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-level 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 code paths in 35 them are very performance critical. 36