Introduction to Virtual Machines Michael Jantz Acknowledgements - - PowerPoint PPT Presentation

Introduction to Virtual Machines

Michael Jantz

Acknowledgements

• Slides adapted from Chapter 1 in Virtual

Machines: Versatile Platforms for Systems and Processes by James E. Smith and Ravi Nair

• Credit to Prasad A. Kulkarni – some slides

were borrowed from his course on Virtual Machines at the University of Kansas

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Introduction to Virtual Machines

• Abstraction and interfaces
• Virtualization
• Computer system architecture
• Process virtual machines
• System virtual machines

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Abstraction

• Mechanism to manage complexity in

computer systems.

• Partitions design of a system into levels
• Allows higher levels to ignore the

implementation details of lower levels

4

Interfaces

• Define the communication b/w two entities
• Hierarchical relationship
• Linear relationship
• Software can run on any machine

supporting a compatible interface

5

PowerPC MacOS MacIntosh apps. x86 Linux Linux apps x86 Windows Windows apps.

Interfaces: Advantages

• Allows de-coupling of design tasks
• Work on different components can progress

independently

• Helps manage system complexity
• Each component provides an abstraction of

itself to the outside world

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Interfaces: Disadvantages

• Limit flexibility
• Developers must work within the constraints
• f the interface
• Can be confining
• ARM binaries on x86 machine?
• Windows applications on Linux?

7

MacOS MacIntosh apps x86 x86 Windows apps. Linux

Interfaces: Disadvantages

• Inhibits innovation
• Hard to change instruction sets
• Application software cannot directly exploit

microprocessor features

• Software is supposed to be architecture

independent!

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Virtualization

• Map the interface of one system to a real

system that actually implements it

• Removes constraints imposed by interfaces
• Improves availability of application software
• Removes the assumption of a single regime,

improves security and failure isolation

• Provide a different view to a particular

computer resource

• Not necessarily a simpler view

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Virtualization

• Creates an isomorphism that maps a

virtual guest to a real host

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Si S Si ' S

j'

Guest Host

V( S

i)

V(S

j)

e(S

i)

e '(Si')

j

Virtualization vs. Abstraction

• Virtualization does not necessarily hide details

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file file virtualization

Virtual Machines

• Virtualization applied to the entire machine
• Adds a layer of software to a real machine

to support the desired architecture

• Process of virtualization
• Maps virtual resources or state to real

resources

• Uses real machine instructions to carry out

actions specified by the VM instructions

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Benefits of VM's

• Flexibility
• Portability
• Isolation
• Security

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Computer Architecture

• Architecture: functionality and appearance
• f a computer system
• Implementation: embodiment of the

architecture

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Computer Architecture

• Computer systems

consist of:

• Layers of abstraction
• Well-defined interfaces

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I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

The ISA Interface

• Interface between

hardware & software

• Two parts
• System ISA
• User ISA

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I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

The ISA Interface

• System ISA
• Important for OS

developers

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I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

The ABI Interface

• Application Binary

Interface (ABI)

• User ISA + system calls
• Important for compiler

writers

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I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

The API Interface

• Application

Programming Interface (API)

• User ISA + library calls
• Important for

application programmers

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I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

Major Program Interfaces

• ISA – supports all conventional software
• ABI – supports application software only

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System Calls User ISA System ISA

ISA

Application Software Operating System System Calls User ISA System ISA

ABI

Application Software Operating System

Process Virtual Machines

• Supports an individual process
• Run SW for a different OS and different ISA
• Couple at ABI level via runtime system

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Virtualizing Software Application Process Machine OS Hardware

Guest Runtime Host

Application Process

Virtual Machine

Process Virtual Machines

• Guest processes intermingle

with host processes

• Binaries encapsulated by

the runtime

• PVM does not include OS
• Examples:
• Java
• IA-32 EL
• Dynamic optimizers

(dynamo)

HOST OS

Disk

file sharing network communication guest process create host process guest process

runtime runtime

guest process

runtime

host process

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PVM: Multiprogramming

• OS provides PVMs for each application
• System calls + user ISA == PVM to

execute multiple, concurrent processes

• Each process is given the illusion of

having the entire machine to itself

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PVM: Emulators

• Execute binaries compiled for one ISA on

a machine with a different ISA

• Emulation methods
• Interpretation
• Fast startup, but slow steady-state
• Dynamic binary translation
• High startup overhead, faster steady-state
• Uses a code cache to store translated blocks
• Examples: Java, IA32-EL

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PVM: Binary Optimizers

• Same source and target ISAs
• Main task is optimization
• ABI level optimization
• May also collect performance profiles
• May also enhance security
• e.g., HP's Dynamo

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PVM: High-Level Language VMs

• Designed for VM execution
• Aim to minimize HW- and OS-specific features

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HLL Program Intermediate Code Memory Image Object Code (ISA) Compiler front-end Compiler back-end Loader HLL Program Portable Code ( Virtual ISA ) Host Instructions

• Virt. Mem. Image

Compiler VM loader VM Interpreter/Translator Traditional HLL VM

PVM: High-Level Language VMs

• Distribution format is binary class files
• Virtualized ISA (no real implementation)
• OS interaction via API
• Examples: Java, Micosoft CLI

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Sparc Workstation Java Binary Classes x86 PC Apple Mac VM implementation VM implementation VM implementation

Java VM Architecture

System Virtual Machines

• Supports an OS with many user-level processes
• Couple at the ISA level
• Examples: VMWare, Transmeta Crusoe

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Hardware "Machine" OS Applications Virtualizing Software

Virtual Machine

OS Applications

Guest VMM Host

Classic System Virtual Machine

• Original meaning of the term virtual machine
• All guest and host software use the same ISA
• VMM runs on bare hardware (privileged mode)
• VMM intercepts all privileged operations for the guest OS's

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Linux process Win process HOST PLATFORM

virtual network communication

Guest OS (Windows) Win process Win process Guest OS2 (Linux)

VMM

Linux process Linux process

Hosted VM

• VMM built on top of existing OS
• Advantages
• Installs just like a user-level application
• Host OS provides driver support
• Drawbacks
• Less efficient

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Whole System VMs

• Host and guest do not use a common ISA
• Both app and OS code require emulation
• Typically implemented as a hosted VMM
• Example: VirtualPC

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Co-designed Virtual Machines

• Designed to enable innovative ISA's and/or

hardware implementations

• As if the VM software is part of the HW
• Applications / OS never directly execute native

ISA instructions

• Useful for backwards compatibility
• Example: Transmeta Crusoe

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VM Taxonomy

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