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

From: Alexander Graf
Subject: Re: [Qemu-ppc] [PATCH v3 1/4] cpus: Define NMI callback
Date: Wed, 11 Jun 2014 14:04:52 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130910 Thunderbird/17.0.9

On 06/11/2014 12:47 PM, Paolo Bonzini wrote:
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.

On PPC every input line to a CPU is a qemu_irq. I don't see how a linking piece between this qemu_irq object and a command line interface is overengineered. Whether the linking piece is "a device you look for and call a function in" or "a machine callback you call" is an implementation detail IMHO.

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.

Yes :).


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