Using kvm to run xen guests without xen

The inclusion of the Kernel Virtual Machine (KVM) driver in Linux 2.6.20 has dramatically improved Linux’s ability to act as a hypervisor. Previously, Linux was only capable of running UML guests and contain-ers. KVM adds support for running unmodified x86 operating systems using hardware-based virtualization. The current KVM user community is limited by the availability of said hardware. The Xen hypervisor, which can also run unmodified op-erating systems with hardware virtualization, introduced a paravirtual ABI for running modified operating sys-tems such as Linux, Netware, FreeBSD, and OpenSo-laris. This ABI not only provides a performance advan-tage over running unmodified guests, it does not require any hardware support, increasing the number of users that can utilize the technology. The modifications to the Linux kernel to support the Xen paravirtual ABI are in-cluded in some Linux distributions, but have not been merged into mainline Linux kernels. This paper will describe the modifications to KVM required to support the Xen paravirtual ABI and a new module, kvm-xen, implementing the requisite hypervisor-half of the ABI. Through these modifica-tions, Linux can add to its list of supported guests all of the paravirtual operating systems currently supported by Xen. We will also evaluate the performance of a Xeno-Linux guest running under the Linux hypervisor to com-pare Linux’s ability to act as a hypervisor versus a more traditional hypervisor such as Xen.