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Subject: Re: [Qemu-devel] latest rc: virtio-blk hangs forever after migration
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To: Paolo Bonzini <pbonzini@redhat.com>, Andrey Korolyov <andrey@xdel.ru>
Cc: Amit Shah <amit.shah@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Fam Zheng <famz@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

W dniu 2014-07-31 13:27, Marcin Gibu=C5=82a 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=20
with existing api as cpu_synchronize_all_states() is all or nothing kind=20
of stuff.

Kvmclock needs it only to read current cpu registers, so syncing=20
everything is not really necessary. Perhaps exporting one of=20
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=20
cpu_synchronize_all_states() in its change state callback it could=20
result in same error so perhaps more generic approach is needed.

--=20
mg