qemu-kvm: plan for MSI-X

So, now MSI-X is in upstream qemu. The issue here is that irqchip in kernel is still unsupported. So here's the plan for qemu-kvm:

1. on next merge from qemu.git to qemu.kvm, virtio net will be broken
2. a quick work-around is to replace this line in hw/apic.c:

	msix_supported = 1;
   with
	if (!kvm_enabled() || !qemu_kvm_irqchip_in_kernel())
	   msix_supported = 1;

3. once that is merged, I'll add a patch for kernel msi-x that is qemu-kvm specific.

4. Overall it is unfortunate that we still need to add qemu-kvm specific hacks in new code. Is someone working on upstreaming irqchip btw?

Comments? Avi?

MST