Re: in-kernel interrupt controller steering

[Paolo Bonzini <pbonzini@redhat.com>]

> Please go ahead and try to describe an interface the way you envision
> it. It needs to fulfill the following criteria:
> 
>   * different machine models have different interrupt controller
>   types
>   * we need to be able to fetch information from interrupt
>   controllers, this should be as flexible as possible because we
>   don't know all future state we want to synchronize today
>   * user space creates its virtual representation of an interrupt
>   controller after the vcpus got created
>   * user space needs a token to an interrupt controller, so that we
>   have the possibility to add a second in-kernel irqchip if the need
>   arises
> 
> What the current interface does is:
> 
>   SET_IRQCHIP_TYPE:
> 
>     * declare CPUs as listeners to a specific irqchip bus
>     * set the path that interrupt injection takes (this could
>     probably be changed to dynamic lookups though, based on device
>     tokens)
> 
>   CREATE_DEVICE:
> 
>     * spawn one or multiple in-kernel irqchip devices that hook up to
>     CPUs using the irqchip bus
>     * tell user space a token to access this irqchip
> 
> I really don't see why you wouldn't want to have that split.

I agree.  But is the device really being created at CREATE_DEVICE time?
What happens if you create N CPUs and N-1 irqchips?

On x86, the LAPIC is created magically together with the VCPU.

Paolo