Paravirtualized

Paravirtualization is a virtualization approach in which the guest operating system is modified to run in cooperation with a hypervisor. Instead of fully emulating hardware, the guest uses specialized interfaces, known as hypercalls and paravirtualized drivers, to request services such as memory management, I/O, and interrupts from the hypervisor. Because the guest is aware of the virtualization layer, the hypervisor can avoid costly traps and emulation, yielding lower overhead and often higher performance on CPUs without advanced hardware support.

In a paravirtualized system, the guest kernel and drivers are adapted to operate with the hypervisor’s interface. Virtual devices are typically provided by paravirtualized drivers that communicate through hypercalls and shared memory rather than through fully emulated hardware. The approach is closely associated with early Xen deployments, where modified guests (domU) used para-virtual devices. With the rise of hardware-assisted virtualization, many environments moved toward full virtualization, though para-virtualized components and hybrid modes can still be used for performance gains.

Advantages of paravirtualization include reduced overhead, lower context-switch costs, and more efficient I/O handling in certain workloads. Limitations include the need to modify the guest operating system, which reduces portability and complicates support across different distributions and versions. Not all operating systems have readily available para-virtualized builds, and compatibility depends on the hypervisor.

Today, paravirtualization is less common for general-purpose virtualization but persists in some hypervisors as a performance-tuning option or in hybrid PV/HVM configurations. It remains a significant concept in the history of virtualization design and in discussions of hypervisor-guest collaboration strategies.