Pervirtualization

Pervirtualization is a term sometimes used to describe a virtualization approach in which a guest operating system is modified to cooperate with a hypervisor through a specialized interface, rather than relying solely on full hardware virtualization. In practice, the term is not widely used in mainstream literature, and many sources refer to the related concept of paravirtualization. The core idea is to reduce virtualization overhead by enabling the guest to run in a hypervisor-aware mode and to replace certain privileged hardware operations with hypervisor calls.

How it works: under pervirtualization, the guest OS is altered to use hypervisor-provided services for critical tasks such as I/O processing and certain memory-management operations. The hypervisor offers a cooperative interface, and devices inside the guest can communicate with the hypervisor through paravirtualized drivers or templates. This cooperation avoids some of the overhead associated with trapping and emulating instructions on every privileged operation.

History and implementations: paravirtualization was popularized in the early 2000s with Xen and other hypervisors that required modified guest kernels. Linux and BSD communities developed paravirtualized drivers to improve performance. Over time, hardware-assisted virtualization and hybrid approaches (including para-virtualized drivers like VirtIO) became more common, reducing the emphasis on fully paravirtualized guests while preserving the performance benefits where supported.

Advantages and limitations: the main benefit is lower overhead and higher I/O efficiency for supported workloads. Limitations include the need for OS modifications or vendor-provided PV modules, potential maintenance and portability challenges, and uneven support across operating systems and distributions.

See also: paravirtualization.