1.. SPDX-License-Identifier: GPL-2.0
2
3============
4Paravirt_ops
5============
6
7Linux provides support for different hypervisor virtualization technologies.
8Historically different binary kernels would be required in order to support
9different hypervisors, this restriction was removed with pv_ops.
10Linux pv_ops is a virtualization API which enables support for different
11hypervisors. It allows each hypervisor to override critical operations and
12allows a single kernel binary to run on all supported execution environments
13including native machine -- without any hypervisors.
14
15pv_ops provides a set of function pointers which represent operations
16corresponding to low level critical instructions and high level
17functionalities in various areas. pv-ops allows for optimizations at run
18time by enabling binary patching of the low-ops critical operations
19at boot time.
20
21pv_ops operations are classified into three categories:
22
23- simple indirect call
24   These operations correspond to high level functionality where it is
25   known that the overhead of indirect call isn't very important.
26
27- indirect call which allows optimization with binary patch
28   Usually these operations correspond to low level critical instructions. They
29   are called frequently and are performance critical. The overhead is
30   very important.
31
32- a set of macros for hand written assembly code
33   Hand written assembly codes (.S files) also need paravirtualization
34   because they include sensitive instructions or some of code paths in
35   them are very performance critical.
36