Add iommu device when VM configured with > 255 vcpus

Hi All, I vaguely recall a discussion about $subject, but can't find it now. Perhaps buried in another thread. The topic has been raised internally again, and I'd like to gauge the community's interest in automatically adding the necessary devices/config when user has specified vcpus > 255. The comparison for prior art is a bit of a stretch, but we e.g. add <audio type='spice'/> when spice graphics is configured. I know libvirt has generally tried to avoid policy decisions, but it's not clear to me where we stand with cases such as this, where every x86 VM with > 255 vcpus needs a similarly configured iommu. Regards, Jim