Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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diff --git a/Documentation/virt/paravirt_ops.rst b/Documentation/virt/paravirt_ops.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+============
+Paravirt_ops
+============
+
+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-ops 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 of code paths in
+   them are very performance critical.