Re: KVM in-kernel APIC update

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Ingo Molnar wrote:
> there is a remote possibility that some OSs depend on certain devices 
> being level-triggered: for example if you get an IRQ from a 
> level-triggered device and _dont_ deassert that signal from the IRQ 
> handler (intentionally so), then the semantics of current hardware will 
> cause a second interrupt to be sent by the PIC, after the APIC message 
> has been EOI-ed in the local APIC. While such "repeat interrupts" would 
> be pure madness to rely on i think, i'm not sure it's not being done. 
> Note that if the same IO-APIC pin is set up to detect edges then not 
> deasserting the signal would not cause a 'repeat interrupt'. Whether 
> such accurate emulation of signalling is needed depends on the hardware 
> semantics of the devices we emulate.
>
>   

Don't all OSes heavily depend on level-triggered interrupts for irq line 
sharing?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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