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?
Paolo