Linux provides support for different hypervisor virtualization technologies. Historically different binary kernels would be required in order to support different hypervisors, this restriction was removed with pv_ops. Linux pv_ops is a virtualization API which enables support for different hypervisors. It allows each hypervisor to override critical operations and allows a single kernel binary to run on all supported execution environments including native machine – without any hypervisors.
pv_ops provides a set of function pointers which represent operations corresponding to low level critical instructions and high level functionalities in various areas. pv-ops allows for optimizations at run time by enabling binary patching of the low-ops critical operations at boot time.
pv_ops operations are classified into three categories:
- simple indirect call
- These operations correspond to high level functionality where it is known that the overhead of indirect call isn’t very important.
- indirect call which allows optimization with binary patch
- Usually these operations correspond to low level critical instructions. They are called frequently and are performance critical. The overhead is very important.
- a set of macros for hand written assembly code
- Hand written assembly codes (.S files) also need paravirtualization because they include sensitive instructions or some of code paths in them are very performance critical.