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

[Alexander Graf]

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 :).


Alex