From system dmesg:

[    0.000000] Intel-IOMMU: enabled

From xm dmesg:

(XEN) VMX: Supported advanced features:
(XEN)  - APIC MMIO access virtualisation
(XEN)  - APIC TPR shadow
(XEN)  - Virtual NMI
(XEN)  - MSR direct-access bitmap
(XEN) HVM: ASIDs disabled.
(XEN) HVM: VMX enabled
(XEN) I/O virtualisation disabled