KVMXen

KVMXen is a term used in some discussions and experimental projects to describe an attempted integration between the KVM (Kernel-based Virtual Machine) and Xen virtualization technologies. It is not a formal, widely adopted project with a single specification, and references to KVMXen can denote different approaches rather than one canonical implementation.

KVM and Xen are two mature virtualization stacks. KVM is part of the Linux kernel and uses KVM kernel modules with user-space components such as QEMU to provide hardware-assisted virtualization. Xen is a stand-alone hypervisor with its own architecture, historically employing a privileged domain and support for both paravirtualization and hardware-assisted virtualization. Their designs differ in areas such as device models, memory management, and I/O handling, which affects how any combined effort would be structured.

In practice, discussions about KVMXen have contemplated several architectures. These include running KVM guests within a Xen-controlled environment using nesting or PVH-based integrations, running Xen as a guest under KVM, or establishing a shared interface layer that enables certain features of both ecosystems to be utilized by guests and hypervisors alike.

The potential benefits of such an integration could include smoother migration paths between platforms, more flexible testing environments, and the ability to leverage strengths from both KVM and Xen. However, significant challenges exist, including added system complexity, security boundary concerns, possible performance penalties from nesting, driver and compatibility issues, licensing considerations, and limited community and vendor support.

As of now, KVMXen lacks a standardized specification and is not widely deployed in production. It remains largely experimental, with usage and interpretation varying across sources. Related topics include KVM, Xen, nested virtualization, PVH, and interoperability efforts in virtualization.