Re: [Qemu-devel] [PATCH v1] kvm/x86: Remove Hyper-V SynIC timer stopping

[Paolo Bonzini]

On 14/12/2015 18:01, Andrey Smetanin wrote:
> host                    guest
>                     start periodic stimer
> start periodic timer
> timer expires after 15ms
> send expiration message into guest
> restart periodic timer
>                     ....doing something....
> timer expires again after 15 ms
> msg slot is still not cleared so
> setup ->msg_pending
> restart periodic timer
>                     ....doing something....
>                     process timer msg and clear slot
>                     so ->msg_pending was set:
>                         send EOM into host
> received EOM
> queued call of kvm_hv_process_stimers()
> by KVM_REQ_HV_STIMER
> 
> kvm_hv_process_stimers():
>     ...
>     stimer_stop()
>     if (time_now >= stimer->exp_time)
>             stimer_expiration(stimer);
> But time_now  < stimer->exp_time, so stimer_expiration is not called
> in this case and timer is not restarted. so guest lose timer.

Great, this explains it.

Paolo