Re: [PATCH V6 03/14] cpus: stop vm in suspended runstate

[Peter Xu]

On Thu, Nov 30, 2023 at 01:37:16PM -0800, Steve Sistare wrote:
> Currently, a vm in the suspended state is not completely stopped.  The VCPUs
> have been paused, but the cpu clock still runs, and runstate notifiers for
> the transition to stopped have not been called.  This causes problems for
> live migration.  Stale cpu timers_state is saved to the migration stream,
> causing time errors in the guest when it wakes from suspend, and state that
> would have been modified by runstate notifiers is wrong.
> 
> Modify vm_stop to completely stop the vm if the current state is suspended,
> transition to RUN_STATE_PAUSED, and remember that the machine was suspended.
> Modify vm_start to restore the suspended state.
> 
> This affects all callers of vm_stop and vm_start, notably, the qapi stop and
> cont commands.  For example:
> 
>     (qemu) info status
>     VM status: paused (suspended)
> 
>     (qemu) stop
>     (qemu) info status
>     VM status: paused
> 
>     (qemu) cont
>     (qemu) info status
>     VM status: paused (suspended)
> 
>     (qemu) system_wakeup
>     (qemu) info status
>     VM status: running

So system_wakeup for a stopped (but used to be suspended) VM will fail
directly, not touching vm_was_suspended.  It's not mentioned here, but that
behavior makes sense to me.

> 
> Suggested-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Since you touched qapi/, please copy maintainers too.  I've copied Markus
and Eric in this reply.

I also have some nitpicks which may not affect the R-b, please see below.

> ---
>  include/sysemu/runstate.h |  5 +++++
>  qapi/misc.json            | 10 ++++++++--
>  system/cpus.c             | 19 ++++++++++++++-----
>  system/runstate.c         |  3 +++
>  4 files changed, 30 insertions(+), 7 deletions(-)
> 
> diff --git a/include/sysemu/runstate.h b/include/sysemu/runstate.h
> index f6a337b..1d6828f 100644
> --- a/include/sysemu/runstate.h
> +++ b/include/sysemu/runstate.h
> @@ -40,6 +40,11 @@ static inline bool shutdown_caused_by_guest(ShutdownCause 
> cause)
>      return cause >= SHUTDOWN_CAUSE_GUEST_SHUTDOWN;
>  }
>  
> +static inline bool runstate_is_started(RunState state)

Would runstate_has_vm_running() sound better?  It is a bit awkward when
saying something like "start a runstate".

> +{
> +    return state == RUN_STATE_RUNNING || state == RUN_STATE_SUSPENDED;
> +}
> +
>  void vm_start(void);
>  
>  /**
> diff --git a/qapi/misc.json b/qapi/misc.json
> index cda2eff..efb8d44 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -134,7 +134,7 @@
>  ##
>  # @stop:
>  #
> -# Stop all guest VCPU execution.
> +# Stop all guest VCPU and VM execution.
>  #
>  # Since: 0.14
>  #
> @@ -143,6 +143,9 @@
>  #     the guest remains paused once migration finishes, as if the -S
>  #     option was passed on the command line.
>  #
> +#     In the "suspended" state, it will completely stop the VM and
> +#     cause a transition to the "paused" state. (Since 9.0)
> +#
>  # Example:
>  #
>  # -> { "execute": "stop" }
> @@ -153,7 +156,7 @@
>  ##
>  # @cont:
>  #
> -# Resume guest VCPU execution.
> +# Resume guest VCPU and VM execution.
>  #
>  # Since: 0.14
>  #
> @@ -165,6 +168,9 @@
>  #     guest starts once migration finishes, removing the effect of the
>  #     -S command line option if it was passed.
>  #
> +#     If the VM was previously suspended, and not been reset or woken,
> +#     this command will transition back to the "suspended" state. (Since 9.0)
> +#
>  # Example:
>  #
>  # -> { "execute": "cont" }
> diff --git a/system/cpus.c b/system/cpus.c
> index ef7a0d3..cbc6d6d 100644
> --- a/system/cpus.c
> +++ b/system/cpus.c
> @@ -277,11 +277,15 @@ bool vm_get_suspended(void)
>  static int do_vm_stop(RunState state, bool send_stop)
>  {
>      int ret = 0;
> +    RunState oldstate = runstate_get();
>  
> -    if (runstate_is_running()) {
> +    if (runstate_is_started(oldstate)) {
> +        vm_was_suspended = (oldstate == RUN_STATE_SUSPENDED);
>          runstate_set(state);
>          cpu_disable_ticks();
> -        pause_all_vcpus();
> +        if (oldstate == RUN_STATE_RUNNING) {
> +            pause_all_vcpus();
> +        }
>          vm_state_notify(0, state);
>          if (send_stop) {
>              qapi_event_send_stop();
> @@ -736,8 +740,13 @@ int vm_prepare_start(bool step_pending, RunState state)
>  
>  void vm_start(void)
>  {
> -    if (!vm_prepare_start(false, RUN_STATE_RUNNING)) {
> -        resume_all_vcpus();
> +    RunState state = vm_was_suspended ? RUN_STATE_SUSPENDED : 
> RUN_STATE_RUNNING;
> +
> +    if (!vm_prepare_start(false, state)) {
> +        if (state == RUN_STATE_RUNNING) {
> +            resume_all_vcpus();
> +        }
> +        vm_was_suspended = false;
>      }
>  }
>  
> @@ -745,7 +754,7 @@ void vm_start(void)
>     current state is forgotten forever */
>  int vm_stop_force_state(RunState state)
>  {
> -    if (runstate_is_running()) {
> +    if (runstate_is_started(runstate_get())) {
>          return vm_stop(state);
>      } else {
>          int ret;
> diff --git a/system/runstate.c b/system/runstate.c
> index ea9d6c2..e2fa204 100644
> --- a/system/runstate.c
> +++ b/system/runstate.c
> @@ -108,6 +108,7 @@ static const RunStateTransition 
> runstate_transitions_def[] = {
>      { RUN_STATE_PAUSED, RUN_STATE_POSTMIGRATE },
>      { RUN_STATE_PAUSED, RUN_STATE_PRELAUNCH },
>      { RUN_STATE_PAUSED, RUN_STATE_COLO},
> +    { RUN_STATE_PAUSED, RUN_STATE_SUSPENDED},
>  
>      { RUN_STATE_POSTMIGRATE, RUN_STATE_RUNNING },
>      { RUN_STATE_POSTMIGRATE, RUN_STATE_FINISH_MIGRATE },
> @@ -161,6 +162,7 @@ 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 },
> @@ -502,6 +504,7 @@ void qemu_system_reset(ShutdownCause reason)
>          qapi_event_send_reset(shutdown_caused_by_guest(reason), reason);
>      }
>      cpu_synchronize_all_post_reset();
> +    vm_set_suspended(false);
>  }
>  
>  /*
> -- 
> 1.8.3.1
> 

-- 
Peter Xu