Citrix Hypervisor is based on the open-source Xen hypervisor. Citrix Hypervisor 8 runs on the Xen 4.11 hypervisor. This release contains mitigations for the Meltdown and Spectre vulnerabilities. https://tinyurl.com/y88ken4k
Citrix Hypervisor uses paravirtualization and hardware-assisted virtualization, requiring either a modified guest OSs or hardware assisted CPUs (more commonly seen as its less restrictive and hardware assisted CPUs like Intel VT/AMD-V have become standard). The device drivers are provided through a 64-bit Linux-based guest (CentOS) running in a control virtual machine (Dom0).