Re: [PATCH V4 05/11] migration: preserve suspended for bg_migration

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 29, 2023 at 11:18:00AM -0700, Steve Sistare wrote:
> Do not wake a suspended guest during bg_migration.
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  migration/migration.c | 12 +++++-------
>  softmmu/runstate.c    |  1 +
>  2 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index a9ecb66..303d5a6 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3064,7 +3064,9 @@ static void bg_migration_vm_start_bh(void *opaque)
>      qemu_bh_delete(s->vm_start_bh);
>      s->vm_start_bh = NULL;
>  
> -    vm_start();
> +    if (!runstate_check(RUN_STATE_SUSPENDED)) {
> +        vm_start();
> +    }
>      s->downtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - s->downtime_start;
>  }
>  
> @@ -3134,16 +3136,12 @@ static void *bg_migration_thread(void *opaque)
>  
>      qemu_mutex_lock_iothread();
>  
> -    /*
> -     * If VM is currently in suspended state, then, to make a valid runstate
> -     * transition in vm_stop_force_state() we need to wakeup it up.
> -     */
> -    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
>      s->vm_old_state = runstate_get();
>  
>      global_state_store();
>      /* Forcibly stop VM before saving state of vCPUs and devices */
> -    if (vm_stop_force_state(RUN_STATE_PAUSED)) {
> +    if (!runstate_check(RUN_STATE_SUSPENDED) &&
> +        vm_stop_force_state(RUN_STATE_PAUSED)) {

IIUC we need the vm_stop even for SUSPENDED?  I think we need to make sure
all backends are stopped before we start wr-protect the guest pages, so
when wr-protect happens the guest pages should be in a consistent state.

I'd think it proper to juse reuse the helper you introduced in the previous
patches, but maybe you have a reason to not do so (I didn't see it
mentioned anywhere, though)?

>          goto fail;
>      }
>      /*
> diff --git a/softmmu/runstate.c b/softmmu/runstate.c
> index 21d7407..4417527 100644
> --- a/softmmu/runstate.c
> +++ b/softmmu/runstate.c
> @@ -163,6 +163,7 @@ static const RunStateTransition runstate_transitions_def[] = {
>      { RUN_STATE_SUSPENDED, RUN_STATE_FINISH_MIGRATE },
>      { RUN_STATE_SUSPENDED, RUN_STATE_PRELAUNCH },
>      { RUN_STATE_SUSPENDED, RUN_STATE_COLO},
> +    { RUN_STATE_SUSPENDED, RUN_STATE_PAUSED },
>  
>      { RUN_STATE_WATCHDOG, RUN_STATE_RUNNING },
>      { RUN_STATE_WATCHDOG, RUN_STATE_FINISH_MIGRATE },
> -- 
> 1.8.3.1
> 

-- 
Peter Xu