Re: [libvirt] [PATCHv3 1/6] conf: add <irqchip mode> to <features>

On 26/04/2017 11:36, Peter Xu wrote: >> Possible values are off, split or on. > Hi, Ján, > > Thanks you for cced me. One tiny comment on irqchip mode... > > Here could user specify irqchip=off from libvirt side? IIUC that might > be dangerous since userspace APIC should only be for debugging purpose > (when kernel-irqchip=off, we'll be using userspace APIC, not kernel > one, and iirc Paolo mentioned known bugs in userspace APIC). So imho > we'd better not allow user to use "off", but only "on" and "split". > > CCing Paolo here in case he has any comment on this. Allowing "off" may be okay as long as it taints the domain.

In the end, irqchip mode is a feature of the APIC/IOAPIC/PIC/PIT, and even more specifically: - for kernel-irqchip=off, the distinguishing feature is in-kernel vs. userspace APIC. - for kernel-irqchip=split, what we really care about is userspace IOAPIC. So perhaps another choice for the XML is: <features> <apic driver='qemu|kvm'/> <ioapic driver='qemu|kvm'/> </features> where (apic:qemu,ioapic:kvm) is invalid?