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[Qemu-devel] Re: [RFC] KVM: PPC: Add level based interrupt logic


From: Alexander Graf
Subject: [Qemu-devel] Re: [RFC] KVM: PPC: Add level based interrupt logic
Date: Wed, 1 Sep 2010 13:58:43 +0200

On 01.09.2010, at 13:56, Avi Kivity wrote:

> On 09/01/2010 02:47 PM, Alexander Graf wrote:
>> On 01.09.2010, at 13:45, Avi Kivity wrote:
>> 
>>> On 09/01/2010 12:38 PM, Alexander Graf wrote:
>>>> On 01.09.2010, at 09:41, Avi Kivity wrote:
>>>> 
>>>>> On 08/31/2010 01:07 PM, Alexander Graf wrote:
>>>>>> KVM on PowerPC used to have completely broken interrupt logic. Usually,
>>>>>> interrupts work by having a PIC that pulls a line up/down, so the CPU 
>>>>>> knows
>>>>>> that an interrupt is active. This line stays active until some action is
>>>>>> done to the PIC to release the line.
>>>>>> 
>>>>>> On KVM for PPC, we just checked if there was an interrupt pending and 
>>>>>> pulled
>>>>>> a line in the kernel module. We never released it though, hoping that 
>>>>>> kernel
>>>>>> space would just declare an interrupt as released when injected - which 
>>>>>> is
>>>>>> wrong.
>>>>>> 
>>>>>> To fix this, we need to completely redesign the interrupt injection 
>>>>>> logic.
>>>>>> Whenever an interrupt line gets triggered, we need to notify kernel space
>>>>>> that the line is up. Whenever it gets released, we do the same. This way
>>>>>> we can assure that the interrupt state is always known to kernel space.
>>>>>> 
>>>>>> This fixes random stalls in KVM guests on PowerPC that were waiting for
>>>>>> an interrupt while everyone else thought they received it already.
>>>>> This is more or less equivalent to KVM_IRQ_LINE.
>>>> My question was if you think the internal C interface is generic enough or 
>>>> if it needs a lot more magic for x86 anyways :).
>>>> 
>>> So you noticed I avoided it.  Well, being forced to look, I don't think 
>>> it's worthwhile to try to be generic here.  Both the PIC<->APIC and the 
>>> APIC<->core interfaces are too complicated to be modelled by a single line.
>> Makes sense. Well, I guess it doesn't hurt to have the interface as is and 
>> only implement it for PPC for now.
>> 
>> 
> 
> Why not limit it to ppc?  Someone might call it by accident.

How would you model it? Call kvm_arch_set_interrupt in hw/ppc.c? Which header 
would I define the call in?


Alex




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