlockall()) {
error_setg(errp, "munlockall() failed: %s", strerror(errno));
goto out;
}
/*
* 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_setg(errp, "Failed to map test area: %s", strerror(errno));
goto out;
}
g_assert(QEMU_PTR_IS_ALIGNED(testarea, pagesize));
reg_struct.range.start = (uintptr_t)testarea;
reg_struct.range.len = pagesize;
reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
if (ioctl(ufd, UFFDIO_REGISTER, &reg_struct)) {
error_setg(errp, "UFFDIO_REGISTER failed: %s", strerror(errno));
goto out;
}
range_struct.start = (uintptr_t)testarea;
range_struct.len = pagesize;
if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
error_setg(errp, "UFFDIO_UNREGISTER failed: %s", strerror(errno));
goto out;
}
feature_mask = 1ULL << _UFFDIO_WAKE |
1ULL << _UFFDIO_COPY |
1ULL << _UFFDIO_ZEROPAGE;
if ((reg_struct.ioctls & feature_mask) != feature_mask) {
error_setg(errp, "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)
{
Error **errp = 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);
/*
* Save the used_length before running the guest. In case we have to
* resize RAM blocks when syncing RAM block sizes from the source during
* precopy, we'll update it manually via the ram block notifier.
*/
rb->postcopy_length = 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)) {
error_setg(errp, "failed to discard RAM block %s len=%zu",
block_name, 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 = rb->postcopy_length;
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, Error **errp)
{
if (foreach_not_ignored_block(init_range, errp)) {
return -1;
}
return 0;
}
static void postcopy_temp_pages_cleanup(MigrationIncomingState *mis)
{
int i;
if (mis->postcopy_tmp_pages) {
for (i = 0; i < mis->postcopy_channels; i++) {
if (mis->postcopy_tmp_pages[i].tmp_huge_page) {
munmap(mis->postcopy_tmp_pages[i].tmp_huge_page,
mis->largest_page_size);
mis->postcopy_tmp_pages[i].tmp_huge_page = NULL;
}
}
g_free(mis->postcopy_tmp_pages);
mis->postcopy_tmp_pages = NULL;
}
if (mis->postcopy_tmp_zero_page) {
munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size);
mis->postcopy_tmp_zero_page = NULL;
}
}
/*
* 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->preempt_thread_status == PREEMPT_THREAD_CREATED) {
/* Notify the fast load thread to quit */
mis->preempt_thread_status = PREEMPT_THREAD_QUIT;
/*
* Update preempt_thread_status before reading count. Note: mutex
* lock only provide ACQUIRE semantic, and it doesn't stops this
* write to be reordered after reading the count.
*/
smp_mb();
/*
* It's possible that the preempt thread is still handling the last
* pages to arrive which were requested by guest page faults.
* Making sure nothing is left behind by waiting on the condvar if
* that unlikely case happened.
*/
WITH_QEMU_LOCK_GUARD(&mis->page_request_mutex) {
if (qatomic_read(&mis->page_requested_count)) {
/*
* It is guaranteed to receive a signal later, because the
* count>0 now, so it's destined to be decreased to zero
* very soon by the preempt thread.
*/
qemu_cond_wait(&mis->page_request_cond,
&mis->page_request_mutex);
}
}
/* Notify the fast load thread to quit */
if (mis->postcopy_qemufile_dst) {
qemu_file_shutdown(mis->postcopy_qemufile_dst);
}
qemu_thread_join(&mis->postcopy_prio_thread);
mis->preempt_thread_status = PREEMPT_THREAD_NONE;
}
if (mis->have_fault_thread) {
Error *local_err = NULL;
/* Let the fault thread quit */
qatomic_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;
}
if (should_mlock(mlock_state)) {
if (os_mlock(is_mlock_on_fault(mlock_state)) < 0) {
error_report("mlock: %s", strerror(errno));
/*
* It doesn't feel right to fail at this point, we have a valid
* VM state.
*/
}
}
postcopy_temp_pages_cleanup(mis);
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 = rb->postcopy_length;
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 = rb->postcopy_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, &reg_struct)) {
error_report("%s userfault register: %s", __func__, strerror(errno));
return -1;
}
if (!(reg_struct.ioctls & (1ULL << _UFFDIO_COPY))) {
error_report("%s userfault: Region doesn't support COPY", __func__);
return -1;
}
if (reg_struct.ioctls & (1ULL << _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);
trace_postcopy_wake_shared(client_addr, qemu_ram_get_idstr(rb));
return uffd_wakeup(pcfd->fd,
(void *)(uintptr_t)ROUND_DOWN(client_addr, pagesize),
pagesize);
}
/*
* NOTE: @tid is only used when postcopy-blocktime feature is enabled, and
* also optional: when zero is provided, the fault accounting will be ignored.
*/
static int postcopy_request_page(MigrationIncomingState *mis, RAMBlock *rb,
ram_addr_t start, uint64_t haddr, uint32_t tid)
{
void *aligned = (void *)(uintptr_t)ROUND_DOWN(haddr, qemu_ram_pagesize(rb));
/*
* Discarded pages (via RamDiscardManager) are never migrated. On unlikely
* access, place a zeropage, which will also set the relevant bits in the
* recv_bitmap accordingly, so we won't try placing a zeropage twice.
*
* Checking a single bit is sufficient to handle pagesize > TPS as either
* all relevant bits are set or not.
*/
assert(QEMU_IS_ALIGNED(start, qemu_ram_pagesize(rb)));
if (ramblock_page_is_discarded(rb, start)) {
bool received = ramblock_recv_bitmap_test_byte_offset(rb, start);
return received ? 0 : postcopy_place_page_zero(mis, aligned, rb);
}
return migrate_send_rp_req_pages(mis, rb, start, haddr, tid);
}
/*
* 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)
{
uint64_t aligned_rbo = ROUND_DOWN(rb_offset, qemu_ram_pagesize(rb));
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);
}
/* TODO: support blocktime tracking */
postcopy_request_page(mis, rb, aligned_rbo, client_addr, 0);
return 0;
}
static int blocktime_get_vcpu(PostcopyBlocktimeContext *ctx, uint32_t tid)
{
int *found;
found = g_hash_table_lookup(ctx->tid_to_vcpu_hash, GUINT_TO_POINTER(tid));
if (!found) {
/*
* NOTE: this is possible, because QEMU's non-vCPU threads can
* also access a missing page. Or, when KVM async pf is enabled, a
* fault can even happen from a kworker..
*/
return -1;
}
return *found;
}
static uint64_t get_current_ns(void)
{
return (uint64_t)qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
}
/*
* Inject an (cpu, fault_time) entry into the database, using addr as key.
* When cpu==-1, it means it's a non-vCPU fault.
*/
static void blocktime_fault_inject(PostcopyBlocktimeContext *ctx,
uintptr_t addr, int cpu, uint64_t time)
{
BlocktimeVCPUEntry *entry = blocktime_vcpu_entry_alloc(cpu, time);
GHashTable *table = ctx->vcpu_addr_hash;
gpointer key = (gpointer)addr;
GList *head, *list;
gboolean result;
head = g_hash_table_lookup(table, key);
if (head) {
/*
* If existed, steal the @head for list operation rather than
* freeing it, making sure steal succeeded.
*/
result = g_hash_table_steal(table, key);
assert(result == TRUE);
}
/*
* Now the key is guaranteed to be absent. Two cases:
*
* (1) There's no existing entry, list contains the only one. Insert.
* (2) There're existing entries, after stealing we own it, prepend the
* result and re-insert.
*/
list = g_list_prepend(head, entry);
g_hash_table_insert(table, key, list);
trace_postcopy_blocktime_begin(addr, time, cpu, !!head);
}
/*
* This function is being called when pagefault occurs. It tracks down vCPU
* blocking time. It's protected by @page_request_mutex.
*
* @addr: faulted host virtual address
* @ptid: faulted process thread id
* @rb: ramblock appropriate to addr
*/
void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid,
RAMBlock *rb)
{
int cpu;
MigrationIncomingState *mis = migration_incoming_get_current();
PostcopyBlocktimeContext *dc = mis->blocktime_ctx;
uint64_t current;
if (!dc || ptid == 0) {
return;
}
/*
* The caller should only inject a blocktime entry when the page is
* yet missing.
*/
assert(!ramblock_recv_bitmap_test(rb, (void *)addr));
current = get_current_ns();
cpu = blocktime_get_vcpu(dc, ptid);
if (cpu >= 0) {
/* How many faults on this vCPU in total? */
dc->vcpu_faults_count[cpu]++;
/*
* Account how many concurrent faults on this vCPU we trapped. See
* comments above vcpu_faults_current[] on why it can be more than one.
*/
if (dc->vcpu_faults_current[cpu]++ == 0) {
dc->smp_cpus_down++;
/*
* We use last_begin to cover (1) the 1st fault on this specific
* vCPU, but meanwhile (2) the last vCPU that got blocked. It's
* only used to calculate system-wide blocktime.
*/
dc->last_begin = current;
}
/* Making sure it won't overflow - it really should never! */
assert(dc->vcpu_faults_current[cpu] <= 255);
} else {
/*
* For non-vCPU thread faults, we don't care about tid or cpu index
* or time the thread is blocked (e.g., a kworker trying to help
* KVM when async_pf=on is OK to be blocked and not affect guest
* responsiveness), but we care about latency. Track it with
* cpu=-1.
*
* Note that this will NOT affect blocktime reports on vCPU being
* blocked, but only about system-wide latency reports.
*/
dc->non_vcpu_faults++;
}
blocktime_fault_inject(dc, addr, cpu, current);
}
static void blocktime_latency_account(PostcopyBlocktimeContext *ctx,
uint64_t time_us)
{
/*
* Convert time (in us) to bucket index it belongs. Take extra caution
* of time_us==0 even if normally rare - when happens put into bucket 0.
*/
int index = time_us ? (63 - clz64(time_us)) : 0;
assert(index >= 0);
/* If it's too large, put into top bucket */
if (index >= BLOCKTIME_LATENCY_BUCKET_N) {
index = BLOCKTIME_LATENCY_BUCKET_N - 1;
}
ctx->latency_buckets[index]++;
}
typedef struct {
PostcopyBlocktimeContext *ctx;
uint64_t current;
int affected_cpus;
int affected_non_cpus;
} BlockTimeVCPUIter;
static void blocktime_cpu_list_iter_fn(gpointer data, gpointer user_data)
{
BlockTimeVCPUIter *iter = user_data;
PostcopyBlocktimeContext *ctx = iter->ctx;
BlocktimeVCPUEntry *entry = data;
uint64_t time_passed;
int cpu = entry->cpu;
/*
* Time should never go back.. so when the fault is resolved it must be
* later than when it was faulted.
*/
assert(iter->current >= entry->fault_time);
time_passed = iter->current - entry->fault_time;
/* Latency buckets are in microseconds */
blocktime_latency_account(ctx, time_passed / SCALE_US);
if (cpu >= 0) {
/*
* If we resolved all pending faults on one vCPU due to this page
* resolution, take a note.
*/
if (--ctx->vcpu_faults_current[cpu] == 0) {
ctx->vcpu_blocktime_total[cpu] += time_passed;
iter->affected_cpus += 1;
}
trace_postcopy_blocktime_end_one(cpu, ctx->vcpu_faults_current[cpu]);
} else {
iter->affected_non_cpus++;
ctx->non_vcpu_blocktime_total += time_passed;
/*
* We do not maintain how many pending non-vCPU faults because we
* do not care about blocktime, only latency.
*/
trace_postcopy_blocktime_end_one(-1, 0);
}
}
/*
* This function just provide calculated blocktime per cpu and trace it.
* Total blocktime is calculated in mark_postcopy_blocktime_end. It's
* protected by @page_request_mutex.
*
* 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;
BlockTimeVCPUIter iter = {
.current = get_current_ns(),
.affected_cpus = 0,
.affected_non_cpus = 0,
.ctx = dc,
};
gpointer key = (gpointer)addr;
GHashTable *table;
GList *list;
if (!dc) {
return;
}
table = dc->vcpu_addr_hash;
/* the address wasn't tracked at all? */
list = g_hash_table_lookup(table, key);
if (!list) {
return;
}
/*
* Loop over the set of vCPUs that got blocked on this addr, do the
* blocktime accounting. After that, remove the whole list.
*/
g_list_foreach(list, blocktime_cpu_list_iter_fn, &iter);
g_hash_table_remove(table, key);
/*
* If all vCPUs used to be down, and copying this page would free some
* vCPUs, then the system-level blocktime ends here.
*/
if (dc->smp_cpus_down == smp_cpus && iter.affected_cpus) {
dc->total_blocktime += iter.current - dc->last_begin;
}
dc->smp_cpus_down -= iter.affected_cpus;
trace_postcopy_blocktime_end(addr, iter.current, iter.affected_cpus,
iter.affected_non_cpus);
}
static void 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();
}
/*
* 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_event_set(&mis->thread_sync_event);
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.
*/
postcopy_pause_fault_thread(mis);
}
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 (qatomic_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 = ROUND_DOWN(rb_offset, qemu_ram_pagesize(rb));
trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
qemu_ram_get_idstr(rb),
rb_offset,
msg.arg.pagefault.feat.ptid);
retry:
/*
* Send the request to the source - we want to request one
* of our host page sizes (which is >= TPS)
*/
ret = postcopy_request_page(mis, rb, rb_offset,
msg.arg.pagefault.address,
msg.arg.pagefault.feat.ptid);
if (ret) {
/* May be network failure, try to wait for recovery */
postcopy_pause_fault_thread(mis);
goto retry;
}
}
/* 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;
}
static int postcopy_temp_pages_setup(MigrationIncomingState *mis)
{
PostcopyTmpPage *tmp_page;
int err, i, channels;
void *temp_page;
if (migrate_postcopy_preempt()) {
/* If preemption enabled, need extra channel for urgent requests */
mis->postcopy_channels = RAM_CHANNEL_MAX;
} else {
/* Both precopy/postcopy on the same channel */
mis->postcopy_channels = 1;
}
channels = mis->postcopy_channels;
mis->postcopy_tmp_pages = g_malloc0_n(sizeof(PostcopyTmpPage), channels);
for (i = 0; i < channels; i++) {
tmp_page = &mis->postcopy_tmp_pages[i];
temp_page = mmap(NULL, mis->largest_page_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (temp_page == MAP_FAILED) {
err = errno;
error_report("%s: Failed to map postcopy_tmp_pages[%d]: %s",
__func__, i, strerror(err));
/* Clean up will be done later */
return -err;
}
tmp_page->tmp_huge_page = temp_page;
/* Initialize default states for each tmp page */
postcopy_temp_page_reset(tmp_page);
}
/*
* 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) {
err = errno;
mis->postcopy_tmp_zero_page = NULL;
error_report("%s: Failed to map large zero page %s",
__func__, strerror(err));
return -err;
}
memset(mis->postcopy_tmp_zero_page, '\0', mis->largest_page_size);
return 0;
}
int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
{
Error *local_err = NULL;
/* Open the fd for the kernel to give us userfaults */
mis->userfault_fd = uffd_open(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, &local_err)) {
error_report_err(local_err);
return -1;
}
if (migrate_postcopy_blocktime()) {
assert(mis->blocktime_ctx == NULL);
mis->blocktime_ctx = blocktime_context_new();
}
/* 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;
}
postcopy_thread_create(mis, &mis->fault_thread,
MIGRATION_THREAD_DST_FAULT,
postcopy_ram_fault_thread, QEMU_THREAD_JOINABLE);
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;
}
if (postcopy_temp_pages_setup(mis)) {
/* Error dumped in the sub-function */
return -1;
}
if (migrate_postcopy_preempt()) {
/*
* This thread needs to be created after the temp pages because
* it'll fetch RAM_CHANNEL_POSTCOPY PostcopyTmpPage immediately.
*/
postcopy_thread_create(mis, &mis->postcopy_prio_thread,
MIGRATION_THREAD_DST_PREEMPT,
postcopy_preempt_thread, QEMU_THREAD_JOINABLE);
mis->preempt_thread_status = PREEMPT_THREAD_CREATED;
}
trace_postcopy_ram_enable_notify();
return 0;
}
static int qemu_ufd_copy_ioctl(MigrationIncomingState *mis, void *host_addr,
void *from_addr, uint64_t pagesize, RAMBlock *rb)
{
int userfault_fd = mis->userfault_fd;
int ret;
if (from_addr) {
ret = uffd_copy_page(userfault_fd, host_addr, from_addr, pagesize,
false);
} else {
ret = uffd_zero_page(userfault_fd, host_addr, pagesize, false);
}
if (!ret) {
qemu_mutex_lock(&mis->page_request_mutex);
ramblock_recv_bitmap_set_range(rb, host_addr,
pagesize / qemu_target_page_size());
/*
* If this page resolves a page fault for a previous recorded faulted
* address, take a special note to maintain the requested page list.
*/
if (g_tree_lookup(mis->page_requested, host_addr)) {
g_tree_remove(mis->page_requested, host_addr);
int left_pages = qatomic_dec_fetch(&mis->page_requested_count);
trace_postcopy_page_req_del(host_addr, mis->page_requested_count);
/* Order the update of count and read of preempt status */
smp_mb();
if (mis->preempt_thread_status == PREEMPT_THREAD_QUIT &&
left_pages == 0) {
/*
* This probably means the main thread is waiting for us.
* Notify that we've finished receiving the last requested
* page.
*/
qemu_cond_signal(&mis->page_request_cond);
}
}
mark_postcopy_blocktime_end((uintptr_t)host_addr);
qemu_mutex_unlock(&mis->page_request_mutex);
}
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);
int e;
/* 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.
*/
e = qemu_ufd_copy_ioctl(mis, host, from, pagesize, rb);
if (e) {
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)) {
int e;
e = qemu_ufd_copy_ioctl(mis, host, NULL, pagesize, rb);
if (e) {
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 **errp)
{
error_report("%s: No OS support", __func__);
return false;
}
int postcopy_ram_incoming_init(MigrationIncomingState *mis, Error **errp)
{
error_report("postcopy_ram_incoming_init: No OS support");
return -1;
}
int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
{
g_assert_not_reached();
}
int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
{
g_assert_not_reached();
}
int postcopy_request_shared_page(struct PostCopyFD *pcfd, RAMBlock *rb,
uint64_t client_addr, uint64_t rb_offset)
{
g_assert_not_reached();
}
int postcopy_ram_incoming_setup(MigrationIncomingState *mis)
{
g_assert_not_reached();
}
int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
RAMBlock *rb)
{
g_assert_not_reached();
}
int postcopy_place_page_zero(MigrationIncomingState *mis, void *host,
RAMBlock *rb)
{
g_assert_not_reached();
}
int postcopy_wake_shared(struct PostCopyFD *pcfd,
uint64_t client_addr,
RAMBlock *rb)
{
g_assert_not_reached();
}
void mark_postcopy_blocktime_begin(uintptr_t addr, uint32_t ptid,
RAMBlock *rb)
{
}
#endif
/* ------------------------------------------------------------------------- */
void postcopy_temp_page_reset(PostcopyTmpPage *tmp_page)
{
tmp_page->target_pages = 0;
tmp_page->host_addr = NULL;
/*
* This is set to true when reset, and cleared as long as we received any
* of the non-zero small page within this huge page.
*/
tmp_page->all_zero = true;
}
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 qatomic_load_acquire(&incoming_postcopy_state);
}
/* Set the state and return the old state */
PostcopyState postcopy_state_set(PostcopyState new_state)
{
return qatomic_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;
if (!pcrfds) {
/* migration has already finished and freed the array */
return;
}
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;
}
}
}
void postcopy_preempt_new_channel(MigrationIncomingState *mis, QEMUFile *file)
{
/*
* The new loading channel has its own threads, so it needs to be
* blocked too. It's by default true, just be explicit.
*/
qemu_file_set_blocking(file, true, &error_abort);
mis->postcopy_qemufile_dst = file;
qemu_sem_post(&mis->postcopy_qemufile_dst_done);
trace_postcopy_preempt_new_channel();
}
/*
* Setup the postcopy preempt channel with the IOC. If ERROR is specified,
* setup the error instead. This helper will free the ERROR if specified.
*/
static void
postcopy_preempt_send_channel_done(MigrationState *s,
QIOChannel *ioc, Error *local_err)
{
if (local_err) {
migrate_set_error(s, local_err);
error_free(local_err);
} else {
migration_ioc_register_yank(ioc);
s->postcopy_qemufile_src = qemu_file_new_output(ioc);
trace_postcopy_preempt_new_channel();
}
/*
* Kick the waiter in all cases. The waiter should check upon
* postcopy_qemufile_src to know whether it failed or not.
*/
qemu_sem_post(&s->postcopy_qemufile_src_sem);
}
static void
postcopy_preempt_tls_handshake(QIOTask *task, gpointer opaque)
{
g_autoptr(QIOChannel) ioc = QIO_CHANNEL(qio_task_get_source(task));
MigrationState *s = opaque;
Error *local_err = NULL;
qio_task_propagate_error(task, &local_err);
postcopy_preempt_send_channel_done(s, ioc, local_err);
}
static void
postcopy_preempt_send_channel_new(QIOTask *task, gpointer opaque)
{
g_autoptr(QIOChannel) ioc = QIO_CHANNEL(qio_task_get_source(task));
MigrationState *s = opaque;
QIOChannelTLS *tioc;
Error *local_err = NULL;
if (qio_task_propagate_error(task, &local_err)) {
goto out;
}
if (migrate_channel_requires_tls_upgrade(ioc)) {
tioc = migration_tls_client_create(ioc, s->hostname, &local_err);
if (!tioc) {
goto out;
}
trace_postcopy_preempt_tls_handshake();
qio_channel_set_name(QIO_CHANNEL(tioc), "migration-tls-preempt");
qio_channel_tls_handshake(tioc, postcopy_preempt_tls_handshake,
s, NULL, NULL);
/* Setup the channel until TLS handshake finished */
return;
}
out:
/* This handles both good and error cases */
postcopy_preempt_send_channel_done(s, ioc, local_err);
}
/*
* This function will kick off an async task to establish the preempt
* channel, and wait until the connection setup completed. Returns 0 if
* channel established, -1 for error.
*/
int postcopy_preempt_establish_channel(MigrationState *s)
{
/* If preempt not enabled, no need to wait */
if (!migrate_postcopy_preempt()) {
return 0;
}
/*
* Kick off async task to establish preempt channel. Only do so with
* 8.0+ machines, because 7.1/7.2 require the channel to be created in
* setup phase of migration (even if racy in an unreliable network).
*/
if (!s->preempt_pre_7_2) {
postcopy_preempt_setup(s);
}
/*
* We need the postcopy preempt channel to be established before
* starting doing anything.
*/
qemu_sem_wait(&s->postcopy_qemufile_src_sem);
return s->postcopy_qemufile_src ? 0 : -1;
}
void postcopy_preempt_setup(MigrationState *s)
{
/* Kick an async task to connect */
socket_send_channel_create(postcopy_preempt_send_channel_new, s);
}
static void postcopy_pause_ram_fast_load(MigrationIncomingState *mis)
{
trace_postcopy_pause_fast_load();
qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex);
qemu_sem_wait(&mis->postcopy_pause_sem_fast_load);
qemu_mutex_lock(&mis->postcopy_prio_thread_mutex);
trace_postcopy_pause_fast_load_continued();
}
static bool preempt_thread_should_run(MigrationIncomingState *mis)
{
return mis->preempt_thread_status != PREEMPT_THREAD_QUIT;
}
void *postcopy_preempt_thread(void *opaque)
{
MigrationIncomingState *mis = opaque;
int ret;
trace_postcopy_preempt_thread_entry();
rcu_register_thread();
qemu_event_set(&mis->thread_sync_event);
/*
* The preempt channel is established in asynchronous way. Wait
* for its completion.
*/
qemu_sem_wait(&mis->postcopy_qemufile_dst_done);
/* Sending RAM_SAVE_FLAG_EOS to terminate this thread */
qemu_mutex_lock(&mis->postcopy_prio_thread_mutex);
while (preempt_thread_should_run(mis)) {
ret = ram_load_postcopy(mis->postcopy_qemufile_dst,
RAM_CHANNEL_POSTCOPY);
/* If error happened, go into recovery routine */
if (ret && preempt_thread_should_run(mis)) {
postcopy_pause_ram_fast_load(mis);
} else {
/* We're done */
break;
}
}
qemu_mutex_unlock(&mis->postcopy_prio_thread_mutex);
rcu_unregister_thread();
trace_postcopy_preempt_thread_exit();
return NULL;
}
bool postcopy_is_paused(MigrationStatus status)
{
return status == MIGRATION_STATUS_POSTCOPY_PAUSED ||
status == MIGRATION_STATUS_POSTCOPY_RECOVER_SETUP;
}
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