Picked up an Antsle device/system designed to host VMs. It comes with Gentoo Linux and runs KVM and Linux LXC images and can run FreeBSD in a KVM VM.
Paved over Gentoo with LinuxMint 18.3 and installed Xen. All runs OK, but wanted to try the same with FreeBSD as the Dom0.
Downloaded and installed the 11.1 Release then followed the instructions for loading and running Xen as a Dom0. When booting up the Xen Hypervisor it panics claiming the IOMMU isn't present or enabled. There's no option in the BIOS it enable this, but clearly it's present and enabled since Xen under LinuxMint ran.
(In reply to Bob Nestor from comment #0)
I suspect this is because Xen on FreeBSD is running in PVH Mode, thus requiring not just VT-x, but also support for VT-d.
I suspect Sydney Meyer's analysis is correct. From what I can find out about the SOC implementation used on the Antsle it only supports VT-x and doesn't appear to have implemented the VT-d features.
AFAICT none of the Atom C processors support VT-d, so you won't be able to run a FreeBSD/Xen Dom0. Kind of surprising that such hardware is sold as "virtualisation specific" when it's missing such a basic hardware virtualisation feature.
FWIW, if you are searching for a compact virtualization server I would recommend the Intel NUC boxes, they are cheap and most of them (the ones based on the Core i CPUs) have VT-d support.