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-level 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 code paths in them are very performance critical.