Re: [Qemu-devel] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ support

[Alexander Graf]

On 24.06.2013, at 16:31, Anthony Liguori wrote:

> "Michael S. Tsirkin" <address@hidden> writes:
> 
>> On Mon, Jun 24, 2013 at 08:34:52AM -0500, Anthony Liguori wrote:
>>> Gleb Natapov <address@hidden> writes:
>>> 
>>> Isn't this more or less what Avi's previous proposal was around changing
>>> the APIC interfaces to userspace?
>>> 
>>> Regards,
>>> 
>>> Anthony Liguori
>> 
>> While that's not very elegant, I think we can use the existing
>> interface for this: just encode things in a fake
>> "msi message" in the format that kernel expects.
> 
> This is, in fact, exactly what we do today.  The MSI interfaces aren't
> for MSI.  They are for sending messages to the APIC bus.  What we should
> do is:
> 
> #define KVM_SIGNAL_LAPIC      KVM_SIGNAL_MSI
> #define KVM_IRQ_ROUTING_LAPIC KVM_IRQ_ROUTING_MSI
> 
> And switch to using the new #defines in QEMU.  That would make it more
> obvious where we need to refactor things.  We currently hard code
> routing via a local APIC with MSI.  We need to change this into a bus
> specific function that can choose the right interface.
> 
> I think Power is fine with just doing all routing through the irqchip
> interface.  We may need other routing interfaces for other architectures
> though.

I'm not quite sure what problem exactly you're trying to solve here. The main 
user of MSI injects through irqfd are in the kernel and definitely want a fast 
path to inject those without any involvement of QEMU at all.


Alex