Re: [Qemu-devel] latest rc: virtio-blk hangs forever after migration

[Marcin Gibuła]

W dniu 2014-07-31 13:27, Marcin Gibuła pisze:
> > > Can you dump *env before and after the call to kvm_arch_get_registers?
> >
> > Yes, but it seems they are equal - I used memcmp() to compare them. Is
> > there any other side effect that cpu_synchronize_all_states() may have?
>
> I think I found it.
>
> The reason for hang is, because when second call to
> kvm_arch_get_registers() is skipped, it also skips kvm_get_apic() which
> updates cpu->apic_state.

Paolo,

is this analysis deep enough for you? I don't know if that can be fixed 
with existing api as cpu_synchronize_all_states() is all or nothing kind 
of stuff.

Kvmclock needs it only to read current cpu registers, so syncing 
everything is not really necessary. Perhaps exporting one of 
kvm_arch_get_* would be enough. And it wouldn't mess with lazy get/put.

On the other hand, if in future any other driver adds 
cpu_synchronize_all_states() in its change state callback it could 
result in same error so perhaps more generic approach is needed.

--
mg