Re: [PATCH V4 06/11] migration: preserve cpu ticks if suspended

[Steven Sistare]

On 8/30/2023 12:47 PM, Peter Xu wrote:
> On Tue, Aug 29, 2023 at 11:18:01AM -0700, Steve Sistare wrote:
>> During RUN_STATE_SUSPENDED, the cpu clock remains enabled, so the
>> timers_state saved to the migration stream is stale, causing time errors
>> in the guest when it wakes from suspend.
> 
> Instead of having this, I'm wondering whether we should just let:
> 
>         ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
> 
> stop the vm for suspended too - I think we reached a consensus that
> SUSPENDED should be treated the same as running here (except the vcpu
> beingg running or not).
> 
> So the more risky change is we should make runstate_is_running() cover
> SUSPENDED, but of course that again can affect many other call sites.. and
> I'm not sure whether it's 100% working everywhere.
> 
> I think I mentioned the other "easier" way, which is to modify
> vm_stop_force_state() to take suspended:
> 
> int vm_stop_force_state(RunState state)
>  {
> -    if (runstate_is_running()) {
> +    if (runstate_is_running() || runstate_is_suspended()) {
>          return vm_stop(state);
> 
> That resides in cpus.c but it really only affects migration, so much less
> risky.  Do you think this should be the better (and correct) way to go?

Hi Peter, thanks for your careful review.  I have some other work to do, but
I will get back to this soon.

- Steve