Merge remote-tracking branch 'remotes/amit-migration/tags/migration-for-2.8' into staging

Migration bits from the COLO project

# gpg: Signature made Sun 30 Oct 2016 10:39:55 GMT
# gpg:                using RSA key 0xEB0B4DFC657EF670
# gpg: Good signature from "Amit Shah <amit@amitshah.net>"
# gpg:                 aka "Amit Shah <amit@kernel.org>"
# gpg:                 aka "Amit Shah <amitshah@gmx.net>"
# Primary key fingerprint: 48CA 3722 5FE7 F4A8 B337  2735 1E9A 3B5F 8540 83B6
#      Subkey fingerprint: CC63 D332 AB8F 4617 4529  6534 EB0B 4DFC 657E F670

* remotes/amit-migration/tags/migration-for-2.8:
  MAINTAINERS: Add maintainer for COLO framework related files
  configure: Support enable/disable COLO feature
  docs: Add documentation for COLO feature
  COLO: Implement failover work for secondary VM
  COLO: Implement the process of failover for primary VM
  COLO: Introduce state to record failover process
  COLO: Add 'x-colo-lost-heartbeat' command to trigger failover
  COLO: Synchronize PVM's state to SVM periodically
  COLO: Add checkpoint-delay parameter for migrate-set-parameters
  COLO: Load VMState into QIOChannelBuffer before restore it
  COLO: Send PVM state to secondary side when do checkpoint
  COLO: Add a new RunState RUN_STATE_COLO
  COLO: Introduce checkpointing protocol
  COLO: Establish a new communicating path for COLO
  migration: Switch to COLO process after finishing loadvm
  migration: Enter into COLO mode after migration if COLO is enabled
  COLO: migrate COLO related info to secondary node
  migration: Introduce capability 'x-colo' to migration

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

7 files changed, 798 insertions, 15 deletions

diff --git a/migration/Makefile.objs b/migration/Makefile.objs
index 30ad945..3f3e237 100644
--- a/migration/Makefile.objs
+++ b/migration/Makefile.objs
@@ -1,5 +1,7 @@
 common-obj-y += migration.o socket.o fd.o exec.o
 common-obj-y += tls.o
+common-obj-y += colo-comm.o
+common-obj-$(CONFIG_COLO) += colo.o colo-failover.o
 common-obj-y += vmstate.o
 common-obj-y += qemu-file.o
 common-obj-y += qemu-file-channel.o
diff --git a/migration/colo-comm.c b/migration/colo-comm.c
new file mode 100644
index 0000000..20b60ec
--- /dev/null
+++ b/migration/colo-comm.c
@@ -0,0 +1,72 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later. See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include <migration/colo.h>
+#include "trace.h"
+
+typedef struct {
+     bool colo_requested;
+} COLOInfo;
+
+static COLOInfo colo_info;
+
+COLOMode get_colo_mode(void)
+{
+    if (migration_in_colo_state()) {
+        return COLO_MODE_PRIMARY;
+    } else if (migration_incoming_in_colo_state()) {
+        return COLO_MODE_SECONDARY;
+    } else {
+        return COLO_MODE_UNKNOWN;
+    }
+}
+
+static void colo_info_pre_save(void *opaque)
+{
+    COLOInfo *s = opaque;
+
+    s->colo_requested = migrate_colo_enabled();
+}
+
+static bool colo_info_need(void *opaque)
+{
+   return migrate_colo_enabled();
+}
+
+static const VMStateDescription colo_state = {
+    .name = "COLOState",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .pre_save = colo_info_pre_save,
+    .needed = colo_info_need,
+    .fields = (VMStateField[]) {
+        VMSTATE_BOOL(colo_requested, COLOInfo),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
+void colo_info_init(void)
+{
+    vmstate_register(NULL, 0, &colo_state, &colo_info);
+}
+
+bool migration_incoming_enable_colo(void)
+{
+    return colo_info.colo_requested;
+}
+
+void migration_incoming_exit_colo(void)
+{
+    colo_info.colo_requested = false;
+}
diff --git a/migration/colo-failover.c b/migration/colo-failover.c
new file mode 100644
index 0000000..cc229f5
--- /dev/null
+++ b/migration/colo-failover.c
@@ -0,0 +1,83 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "migration/colo.h"
+#include "migration/failover.h"
+#include "qmp-commands.h"
+#include "qapi/qmp/qerror.h"
+#include "qemu/error-report.h"
+#include "trace.h"
+
+static QEMUBH *failover_bh;
+static FailoverStatus failover_state;
+
+static void colo_failover_bh(void *opaque)
+{
+    int old_state;
+
+    qemu_bh_delete(failover_bh);
+    failover_bh = NULL;
+
+    old_state = failover_set_state(FAILOVER_STATUS_REQUIRE,
+                                   FAILOVER_STATUS_ACTIVE);
+    if (old_state != FAILOVER_STATUS_REQUIRE) {
+        error_report("Unknown error for failover, old_state = %s",
+                    FailoverStatus_lookup[old_state]);
+        return;
+    }
+
+    colo_do_failover(NULL);
+}
+
+void failover_request_active(Error **errp)
+{
+   if (failover_set_state(FAILOVER_STATUS_NONE,
+        FAILOVER_STATUS_REQUIRE) != FAILOVER_STATUS_NONE) {
+        error_setg(errp, "COLO failover is already actived");
+        return;
+    }
+    failover_bh = qemu_bh_new(colo_failover_bh, NULL);
+    qemu_bh_schedule(failover_bh);
+}
+
+void failover_init_state(void)
+{
+    failover_state = FAILOVER_STATUS_NONE;
+}
+
+FailoverStatus failover_set_state(FailoverStatus old_state,
+                    FailoverStatus new_state)
+{
+    FailoverStatus old;
+
+    old = atomic_cmpxchg(&failover_state, old_state, new_state);
+    if (old == old_state) {
+        trace_colo_failover_set_state(FailoverStatus_lookup[new_state]);
+    }
+    return old;
+}
+
+FailoverStatus failover_get_state(void)
+{
+    return atomic_read(&failover_state);
+}
+
+void qmp_x_colo_lost_heartbeat(Error **errp)
+{
+    if (get_colo_mode() == COLO_MODE_UNKNOWN) {
+        error_setg(errp, QERR_FEATURE_DISABLED, "colo");
+        return;
+    }
+
+    failover_request_active(errp);
+}
diff --git a/migration/colo.c b/migration/colo.c
new file mode 100644
index 0000000..e7224b8
--- /dev/null
+++ b/migration/colo.c
@@ -0,0 +1,529 @@
+/*
+ * COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
+ * (a.k.a. Fault Tolerance or Continuous Replication)
+ *
+ * Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
+ * Copyright (c) 2016 FUJITSU LIMITED
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/timer.h"
+#include "sysemu/sysemu.h"
+#include "migration/colo.h"
+#include "io/channel-buffer.h"
+#include "trace.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+#include "migration/failover.h"
+
+#define COLO_BUFFER_BASE_SIZE (4 * 1024 * 1024)
+
+bool colo_supported(void)
+{
+    return true;
+}
+
+bool migration_in_colo_state(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return (s->state == MIGRATION_STATUS_COLO);
+}
+
+bool migration_incoming_in_colo_state(void)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    return mis && (mis->state == MIGRATION_STATUS_COLO);
+}
+
+static bool colo_runstate_is_stopped(void)
+{
+    return runstate_check(RUN_STATE_COLO) || !runstate_is_running();
+}
+
+static void secondary_vm_do_failover(void)
+{
+    int old_state;
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    migrate_set_state(&mis->state, MIGRATION_STATUS_COLO,
+                      MIGRATION_STATUS_COMPLETED);
+
+    if (!autostart) {
+        error_report("\"-S\" qemu option will be ignored in secondary side");
+        /* recover runstate to normal migration finish state */
+        autostart = true;
+    }
+
+    old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
+                                   FAILOVER_STATUS_COMPLETED);
+    if (old_state != FAILOVER_STATUS_ACTIVE) {
+        error_report("Incorrect state (%s) while doing failover for "
+                     "secondary VM", FailoverStatus_lookup[old_state]);
+        return;
+    }
+    /* For Secondary VM, jump to incoming co */
+    if (mis->migration_incoming_co) {
+        qemu_coroutine_enter(mis->migration_incoming_co);
+    }
+}
+
+static void primary_vm_do_failover(void)
+{
+    MigrationState *s = migrate_get_current();
+    int old_state;
+
+    migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
+                      MIGRATION_STATUS_COMPLETED);
+
+    old_state = failover_set_state(FAILOVER_STATUS_ACTIVE,
+                                   FAILOVER_STATUS_COMPLETED);
+    if (old_state != FAILOVER_STATUS_ACTIVE) {
+        error_report("Incorrect state (%s) while doing failover for Primary VM",
+                     FailoverStatus_lookup[old_state]);
+        return;
+    }
+}
+
+void colo_do_failover(MigrationState *s)
+{
+    /* Make sure VM stopped while failover happened. */
+    if (!colo_runstate_is_stopped()) {
+        vm_stop_force_state(RUN_STATE_COLO);
+    }
+
+    if (get_colo_mode() == COLO_MODE_PRIMARY) {
+        primary_vm_do_failover();
+    } else {
+        secondary_vm_do_failover();
+    }
+}
+
+static void colo_send_message(QEMUFile *f, COLOMessage msg,
+                              Error **errp)
+{
+    int ret;
+
+    if (msg >= COLO_MESSAGE__MAX) {
+        error_setg(errp, "%s: Invalid message", __func__);
+        return;
+    }
+    qemu_put_be32(f, msg);
+    qemu_fflush(f);
+
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Can't send COLO message");
+    }
+    trace_colo_send_message(COLOMessage_lookup[msg]);
+}
+
+static void colo_send_message_value(QEMUFile *f, COLOMessage msg,
+                                    uint64_t value, Error **errp)
+{
+    Error *local_err = NULL;
+    int ret;
+
+    colo_send_message(f, msg, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+    qemu_put_be64(f, value);
+    qemu_fflush(f);
+
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed to send value for message:%s",
+                         COLOMessage_lookup[msg]);
+    }
+}
+
+static COLOMessage colo_receive_message(QEMUFile *f, Error **errp)
+{
+    COLOMessage msg;
+    int ret;
+
+    msg = qemu_get_be32(f);
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Can't receive COLO message");
+        return msg;
+    }
+    if (msg >= COLO_MESSAGE__MAX) {
+        error_setg(errp, "%s: Invalid message", __func__);
+        return msg;
+    }
+    trace_colo_receive_message(COLOMessage_lookup[msg]);
+    return msg;
+}
+
+static void colo_receive_check_message(QEMUFile *f, COLOMessage expect_msg,
+                                       Error **errp)
+{
+    COLOMessage msg;
+    Error *local_err = NULL;
+
+    msg = colo_receive_message(f, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+    if (msg != expect_msg) {
+        error_setg(errp, "Unexpected COLO message %d, expected %d",
+                          msg, expect_msg);
+    }
+}
+
+static uint64_t colo_receive_message_value(QEMUFile *f, uint32_t expect_msg,
+                                           Error **errp)
+{
+    Error *local_err = NULL;
+    uint64_t value;
+    int ret;
+
+    colo_receive_check_message(f, expect_msg, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return 0;
+    }
+
+    value = qemu_get_be64(f);
+    ret = qemu_file_get_error(f);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed to get value for COLO message: %s",
+                         COLOMessage_lookup[expect_msg]);
+    }
+    return value;
+}
+
+static int colo_do_checkpoint_transaction(MigrationState *s,
+                                          QIOChannelBuffer *bioc,
+                                          QEMUFile *fb)
+{
+    Error *local_err = NULL;
+    int ret = -1;
+
+    colo_send_message(s->to_dst_file, COLO_MESSAGE_CHECKPOINT_REQUEST,
+                      &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    colo_receive_check_message(s->rp_state.from_dst_file,
+                    COLO_MESSAGE_CHECKPOINT_REPLY, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    /* Reset channel-buffer directly */
+    qio_channel_io_seek(QIO_CHANNEL(bioc), 0, 0, NULL);
+    bioc->usage = 0;
+
+    qemu_mutex_lock_iothread();
+    if (failover_get_state() != FAILOVER_STATUS_NONE) {
+        qemu_mutex_unlock_iothread();
+        goto out;
+    }
+    vm_stop_force_state(RUN_STATE_COLO);
+    qemu_mutex_unlock_iothread();
+    trace_colo_vm_state_change("run", "stop");
+    /*
+     * Failover request bh could be called after vm_stop_force_state(),
+     * So we need check failover_request_is_active() again.
+     */
+    if (failover_get_state() != FAILOVER_STATUS_NONE) {
+        goto out;
+    }
+
+    /* Disable block migration */
+    s->params.blk = 0;
+    s->params.shared = 0;
+    qemu_savevm_state_header(fb);
+    qemu_savevm_state_begin(fb, &s->params);
+    qemu_mutex_lock_iothread();
+    qemu_savevm_state_complete_precopy(fb, false);
+    qemu_mutex_unlock_iothread();
+
+    qemu_fflush(fb);
+
+    colo_send_message(s->to_dst_file, COLO_MESSAGE_VMSTATE_SEND, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    /*
+     * We need the size of the VMstate data in Secondary side,
+     * With which we can decide how much data should be read.
+     */
+    colo_send_message_value(s->to_dst_file, COLO_MESSAGE_VMSTATE_SIZE,
+                            bioc->usage, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    qemu_put_buffer(s->to_dst_file, bioc->data, bioc->usage);
+    qemu_fflush(s->to_dst_file);
+    ret = qemu_file_get_error(s->to_dst_file);
+    if (ret < 0) {
+        goto out;
+    }
+
+    colo_receive_check_message(s->rp_state.from_dst_file,
+                       COLO_MESSAGE_VMSTATE_RECEIVED, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    colo_receive_check_message(s->rp_state.from_dst_file,
+                       COLO_MESSAGE_VMSTATE_LOADED, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    ret = 0;
+
+    qemu_mutex_lock_iothread();
+    vm_start();
+    qemu_mutex_unlock_iothread();
+    trace_colo_vm_state_change("stop", "run");
+
+out:
+    if (local_err) {
+        error_report_err(local_err);
+    }
+    return ret;
+}
+
+static void colo_process_checkpoint(MigrationState *s)
+{
+    QIOChannelBuffer *bioc;
+    QEMUFile *fb = NULL;
+    int64_t current_time, checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+    Error *local_err = NULL;
+    int ret;
+
+    failover_init_state();
+
+    s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
+    if (!s->rp_state.from_dst_file) {
+        error_report("Open QEMUFile from_dst_file failed");
+        goto out;
+    }
+
+    /*
+     * Wait for Secondary finish loading VM states and enter COLO
+     * restore.
+     */
+    colo_receive_check_message(s->rp_state.from_dst_file,
+                       COLO_MESSAGE_CHECKPOINT_READY, &local_err);
+    if (local_err) {
+        goto out;
+    }
+    bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE);
+    fb = qemu_fopen_channel_output(QIO_CHANNEL(bioc));
+    object_unref(OBJECT(bioc));
+
+    qemu_mutex_lock_iothread();
+    vm_start();
+    qemu_mutex_unlock_iothread();
+    trace_colo_vm_state_change("stop", "run");
+
+    while (s->state == MIGRATION_STATUS_COLO) {
+        if (failover_get_state() != FAILOVER_STATUS_NONE) {
+            error_report("failover request");
+            goto out;
+        }
+
+        current_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+        if (current_time - checkpoint_time <
+            s->parameters.x_checkpoint_delay) {
+            int64_t delay_ms;
+
+            delay_ms = s->parameters.x_checkpoint_delay -
+                       (current_time - checkpoint_time);
+            g_usleep(delay_ms * 1000);
+        }
+        ret = colo_do_checkpoint_transaction(s, bioc, fb);
+        if (ret < 0) {
+            goto out;
+        }
+        checkpoint_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
+    }
+
+out:
+    /* Throw the unreported error message after exited from loop */
+    if (local_err) {
+        error_report_err(local_err);
+    }
+
+    if (fb) {
+        qemu_fclose(fb);
+    }
+
+    if (s->rp_state.from_dst_file) {
+        qemu_fclose(s->rp_state.from_dst_file);
+    }
+}
+
+void migrate_start_colo_process(MigrationState *s)
+{
+    qemu_mutex_unlock_iothread();
+    migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
+                      MIGRATION_STATUS_COLO);
+    colo_process_checkpoint(s);
+    qemu_mutex_lock_iothread();
+}
+
+static void colo_wait_handle_message(QEMUFile *f, int *checkpoint_request,
+                                     Error **errp)
+{
+    COLOMessage msg;
+    Error *local_err = NULL;
+
+    msg = colo_receive_message(f, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    switch (msg) {
+    case COLO_MESSAGE_CHECKPOINT_REQUEST:
+        *checkpoint_request = 1;
+        break;
+    default:
+        *checkpoint_request = 0;
+        error_setg(errp, "Got unknown COLO message: %d", msg);
+        break;
+    }
+}
+
+void *colo_process_incoming_thread(void *opaque)
+{
+    MigrationIncomingState *mis = opaque;
+    QEMUFile *fb = NULL;
+    QIOChannelBuffer *bioc = NULL; /* Cache incoming device state */
+    uint64_t total_size;
+    uint64_t value;
+    Error *local_err = NULL;
+
+    migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
+                      MIGRATION_STATUS_COLO);
+
+    failover_init_state();
+
+    mis->to_src_file = qemu_file_get_return_path(mis->from_src_file);
+    if (!mis->to_src_file) {
+        error_report("COLO incoming thread: Open QEMUFile to_src_file failed");
+        goto out;
+    }
+    /*
+     * Note: the communication between Primary side and Secondary side
+     * should be sequential, we set the fd to unblocked in migration incoming
+     * coroutine, and here we are in the COLO incoming thread, so it is ok to
+     * set the fd back to blocked.
+     */
+    qemu_file_set_blocking(mis->from_src_file, true);
+
+    bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE);
+    fb = qemu_fopen_channel_input(QIO_CHANNEL(bioc));
+    object_unref(OBJECT(bioc));
+
+    colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_READY,
+                      &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    while (mis->state == MIGRATION_STATUS_COLO) {
+        int request;
+
+        colo_wait_handle_message(mis->from_src_file, &request, &local_err);
+        if (local_err) {
+            goto out;
+        }
+        assert(request);
+        if (failover_get_state() != FAILOVER_STATUS_NONE) {
+            error_report("failover request");
+            goto out;
+        }
+
+        /* FIXME: This is unnecessary for periodic checkpoint mode */
+        colo_send_message(mis->to_src_file, COLO_MESSAGE_CHECKPOINT_REPLY,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        colo_receive_check_message(mis->from_src_file,
+                           COLO_MESSAGE_VMSTATE_SEND, &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        value = colo_receive_message_value(mis->from_src_file,
+                                 COLO_MESSAGE_VMSTATE_SIZE, &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        /*
+         * Read VM device state data into channel buffer,
+         * It's better to re-use the memory allocated.
+         * Here we need to handle the channel buffer directly.
+         */
+        if (value > bioc->capacity) {
+            bioc->capacity = value;
+            bioc->data = g_realloc(bioc->data, bioc->capacity);
+        }
+        total_size = qemu_get_buffer(mis->from_src_file, bioc->data, value);
+        if (total_size != value) {
+            error_report("Got %" PRIu64 " VMState data, less than expected"
+                        " %" PRIu64, total_size, value);
+            goto out;
+        }
+        bioc->usage = total_size;
+        qio_channel_io_seek(QIO_CHANNEL(bioc), 0, 0, NULL);
+
+        colo_send_message(mis->to_src_file, COLO_MESSAGE_VMSTATE_RECEIVED,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+
+        qemu_mutex_lock_iothread();
+        qemu_system_reset(VMRESET_SILENT);
+        if (qemu_loadvm_state(fb) < 0) {
+            error_report("COLO: loadvm failed");
+            qemu_mutex_unlock_iothread();
+            goto out;
+        }
+        qemu_mutex_unlock_iothread();
+
+        colo_send_message(mis->to_src_file, COLO_MESSAGE_VMSTATE_LOADED,
+                     &local_err);
+        if (local_err) {
+            goto out;
+        }
+    }
+
+out:
+    /* Throw the unreported error message after exited from loop */
+    if (local_err) {
+        error_report_err(local_err);
+    }
+
+    if (fb) {
+        qemu_fclose(fb);
+    }
+
+    if (mis->to_src_file) {
+        qemu_fclose(mis->to_src_file);
+    }
+    migration_incoming_exit_colo();
+
+    return NULL;
+}
diff --git a/migration/migration.c b/migration/migration.c
index 4084eb6..e331f28 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -36,6 +36,7 @@
 #include "exec/address-spaces.h"
 #include "io/channel-buffer.h"
 #include "io/channel-tls.h"
+#include "migration/colo.h"
 
 #define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */
 
@@ -62,6 +63,11 @@
 /* Migration XBZRLE default cache size */
 #define DEFAULT_MIGRATE_CACHE_SIZE (64 * 1024 * 1024)
 
+/* The delay time (in ms) between two COLO checkpoints
+ * Note: Please change this default value to 10000 when we support hybrid mode.
+ */
+#define DEFAULT_MIGRATE_X_CHECKPOINT_DELAY 200
+
 static NotifierList migration_state_notifiers =
     NOTIFIER_LIST_INITIALIZER(migration_state_notifiers);
 
@@ -94,6 +100,7 @@ MigrationState *migrate_get_current(void)
             .cpu_throttle_increment = DEFAULT_MIGRATE_CPU_THROTTLE_INCREMENT,
             .max_bandwidth = MAX_THROTTLE,
             .downtime_limit = DEFAULT_MIGRATE_SET_DOWNTIME,
+            .x_checkpoint_delay = DEFAULT_MIGRATE_X_CHECKPOINT_DELAY,
         },
     };
 
@@ -406,6 +413,18 @@ static void process_incoming_migration_co(void *opaque)
         /* Else if something went wrong then just fall out of the normal exit */
     }
 
+    /* we get COLO info, and know if we are in COLO mode */
+    if (!ret && migration_incoming_enable_colo()) {
+        mis->migration_incoming_co = qemu_coroutine_self();
+        qemu_thread_create(&mis->colo_incoming_thread, "COLO incoming",
+             colo_process_incoming_thread, mis, QEMU_THREAD_JOINABLE);
+        mis->have_colo_incoming_thread = true;
+        qemu_coroutine_yield();
+
+        /* Wait checkpoint incoming thread exit before free resource */
+        qemu_thread_join(&mis->colo_incoming_thread);
+    }
+
     qemu_fclose(f);
     free_xbzrle_decoded_buf();
 
@@ -531,6 +550,9 @@ MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
 
     caps = NULL; /* silence compiler warning */
     for (i = 0; i < MIGRATION_CAPABILITY__MAX; i++) {
+        if (i == MIGRATION_CAPABILITY_X_COLO && !colo_supported()) {
+            continue;
+        }
         if (head == NULL) {
             head = g_malloc0(sizeof(*caps));
             caps = head;
@@ -571,6 +593,7 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->max_bandwidth = s->parameters.max_bandwidth;
     params->has_downtime_limit = true;
     params->downtime_limit = s->parameters.downtime_limit;
+    params->x_checkpoint_delay = s->parameters.x_checkpoint_delay;
 
     return params;
 }
@@ -691,6 +714,10 @@ MigrationInfo *qmp_query_migrate(Error **errp)
 
         get_xbzrle_cache_stats(info);
         break;
+    case MIGRATION_STATUS_COLO:
+        info->has_status = true;
+        /* TODO: display COLO specific information (checkpoint info etc.) */
+        break;
     case MIGRATION_STATUS_COMPLETED:
         get_xbzrle_cache_stats(info);
 
@@ -733,6 +760,14 @@ void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
     }
 
     for (cap = params; cap; cap = cap->next) {
+        if (cap->value->capability == MIGRATION_CAPABILITY_X_COLO) {
+            if (!colo_supported()) {
+                error_setg(errp, "COLO is not currently supported, please"
+                             " configure with --enable-colo option in order to"
+                             " support COLO feature");
+                continue;
+            }
+        }
         s->enabled_capabilities[cap->value->capability] = cap->value->state;
     }
 
@@ -817,6 +852,11 @@ void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
                    "an integer in the range of 0 to 2000000 milliseconds");
         return;
     }
+    if (params->has_x_checkpoint_delay && (params->x_checkpoint_delay < 0)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                    "x_checkpoint_delay",
+                    "is invalid, it should be positive");
+    }
 
     if (params->has_compress_level) {
         s->parameters.compress_level = params->compress_level;
@@ -851,6 +891,10 @@ void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
     if (params->has_downtime_limit) {
         s->parameters.downtime_limit = params->downtime_limit;
     }
+
+    if (params->has_x_checkpoint_delay) {
+        s->parameters.x_checkpoint_delay = params->x_checkpoint_delay;
+    }
 }
 
 
@@ -1101,7 +1145,8 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
     params.shared = has_inc && inc;
 
     if (migration_is_setup_or_active(s->state) ||
-        s->state == MIGRATION_STATUS_CANCELLING) {
+        s->state == MIGRATION_STATUS_CANCELLING ||
+        s->state == MIGRATION_STATUS_COLO) {
         error_setg(errp, QERR_MIGRATION_ACTIVE);
         return;
     }
@@ -1649,7 +1694,11 @@ static void migration_completion(MigrationState *s, int current_active_state,
 
         if (!ret) {
             ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
-            if (ret >= 0) {
+            /*
+             * Don't mark the image with BDRV_O_INACTIVE flag if
+             * we will go into COLO stage later.
+             */
+            if (ret >= 0 && !migrate_colo_enabled()) {
                 ret = bdrv_inactivate_all();
             }
             if (ret >= 0) {
@@ -1691,8 +1740,11 @@ static void migration_completion(MigrationState *s, int current_active_state,
         goto fail_invalidate;
     }
 
-    migrate_set_state(&s->state, current_active_state,
-                      MIGRATION_STATUS_COMPLETED);
+    if (!migrate_colo_enabled()) {
+        migrate_set_state(&s->state, current_active_state,
+                          MIGRATION_STATUS_COMPLETED);
+    }
+
     return;
 
 fail_invalidate:
@@ -1713,6 +1765,12 @@ fail:
                       MIGRATION_STATUS_FAILED);
 }
 
+bool migrate_colo_enabled(void)
+{
+    MigrationState *s = migrate_get_current();
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_X_COLO];
+}
+
 /*
  * Master migration thread on the source VM.
  * It drives the migration and pumps the data down the outgoing channel.
@@ -1731,6 +1789,7 @@ static void *migration_thread(void *opaque)
     bool entered_postcopy = false;
     /* The active state we expect to be in; ACTIVE or POSTCOPY_ACTIVE */
     enum MigrationStatus current_active_state = MIGRATION_STATUS_ACTIVE;
+    bool enable_colo = migrate_colo_enabled();
 
     rcu_register_thread();
 
@@ -1839,7 +1898,13 @@ static void *migration_thread(void *opaque)
     end_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
 
     qemu_mutex_lock_iothread();
-    qemu_savevm_state_cleanup();
+    /*
+     * The resource has been allocated by migration will be reused in COLO
+     * process, so don't release them.
+     */
+    if (!enable_colo) {
+        qemu_savevm_state_cleanup();
+    }
     if (s->state == MIGRATION_STATUS_COMPLETED) {
         uint64_t transferred_bytes = qemu_ftell(s->to_dst_file);
         s->total_time = end_time - s->total_time;
@@ -1852,6 +1917,15 @@ static void *migration_thread(void *opaque)
         }
         runstate_set(RUN_STATE_POSTMIGRATE);
     } else {
+        if (s->state == MIGRATION_STATUS_ACTIVE && enable_colo) {
+            migrate_start_colo_process(s);
+            qemu_savevm_state_cleanup();
+            /*
+            * Fixme: we will run VM in COLO no matter its old running state.
+            * After exited COLO, we will keep running.
+            */
+            old_vm_running = true;
+        }
         if (old_vm_running && !entered_postcopy) {
             vm_start();
         } else {
diff --git a/migration/ram.c b/migration/ram.c
index d032d38..fb9252d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -43,6 +43,7 @@
 #include "trace.h"
 #include "exec/ram_addr.h"
 #include "qemu/rcu_queue.h"
+#include "migration/colo.h"
 
 #ifdef DEBUG_MIGRATION_RAM
 #define DPRINTF(fmt, ...) \
@@ -1871,16 +1872,8 @@ err:
     return ret;
 }
 
-
-/* Each of ram_save_setup, ram_save_iterate and ram_save_complete has
- * long-running RCU critical section.  When rcu-reclaims in the code
- * start to become numerous it will be necessary to reduce the
- * granularity of these critical sections.
- */
-
-static int ram_save_setup(QEMUFile *f, void *opaque)
+static int ram_save_init_globals(void)
 {
-    RAMBlock *block;
     int64_t ram_bitmap_pages; /* Size of bitmap in pages, including gaps */
 
     dirty_rate_high_cnt = 0;
@@ -1947,6 +1940,29 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     migration_bitmap_sync();
     qemu_mutex_unlock_ramlist();
     qemu_mutex_unlock_iothread();
+    rcu_read_unlock();
+
+    return 0;
+}
+
+/* Each of ram_save_setup, ram_save_iterate and ram_save_complete has
+ * long-running RCU critical section.  When rcu-reclaims in the code
+ * start to become numerous it will be necessary to reduce the
+ * granularity of these critical sections.
+ */
+
+static int ram_save_setup(QEMUFile *f, void *opaque)
+{
+    RAMBlock *block;
+
+    /* migration has already setup the bitmap, reuse it. */
+    if (!migration_in_colo_state()) {
+        if (ram_save_init_globals() < 0) {
+            return -1;
+         }
+    }
+
+    rcu_read_lock();
 
     qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE);
 
@@ -2048,7 +2064,8 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
     while (true) {
         int pages;
 
-        pages = ram_find_and_save_block(f, true, &bytes_transferred);
+        pages = ram_find_and_save_block(f, !migration_in_colo_state(),
+                                        &bytes_transferred);
         /* no more blocks to sent */
         if (pages == 0) {
             break;
diff --git a/migration/trace-events b/migration/trace-events
index dfee75a..94134f7 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -207,3 +207,9 @@ migration_tls_outgoing_handshake_complete(void) ""
 migration_tls_incoming_handshake_start(void) ""
 migration_tls_incoming_handshake_error(const char *err) "err=%s"
 migration_tls_incoming_handshake_complete(void) ""
+
+# migration/colo.c
+colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
+colo_send_message(const char *msg) "Send '%s' message"
+colo_receive_message(const char *msg) "Receive '%s' message"
+colo_failover_set_state(const char *new_state) "new state %s"