On Wed, Apr 26, 2017 at 04:19:07PM +0200, Paolo Bonzini wrote:
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.
If it's only useful for debugging, I can drop "off" from the XML completely.
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?
And if apic:qemu,ioapic:qemu is only for debugging, the <apic> element can be dropped too. 'ioapic' is also more specific (so if kernel-irqchip starts to be useful on other archs, libvirt might need a new element?). I'm considering sticking the attribute to the already-existing apic element: <apic mode='kernel|split'/> But I don't really like any of the options. Jan
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