Re: [RFC][PATCH] qemu-kvm: Introduce writeback scope for cpu_synchronize_state

[Avi Kivity <avi@redhat.com>]

On 11/17/2009 03:05 PM, Jan Kiszka wrote:
>
>> Problem is, the inject channels are implied (APIC messages in smp
>> guests).  Documentation is good, but if we can avoid it that's better.
>>
>> Note the only way to rmw vcpu events during smp is pausing the guest,
>> because of this race.
>>      
> That's what qemu does on reset and load.
>    

These aren't rmw.

> The alternative would be a complex get&lock/put&unlock + a queue for
> async events during the lock + an option to ignore what was queued when
> doing a true reset. Back to square #1: we would still need the proposed
> high-level interface to communicate the difference between replay and
> drop queue.
>    

There's no need for get+lock / put+unlock; a normal get/put with the 
addition that get flushes the queue suffices.  To make sure queued 
events don't affect set you need to stop the entire VM before setting 
state, but you need to do that anyway for non-rmw writes.

-- 
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