Re: [Qemu-devel] [PATCH] kvm: Move kvm_allows_irq0_override() to target-i386

[Avi Kivity]

On 07/23/2012 03:25 PM, Peter Maydell wrote:
> On 23 July 2012 13:18, Avi Kivity <address@hidden> wrote:
>>  While you don't have an irqchip, you do have asynchronous interrupt
>> injection, yes?  That's what irqchip really is all about.
> 
> This seems an odd point of view -- async interrupt injection
> doesn't have anything to do with whether we're modelling
> the irqchip in the kernel or in QEMU, I thought...

It does on x86.  The relationship between the APIC and the core is
synchronous - the APIC presents the interrupt, the core grabs is when it
is ready (interrupt flag, etc.) and signals the APIC it has done so.
The APIC then clears the interrupt from the interrupt request register
and sets it in the interrupt status register.  This sequence has to be
done while the vcpu is stopped, since we don't have access to the
interrupt flag otherwise.

-- 
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