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