1Paravirt_ops
2============
3
4Linux provides support for different hypervisor virtualization technologies.
5Historically different binary kernels would be required in order to support
6different hypervisors, this restriction was removed with pv_ops.
7Linux pv_ops is a virtualization API which enables support for different
8hypervisors. It allows each hypervisor to override critical operations and
9allows a single kernel binary to run on all supported execution environments
10including native machine -- without any hypervisors.
11
12pv_ops provides a set of function pointers which represent operations
13corresponding to low level critical instructions and high level
14functionalities in various areas. pv-ops allows for optimizations at run
15time by enabling binary patching of the low-ops critical operations
16at boot time.
17
18pv_ops operations are classified into three categories:
19
20- simple indirect call
21  These operations correspond to high level functionality where it is
22  known that the overhead of indirect call isn't very important.
23
24- indirect call which allows optimization with binary patch
25  Usually these operations correspond to low level critical instructions. They
26  are called frequently and are performance critical. The overhead is
27  very important.
28
29- a set of macros for hand written assembly code
30  Hand written assembly codes (.S files) also need paravirtualization
31  because they include sensitive instructions or some of code paths in
32  them are very performance critical.
33