Re: [Qemu-devel] [PATCH v3 1/4] cpus: Define NMI callback

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/06/2014 10:42, Alexander Graf ha scritto:
>
> On 11.06.14 10:37, Paolo Bonzini wrote:
>> Il 11/06/2014 10:29, Alexander Graf ha scritto:
>>>>
>>>> But right now inject-nmi was a CPU-specific interface and whoever
>>>> needs something different will have to find a way.
>>>>
>>>> You could argue that Alexey does need something different thanks to
>>>> his need to inject the NMI on all CPUs.
>>>>
>>>> What about an NMIMonitorHandler interface that takes a Monitor*, and
>>>> then you iterate on all of /machine looking for implementors of the
>>>> interface?  Then -M mac99 can add it to the MPIC, -M spapr can just
>>>> ignore the Monitor*, and i386/s390 can look at the current CPU.
>>>
>>> I think modeling a button is easier and closer to what you'd actually
>>> get on real hardware.
>>
>> What is a button?  It certainly doesn't have any evdev support in Linux.
>
> It's a device that links a qemu_irq line and implements an interface to
> call it.

That seems awfully overengineered.

>> The NMI button is just something that closes a circuit.  Whoever is
>> attached to that circuit reacts, in QEMU that's whoever implements an
>> NMIMonitorHandler.  The Monitor* is just for backwards HMP compatibility.
>
> I think the only major difference in thinking we have here is that I
> don't think it's necessary to maintain HMP compatibility for this debug
> feature that maybe 2 people in the world ever used ;).

Ok, I can buy removing the support for CPU != 0.  But still, the 
overengineering remains.

If Alexey needs to trigger the NMI on all CPUs, simply moving the new 
method from CPU to Machine, and blindly using first_cpu in s390 and x86 
makes the most sense.

Paolo