[chrismsnz]

OpenBSD has had VirtIO (supported by KVM, VMWare and now virtualbox too) guest support for a while now.

AWS uses Xen and domU support is a lot more invasive - OpenBSD had supported it in the past but I believe it was dropped?

[justincormack]

Well PV domU support is more invasive, but HVM is not (it is just like kvm), and Amazon supports both. The middle ground is the pvhvm mode which requires some Xen drivers for additional support, rather than the virtio drivers that kvm/bhyve use - Xen has a different driver model.