Re: [Qemu-devel] [PATCH] spapr: support CPU hotplug

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 08/27/2013 06:54 PM, Alexander Graf wrote:
> 
> On 27.08.2013, at 09:41, Alexey Kardashevskiy wrote:
> 
>> On 08/27/2013 05:02 PM, Paolo Bonzini wrote:
>>> Il 27/08/2013 08:37, Alexey Kardashevskiy ha scritto:
>>>>>> So this is here to make sure we don't accidentally get out of halted state by an interrupt on that vcpu. Could you please somehow make that part obvious? Either by adding a comment or by only explicitly masking DEC and EE and a comment :).
>>>>>>
>>>>>>> +    cs->exit_request = 1;
>>>>>>
>>>>>> This should probably be qemu_cpu_kick_self().
>>>>>
>>>>> Uh, no, I don't think so.  This is there purely to make sure we exit
>>>>> the inner loop, and actually test cpu_can_run() which will test
>>>>> halted.  AFAICT qemu_cpu_kick_self() won't do anything similar.
>>>>
>>>> rtas_stop_self() eventually returns to kvm_cpu_exec() which calls
>>>> qemu_cpu_kick_self() and resets cs->exit_request before return so I do not
>>>> really see the difference in behaviour. And actually both ways CPU stops in
>>>> exactly the same way. What do I miss?
>>>
>>> What about TCG?
>>
>> Oh. Right. TCG :(
>>
>> qemu_cpu_kick_self() crashes the guest and cs->exit_request works fine.
>>
>> Why? Both should work? What is the expected behavior here? Thanks.
> 
> Hrm. To me exit_request always was an internal piece of state that the inner loop uses to find out whether to exit, but not something we should randomly set from a device (and hypercalls / rtas calls are very similar to devices). So I would like to not have any code in hw/ that modifies it.
> 
> However, we need the functionality of breaking out of the main loop, I agree.

> Maybe what you are really looking for is
> cpu_interrupt(CPU_INTERRUPT_HALT). That sets halted = 1 and exits the
> main loop, because it's an interrupt.

cpu_interrupt(CPU_INTERRUPT_HALT) works fine for TCG but does not for KVM
(the rtas call returns to the guest and it reports BUG).


-- 
Alexey