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authorLinus Torvalds <torvalds@linux-foundation.org>2015-02-18 09:24:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-18 09:24:01 -0800
commit53861af9a17022898619a2ae4ead0dfc601b7c13 (patch)
treedc11088d9e86fa1d8d8479974864153a8f976897 /Documentation
parent5c2770079fb9b8c5bfb7113d9e76de66e77a0e24 (diff)
parent5b40a7daf51812b35cf05d1601a779a7043f8414 (diff)
Merge tag 'virtio-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux
Pull virtio updates from Rusty Russell: "OK, this has the big virtio 1.0 implementation, as specified by OASIS. On top of tht is the major rework of lguest, to use PCI and virtio 1.0, to double-check the implementation. Then comes the inevitable fixes and cleanups from that work" * tag 'virtio-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux: (80 commits) virtio: don't set VIRTIO_CONFIG_S_DRIVER_OK twice. virtio_net: unconditionally define struct virtio_net_hdr_v1. tools/lguest: don't use legacy definitions for net device in example launcher. virtio: Don't expose legacy net features when VIRTIO_NET_NO_LEGACY defined. tools/lguest: use common error macros in the example launcher. tools/lguest: give virtqueues names for better error messages tools/lguest: more documentation and checking of virtio 1.0 compliance. lguest: don't look in console features to find emerg_wr. tools/lguest: don't start devices until DRIVER_OK status set. tools/lguest: handle indirect partway through chain. tools/lguest: insert driver references from the 1.0 spec (4.1 Virtio Over PCI) tools/lguest: insert device references from the 1.0 spec (4.1 Virtio Over PCI) tools/lguest: rename virtio_pci_cfg_cap field to match spec. tools/lguest: fix features_accepted logic in example launcher. tools/lguest: handle device reset correctly in example launcher. virtual: Documentation: simplify and generalize paravirt_ops.txt lguest: remove NOTIFY call and eventfd facility. lguest: remove NOTIFY facility from demonstration launcher. lguest: use the PCI console device's emerg_wr for early boot messages. lguest: always put console in PCI slot #1. ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ia64/paravirt_ops.txt137
-rw-r--r--Documentation/virtual/00-INDEX3
-rw-r--r--Documentation/virtual/paravirt_ops.txt32
3 files changed, 35 insertions, 137 deletions
diff --git a/Documentation/ia64/paravirt_ops.txt b/Documentation/ia64/paravirt_ops.txt
deleted file mode 100644
index 39ded02ec33f..000000000000
--- a/Documentation/ia64/paravirt_ops.txt
+++ /dev/null
@@ -1,137 +0,0 @@
-Paravirt_ops on IA64
-====================
- 21 May 2008, Isaku Yamahata <yamahata@valinux.co.jp>
-
-
-Introduction
-------------
-The aim of this documentation is to help with maintainability and/or to
-encourage people to use paravirt_ops/IA64.
-
-paravirt_ops (pv_ops in short) is a way for virtualization support of
-Linux kernel on x86. Several ways for virtualization support were
-proposed, paravirt_ops is the winner.
-On the other hand, now there are also several IA64 virtualization
-technologies like kvm/IA64, xen/IA64 and many other academic IA64
-hypervisors so that it is good to add generic virtualization
-infrastructure on Linux/IA64.
-
-
-What is paravirt_ops?
----------------------
-It has been developed on x86 as virtualization support via API, not ABI.
-It allows each hypervisor to override operations which are important for
-hypervisors at API level. And it allows a single kernel binary to run on
-all supported execution environments including native machine.
-Essentially paravirt_ops is a set of function pointers which represent
-operations corresponding to low level sensitive instructions and high
-level functionalities in various area. But one significant difference
-from usual function pointer table is that it allows optimization with
-binary patch. It is because some of these operations are very
-performance sensitive and indirect call overhead is not negligible.
-With binary patch, indirect C function call can be transformed into
-direct C function call or in-place execution to eliminate the overhead.
-
-Thus, operations of paravirt_ops are classified into three categories.
-- simple indirect call
- These operations correspond to high level functionality so 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 instructions. They
- are called frequently and performance critical. So 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.
-
-
-The relation to the IA64 machine vector
----------------------------------------
-Linux/IA64 has the IA64 machine vector functionality which allows the
-kernel to switch implementations (e.g. initialization, ipi, dma api...)
-depending on executing platform.
-We can replace some implementations very easily defining a new machine
-vector. Thus another approach for virtualization support would be
-enhancing the machine vector functionality.
-But paravirt_ops approach was taken because
-- virtualization support needs wider support than machine vector does.
- e.g. low level instruction paravirtualization. It must be
- initialized very early before platform detection.
-
-- virtualization support needs more functionality like binary patch.
- Probably the calling overhead might not be very large compared to the
- emulation overhead of virtualization. However in the native case, the
- overhead should be eliminated completely.
- A single kernel binary should run on each environment including native,
- and the overhead of paravirt_ops on native environment should be as
- small as possible.
-
-- for full virtualization technology, e.g. KVM/IA64 or
- Xen/IA64 HVM domain, the result would be
- (the emulated platform machine vector. probably dig) + (pv_ops).
- This means that the virtualization support layer should be under
- the machine vector layer.
-
-Possibly it might be better to move some function pointers from
-paravirt_ops to machine vector. In fact, Xen domU case utilizes both
-pv_ops and machine vector.
-
-
-IA64 paravirt_ops
------------------
-In this section, the concrete paravirt_ops will be discussed.
-Because of the architecture difference between ia64 and x86, the
-resulting set of functions is very different from x86 pv_ops.
-
-- C function pointer tables
-They are not very performance critical so that simple C indirect
-function call is acceptable. The following structures are defined at
-this moment. For details see linux/include/asm-ia64/paravirt.h
- - struct pv_info
- This structure describes the execution environment.
- - struct pv_init_ops
- This structure describes the various initialization hooks.
- - struct pv_iosapic_ops
- This structure describes hooks to iosapic operations.
- - struct pv_irq_ops
- This structure describes hooks to irq related operations
- - struct pv_time_op
- This structure describes hooks to steal time accounting.
-
-- a set of indirect calls which need optimization
-Currently this class of functions correspond to a subset of IA64
-intrinsics. At this moment the optimization with binary patch isn't
-implemented yet.
-struct pv_cpu_op is defined. For details see
-linux/include/asm-ia64/paravirt_privop.h
-Mostly they correspond to ia64 intrinsics 1-to-1.
-Caveat: Now they are defined as C indirect function pointers, but in
-order to support binary patch optimization, they will be changed
-using GCC extended inline assembly code.
-
-- a set of macros for hand written assembly code (.S files)
-For maintenance purpose, the taken approach for .S files is single
-source code and compile multiple times with different macros definitions.
-Each pv_ops instance must define those macros to compile.
-The important thing here is that sensitive, but non-privileged
-instructions must be paravirtualized and that some privileged
-instructions also need paravirtualization for reasonable performance.
-Developers who modify .S files must be aware of that. At this moment
-an easy checker is implemented to detect paravirtualization breakage.
-But it doesn't cover all the cases.
-
-Sometimes this set of macros is called pv_cpu_asm_op. But there is no
-corresponding structure in the source code.
-Those macros mostly 1:1 correspond to a subset of privileged
-instructions. See linux/include/asm-ia64/native/inst.h.
-And some functions written in assembly also need to be overrided so
-that each pv_ops instance have to define some macros. Again see
-linux/include/asm-ia64/native/inst.h.
-
-
-Those structures must be initialized very early before start_kernel.
-Probably initialized in head.S using multi entry point or some other trick.
-For native case implementation see linux/arch/ia64/kernel/paravirt.c.
diff --git a/Documentation/virtual/00-INDEX b/Documentation/virtual/00-INDEX
index e952d30bbf0f..af0d23968ee7 100644
--- a/Documentation/virtual/00-INDEX
+++ b/Documentation/virtual/00-INDEX
@@ -2,6 +2,9 @@ Virtualization support in the Linux kernel.
00-INDEX
- this file.
+
+paravirt_ops.txt
+ - Describes the Linux kernel pv_ops to support different hypervisors
kvm/
- Kernel Virtual Machine. See also http://linux-kvm.org
uml/
diff --git a/Documentation/virtual/paravirt_ops.txt b/Documentation/virtual/paravirt_ops.txt
new file mode 100644
index 000000000000..d4881c00e339
--- /dev/null
+++ b/Documentation/virtual/paravirt_ops.txt
@@ -0,0 +1,32 @@
+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.

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