Hi, I´m doing some research on Nested Virtualization with KVM and Xen. My cpu on bare-metal system is a Opteron_G4 --> (AMD Opteron 4280). qemu-version 1.0; libvirt 0.9.12 For nesting KVM in KVM I´m adding the <cpu mode='host-passthrough'/> command to the XML-File of the VM on Layer 0. So I´m able to install KVM in KVM and create nested guests at Layer 2. L2 --> Nested VM L1 --> KVM / XEN L0 --> KVM If i try the same with installing Xen in the VM on Layer 1 Xen don´t boot and I get following error: Panic on CPU 0: GENERAL PROTECTION FAULT [error_code=0000] If I remove <cpu mode='host-passthrough'/> command from the VM´s XML Xen boot is successful and Nesting Xen in KVM works! May this problem depends on the following problem --> https://bugzilla.redhat.com/show_bug.cgi?id=804224