Re: [PATCH] kvm uses smp_call_function_mask() in kvm_flush_remote_tlbs()

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Avi Kivity wrote:
> Carsten Otte wrote:
>   
>> Laurent Vivier wrote:
>>   
>>     
>>> This patches can be applied only on kvm-updates-2.6.24 and kvm-updates-2.6.25
>>> as it needs smp_call_function_mask().
>>>     
>>>       
>> There's one thing I don't understand: How is this locked versus cpu 
>> hotplug? Isn't there an obvious race involved where a cpu unplugged 
>> after cpu_set()?
>>
>>   
>>     
>
> A cpu unplug first evicts all tasks from the victim cpu.  During this 
> process, it calls kvm via a hotplug notifier, which notifier calls 
> vcpu_clear() for all vcpus that are resident on that cpu.  So after it 
> runs, there won't be any vcpus on the dead cpu.
>
> The notifier is called from within stop_machine_run(), which ensures 
> that no task is running on any cpu, so by the time the cpu is being 
> unplugged, any concurrent call to kvm_flush_remote_tlbs() will have ended.
>
> It's a miracle that it works.
>
>   

Miracle indeed.  We need to disable preemption in 
kvm_flush_remote_tlbs(), otherwise the whole story falls apart.


-- 
error compiling committee.c: too many arguments to function


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