qemu-kvm/kvm-migration-Implement-switchover-ack-logic.patch

From 387c39f198d94f600be525e363edc7ca916dc261 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@redhat.com>
Date: Wed, 12 Jul 2023 17:46:57 +0200
Subject: [PATCH 11/37] migration: Implement switchover ack logic
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RH-Author: Cédric Le Goater <clg@redhat.com>
RH-MergeRequest: 179: vfio: live migration support
RH-Bugzilla: 2192818
RH-Acked-by: Eric Auger <eric.auger@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Commit: [9/28] 853e1978f3b9f87942863bba894a0ed908bde6b1 (clegoate/qemu-kvm-c9s)

Bugzilla: https://bugzilla.redhat.com/2192818

commit 1b4adb10f898
Author: Avihai Horon <avihaih@nvidia.com>
Date:   Wed Jun 21 14:11:55 2023 +0300

    migration: Implement switchover ack logic

    Implement switchover ack logic. This prevents the source from stopping
    the VM and completing the migration until an ACK is received from the
    destination that it's OK to do so.

    To achieve this, a new SaveVMHandlers handler switchover_ack_needed()
    and a new return path message MIG_RP_MSG_SWITCHOVER_ACK are added.

    The switchover_ack_needed() handler is called during migration setup in
    the destination to check if switchover ack is used by the migrated
    device.

    When switchover is approved by all migrated devices in the destination
    that support this capability, the MIG_RP_MSG_SWITCHOVER_ACK return path
    message is sent to the source to notify it that it's OK to do
    switchover.

    Signed-off-by: Avihai Horon <avihaih@nvidia.com>
    Reviewed-by: Peter Xu <peterx@redhat.com>
    Tested-by: YangHang Liu <yanghliu@redhat.com>
    Acked-by: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: Cédric Le Goater <clg@redhat.com>

Conflicts:
    - migration/migration.c
      context changes due to commit f4584076fc31 ("migration: switch
      from .vm_was_running to .vm_old_state")

Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 include/migration/register.h |  2 ++
 migration/migration.c        | 32 +++++++++++++++++++--
 migration/migration.h        | 14 ++++++++++
 migration/savevm.c           | 54 ++++++++++++++++++++++++++++++++++++
 migration/savevm.h           |  1 +
 migration/trace-events       |  3 ++
 6 files changed, 104 insertions(+), 2 deletions(-)

diff --git a/include/migration/register.h b/include/migration/register.h
index a8dfd8fefd..90914f32f5 100644
--- a/include/migration/register.h
+++ b/include/migration/register.h
@@ -71,6 +71,8 @@ typedef struct SaveVMHandlers {
     int (*load_cleanup)(void *opaque);
     /* Called when postcopy migration wants to resume from failure */
     int (*resume_prepare)(MigrationState *s, void *opaque);
+    /* Checks if switchover ack should be used. Called only in dest */
+    bool (*switchover_ack_needed)(void *opaque);
 } SaveVMHandlers;
 
 int register_savevm_live(const char *idstr,
diff --git a/migration/migration.c b/migration/migration.c
index 1ac5f19bc2..9bf1caee6c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -76,6 +76,7 @@ enum mig_rp_message_type {
     MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
     MIG_RP_MSG_RECV_BITMAP,  /* send recved_bitmap back to source */
     MIG_RP_MSG_RESUME_ACK,   /* tell source that we are ready to resume */
+    MIG_RP_MSG_SWITCHOVER_ACK, /* Tell source it's OK to do switchover */
 
     MIG_RP_MSG_MAX
 };
@@ -756,6 +757,11 @@ bool migration_has_all_channels(void)
     return true;
 }
 
+int migrate_send_rp_switchover_ack(MigrationIncomingState *mis)
+{
+    return migrate_send_rp_message(mis, MIG_RP_MSG_SWITCHOVER_ACK, 0, NULL);
+}
+
 /*
  * Send a 'SHUT' message on the return channel with the given value
  * to indicate that we've finished with the RP.  Non-0 value indicates
@@ -1415,6 +1421,7 @@ void migrate_init(MigrationState *s)
     s->vm_was_running = false;
     s->iteration_initial_bytes = 0;
     s->threshold_size = 0;
+    s->switchover_acked = false;
 }
 
 int migrate_add_blocker_internal(Error *reason, Error **errp)
@@ -1731,6 +1738,7 @@ static struct rp_cmd_args {
     [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
     [MIG_RP_MSG_RECV_BITMAP]    = { .len = -1, .name = "RECV_BITMAP" },
     [MIG_RP_MSG_RESUME_ACK]     = { .len =  4, .name = "RESUME_ACK" },
+    [MIG_RP_MSG_SWITCHOVER_ACK] = { .len =  0, .name = "SWITCHOVER_ACK" },
     [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
 };
 
@@ -1969,6 +1977,11 @@ retry:
             }
             break;
 
+        case MIG_RP_MSG_SWITCHOVER_ACK:
+            ms->switchover_acked = true;
+            trace_source_return_path_thread_switchover_acked();
+            break;
+
         default:
             break;
         }
@@ -2720,6 +2733,20 @@ static void migration_update_counters(MigrationState *s,
                               bandwidth, s->threshold_size);
 }
 
+static bool migration_can_switchover(MigrationState *s)
+{
+    if (!migrate_switchover_ack()) {
+        return true;
+    }
+
+    /* No reason to wait for switchover ACK if VM is stopped */
+    if (!runstate_is_running()) {
+        return true;
+    }
+
+    return s->switchover_acked;
+}
+
 /* Migration thread iteration status */
 typedef enum {
     MIG_ITERATE_RESUME,         /* Resume current iteration */
@@ -2735,6 +2762,7 @@ static MigIterateState migration_iteration_run(MigrationState *s)
 {
     uint64_t must_precopy, can_postcopy;
     bool in_postcopy = s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE;
+    bool can_switchover = migration_can_switchover(s);
 
     qemu_savevm_state_pending_estimate(&must_precopy, &can_postcopy);
     uint64_t pending_size = must_precopy + can_postcopy;
@@ -2747,14 +2775,14 @@ static MigIterateState migration_iteration_run(MigrationState *s)
         trace_migrate_pending_exact(pending_size, must_precopy, can_postcopy);
     }
 
-    if (!pending_size || pending_size < s->threshold_size) {
+    if ((!pending_size || pending_size < s->threshold_size) && can_switchover) {
         trace_migration_thread_low_pending(pending_size);
         migration_completion(s);
         return MIG_ITERATE_BREAK;
     }
 
     /* Still a significant amount to transfer */
-    if (!in_postcopy && must_precopy <= s->threshold_size &&
+    if (!in_postcopy && must_precopy <= s->threshold_size && can_switchover &&
         qatomic_read(&s->start_postcopy)) {
         if (postcopy_start(s)) {
             error_report("%s: postcopy failed to start", __func__);
diff --git a/migration/migration.h b/migration/migration.h
index 2b71df8617..e9679f8029 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -204,6 +204,13 @@ struct MigrationIncomingState {
      * contains valid information.
      */
     QemuMutex page_request_mutex;
+
+    /*
+     * Number of devices that have yet to approve switchover. When this reaches
+     * zero an ACK that it's OK to do switchover is sent to the source. No lock
+     * is needed as this field is updated serially.
+     */
+    unsigned int switchover_ack_pending_num;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
@@ -421,6 +428,12 @@ struct MigrationState {
 
     /* QEMU_VM_VMDESCRIPTION content filled for all non-iterable devices. */
     JSONWriter *vmdesc;
+
+    /*
+     * Indicates whether an ACK from the destination that it's OK to do
+     * switchover has been received.
+     */
+    bool switchover_acked;
 };
 
 void migrate_set_state(int *state, int old_state, int new_state);
@@ -461,6 +474,7 @@ int migrate_send_rp_message_req_pages(MigrationIncomingState *mis,
 void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
                                  char *block_name);
 void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value);
+int migrate_send_rp_switchover_ack(MigrationIncomingState *mis);
 
 void dirty_bitmap_mig_before_vm_start(void);
 void dirty_bitmap_mig_cancel_outgoing(void);
diff --git a/migration/savevm.c b/migration/savevm.c
index 211eff3a8b..aff70e6263 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2358,6 +2358,21 @@ static int loadvm_process_command(QEMUFile *f)
             error_report("CMD_OPEN_RETURN_PATH failed");
             return -1;
         }
+
+        /*
+         * Switchover ack is enabled but no device uses it, so send an ACK to
+         * source that it's OK to switchover. Do it here, after return path has
+         * been created.
+         */
+        if (migrate_switchover_ack() && !mis->switchover_ack_pending_num) {
+            int ret = migrate_send_rp_switchover_ack(mis);
+            if (ret) {
+                error_report(
+                    "Could not send switchover ack RP MSG, err %d (%s)", ret,
+                    strerror(-ret));
+                return ret;
+            }
+        }
         break;
 
     case MIG_CMD_PING:
@@ -2584,6 +2599,23 @@ static int qemu_loadvm_state_header(QEMUFile *f)
     return 0;
 }
 
+static void qemu_loadvm_state_switchover_ack_needed(MigrationIncomingState *mis)
+{
+    SaveStateEntry *se;
+
+    QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
+        if (!se->ops || !se->ops->switchover_ack_needed) {
+            continue;
+        }
+
+        if (se->ops->switchover_ack_needed(se->opaque)) {
+            mis->switchover_ack_pending_num++;
+        }
+    }
+
+    trace_loadvm_state_switchover_ack_needed(mis->switchover_ack_pending_num);
+}
+
 static int qemu_loadvm_state_setup(QEMUFile *f)
 {
     SaveStateEntry *se;
@@ -2787,6 +2819,10 @@ int qemu_loadvm_state(QEMUFile *f)
         return -EINVAL;
     }
 
+    if (migrate_switchover_ack()) {
+        qemu_loadvm_state_switchover_ack_needed(mis);
+    }
+
     cpu_synchronize_all_pre_loadvm();
 
     ret = qemu_loadvm_state_main(f, mis);
@@ -2860,6 +2896,24 @@ int qemu_load_device_state(QEMUFile *f)
     return 0;
 }
 
+int qemu_loadvm_approve_switchover(void)
+{
+    MigrationIncomingState *mis = migration_incoming_get_current();
+
+    if (!mis->switchover_ack_pending_num) {
+        return -EINVAL;
+    }
+
+    mis->switchover_ack_pending_num--;
+    trace_loadvm_approve_switchover(mis->switchover_ack_pending_num);
+
+    if (mis->switchover_ack_pending_num) {
+        return 0;
+    }
+
+    return migrate_send_rp_switchover_ack(mis);
+}
+
 bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
                   bool has_devices, strList *devices, Error **errp)
 {
diff --git a/migration/savevm.h b/migration/savevm.h
index fb636735f0..e894bbc143 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -65,6 +65,7 @@ int qemu_loadvm_state(QEMUFile *f);
 void qemu_loadvm_state_cleanup(void);
 int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis);
 int qemu_load_device_state(QEMUFile *f);
+int qemu_loadvm_approve_switchover(void);
 int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
         bool in_postcopy, bool inactivate_disks);
 
diff --git a/migration/trace-events b/migration/trace-events
index 92161eeac5..cda807d271 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -7,6 +7,7 @@ qemu_loadvm_state_section_partend(uint32_t section_id) "%u"
 qemu_loadvm_state_post_main(int ret) "%d"
 qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u"
 qemu_savevm_send_packaged(void) ""
+loadvm_state_switchover_ack_needed(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u"
 loadvm_state_setup(void) ""
 loadvm_state_cleanup(void) ""
 loadvm_handle_cmd_packaged(unsigned int length) "%u"
@@ -23,6 +24,7 @@ loadvm_postcopy_ram_handle_discard_end(void) ""
 loadvm_postcopy_ram_handle_discard_header(const char *ramid, uint16_t len) "%s: %ud"
 loadvm_process_command(const char *s, uint16_t len) "com=%s len=%d"
 loadvm_process_command_ping(uint32_t val) "0x%x"
+loadvm_approve_switchover(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u"
 postcopy_ram_listen_thread_exit(void) ""
 postcopy_ram_listen_thread_start(void) ""
 qemu_savevm_send_postcopy_advise(void) ""
@@ -180,6 +182,7 @@ source_return_path_thread_loop_top(void) ""
 source_return_path_thread_pong(uint32_t val) "0x%x"
 source_return_path_thread_shut(uint32_t val) "0x%x"
 source_return_path_thread_resume_ack(uint32_t v) "%"PRIu32
+source_return_path_thread_switchover_acked(void) ""
 migration_thread_low_pending(uint64_t pending) "%" PRIu64
 migrate_transferred(uint64_t tranferred, uint64_t time_spent, uint64_t bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " bandwidth %" PRIu64 " max_size %" PRId64
 process_incoming_migration_co_end(int ret, int ps) "ret=%d postcopy-state=%d"
-- 
2.39.3