Re: [PATCH V3 10/13] migration: stop vm for cpr

[Steven Sistare]

On 2/20/2024 2:33 AM, Peter Xu wrote:
> On Thu, Feb 08, 2024 at 10:54:03AM -0800, Steve Sistare wrote:
>> When migration for cpr is initiated, stop the vm and set state
>> RUN_STATE_FINISH_MIGRATE before ram is saved.  This eliminates the
>> possibility of ram and device state being out of sync, and guarantees
>> that a guest in the suspended state remains suspended, because qmp_cont
>> rejects a cont command in the RUN_STATE_FINISH_MIGRATE state.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  include/migration/misc.h |  1 +
>>  migration/migration.c    | 32 +++++++++++++++++++++++++-------
>>  2 files changed, 26 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/migration/misc.h b/include/migration/misc.h
>> index 6dc234b..54c99a3 100644
>> --- a/include/migration/misc.h
>> +++ b/include/migration/misc.h
>> @@ -60,6 +60,7 @@ void migration_object_init(void);
>>  void migration_shutdown(void);
>>  bool migration_is_idle(void);
>>  bool migration_is_active(MigrationState *);
>> +bool migrate_mode_is_cpr(MigrationState *);
>>  
>>  typedef enum MigrationEventType {
>>      MIG_EVENT_PRECOPY_SETUP,
>> diff --git a/migration/migration.c b/migration/migration.c
>> index d1fce9e..fc5c587 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -1603,6 +1603,11 @@ bool migration_is_active(MigrationState *s)
>>              s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
>>  }
>>  
>> +bool migrate_mode_is_cpr(MigrationState *s)
>> +{
>> +    return s->parameters.mode == MIG_MODE_CPR_REBOOT;
>> +}
>> +
>>  int migrate_init(MigrationState *s, Error **errp)
>>  {
>>      int ret;
>> @@ -2651,13 +2656,14 @@ static int 
>> migration_completion_precopy(MigrationState *s,
>>      bql_lock();
>>      migration_downtime_start(s);
>>  
>> -    s->vm_old_state = runstate_get();
>> -    global_state_store();
>> -
>> -    ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
>> -    trace_migration_completion_vm_stop(ret);
>> -    if (ret < 0) {
>> -        goto out_unlock;
>> +    if (!migrate_mode_is_cpr(s)) {
>> +        s->vm_old_state = runstate_get();
>> +        global_state_store();
>> +        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
>> +        trace_migration_completion_vm_stop(ret);
>> +        if (ret < 0) {
>> +            goto out_unlock;
>> +        }
>>      }
>>  
>>      ret = migration_maybe_pause(s, current_active_state,
>> @@ -3576,6 +3582,7 @@ void migrate_fd_connect(MigrationState *s, Error 
>> *error_in)
>>      Error *local_err = NULL;
>>      uint64_t rate_limit;
>>      bool resume = s->state == MIGRATION_STATUS_POSTCOPY_PAUSED;
>> +    int ret;
>>  
>>      /*
>>       * If there's a previous error, free it and prepare for another one.
>> @@ -3651,6 +3658,17 @@ void migrate_fd_connect(MigrationState *s, Error 
>> *error_in)
>>          goto fail;
>>      }
>>  
>> +    if (migrate_mode_is_cpr(s)) {
>> +        s->vm_old_state = runstate_get();
>> +        global_state_store();
>> +        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
>> +        trace_migration_completion_vm_stop(ret);
>> +        if (ret < 0) {
>> +            error_setg(&local_err, "migration_stop_vm failed, error %d", 
>> -ret);
>> +            goto fail;
>> +        }
>> +    }
> 
> Could we have a helper function for the shared codes?

Will do.

> How about postcopy?  I know it's nonsense to enable postcopy for cpr.. but
> iiuc we don't yet forbid an user doing so.  Maybe we should?

I will assert that mode != cpr in the postcopy path instead, to prevent any 
nonsense.

- Steve

>> +
>>      if (migrate_background_snapshot()) {
>>          qemu_thread_create(&s->thread, "bg_snapshot",
>>                  bg_migration_thread, s, QEMU_THREAD_JOINABLE);
>> -- 
>> 1.8.3.1
>>
>