Hmm it works for me on Xen 4.10 (I don't normally use xen but I installed it to check for you)
(XEN) AMD-Vi: Disabled HAP memory map sharing with IOMMU (XEN) AMD-Vi: IOMMU 0 Enabled. (XEN) I/O virtualisation enabled (XEN) - Dom0 mode: Strict (XEN) Interrupt remapping enabled
Btw does anyone know what the difference is between strict and relaxed dom0 mode?