Re: [PATCH V5 02/12] cpus: stop vm in suspended state

[Fabiano Rosas <farosas@suse.de>]

Peter Xu <peterx@redhat.com> writes:

> On Mon, Nov 13, 2023 at 10:33:50AM -0800, Steve Sistare wrote:
>> 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.  Modify vm_stop_force_state to
>> completely stop the vm if the current state is suspended, to be called for
>> live migration and snapshots.
>> 
>> Suggested-by: Peter Xu <peterx@redhat.com>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  system/cpus.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>> 
>> diff --git a/system/cpus.c b/system/cpus.c
>> index f72c4be..c772708 100644
>> --- a/system/cpus.c
>> +++ b/system/cpus.c
>> @@ -255,6 +255,8 @@ void cpu_interrupt(CPUState *cpu, int mask)
>>  static int do_vm_stop(RunState state, bool send_stop, bool force)
>>  {
>>      int ret = 0;
>> +    bool running = runstate_is_running();
>> +    bool suspended = runstate_check(RUN_STATE_SUSPENDED);
>>  
>>      if (qemu_in_vcpu_thread()) {
>>          qemu_system_vmstop_request_prepare();
>> @@ -267,10 +269,12 @@ static int do_vm_stop(RunState state, bool send_stop, bool force)
>>          return 0;
>>      }
>>  
>> -    if (runstate_is_running()) {
>> +    if (running || (suspended && force)) {
>>          runstate_set(state);
>>          cpu_disable_ticks();
>
> Not directly relevant, but this is weird that I just notice.
>
> If we disable ticks before stopping vCPUs, IIUC it means vcpus can see
> stall ticks.  I checked the vm_start() and indeed that one did it in the
> other way round: we'll stop vCPUs before stopping the ticks.
>
>> -        pause_all_vcpus();
>> +        if (running) {
>> +            pause_all_vcpus();
>> +        }
>>          vm_state_notify(0, state);
>>          if (send_stop) {
>>              qapi_event_send_stop();
>
> IIUC the "force" is not actually needed.  It's only used when SUSPENDED,
> right?

That's the overloading I'm complaining about. We're using "force" to say
both: "include suspended" and: "set the state". This is basically taking
knowledge from the callsite being the migration code and encoding it in
that flag.

I'd prefer something like:

static int do_vm_stop(RunState state, bool send_stop, bool set_state,
                      bool include_suspended);