Virtual Machines: Concepts & Applications
Mohamed Zahran (aka Z) mzahran@cs.nyu.edu http://www.mzahran.com
CSCI-GA.3033-015
Lecture 1: So … What Is A Virtual Machine?
Disclaimer: Many slides of this lecture
are based on the slides of authors of the textbook from Elsevier.
All copyrights reserved.
Who Am I?
• Mohamed Zahran (aka Z)
• http://www.mzahran.com
• Research interest:
– computer architecture
– hardware/software interaction – Biologically-inspired machines
• Office hours: Tue 1-3 pm
– or by appointment
• Room: WWH 320
Formal Goals of The Course
• Understand VM architectures and applications
• Study key implementation technologies
• Focus on architecture and
microarchitecture aspects; as well as software aspects
• Cover significant case studies
Informal Goals of This Course
• Be an expert in how programming
languages, compilers, OS, and computer architecture interact together!
• Be able to use the technology learned in this course in many different situations
• Build a vision about technology and its future
• Enjoy the course
The Textbook
Grades
• You have 3 sources of study information:
– Slides
– Notes you take in class
– Reading material from the textbook
• Exam is open book/notes
• Grade distribution:
– Homework assignments 30%
– Project 30%
– Final exam 40%
We Have to Admit that …
• Computers are very complicated structures!
• In order to manage/design them, we need to be able to manage extreme complexity!
• The best way to do that is through:
levels of abstraction with well defined interfaces
Abstraction
• Computer systems are built on levels of abstraction
Higher level of abstraction hide details at lower levels
Example: files are an abstraction of a disk
file file
abstraction
I/O devices and Networking Controllers
System Interconnect (bus)
Controllers Memory Translation Execution Hardware
Drivers Memory
Manager Scheduler Operating System
Libraries Application
Programs
Main Memory
Software
Hardware
Abstraction provides:
Simplified interface to underlying resources.
High Level Language
Assembly Language
Machine Language
Microarchitecture
Logic Level
Problem Algorithm Development Programmer
Compiler (translator)
Assembler (translator)
Control Unit (Interpreter)
Microsequencer (Interpreter)
Device Level Semiconductors Quantum
Advantages of Well-defined Interfaces
• Major design tasks are decoupled
• Different hardware and software development schedules
• Example of interfaces:
– Instruction set architecture (ISA) – OS interface (system calls)
• Software can run on any machine supporting a compatible interface
PowerPC or x86 MacOS
MacIntosh apps.
x86 Linux
Linuxapps
x86 Windows
Windowsapps.
12
Major Program Interfaces
• ISA Interface -- supports all conventional software
System Calls
User ISA System ISA
ISA
Application Software Operating System
System Calls
User ISA System ISA
ABI
Application Software Operating System
Application Binary Interface (ABI)
-- supports application software only
There are also disadvantages…
• Software compiled for one ISA will not run on hardware with a different ISA
– Apple Mac (PowerPC) binaries on an x86?
• Even if ISAs are the same, OSes may differ
– Windows NT applications on a Solaris x86?
• Binary may not be optimized for the specific hardware platform it runs on
– Intel Pentium 4 binaries on an AMD Athlon?
MacOS
MacIntosh apps
ARM x86
Windows apps.
Linux
Disadvantages (contd.)
• Innovation may be inhibited by fixed ISA
– Hard to add new instructions
• OR remove obsolete ones
– What was the most recent (successful) new ISA?
Or new OS?
• Difficult for software to interact directly with implementation
– Performance features – Power management – Fault tolerance
– Software is supposed to be implementation independent
Diversity in instruction sets,
OSes, and programming languages
Encourages innovations Discourages stagnation
In practice, diversity leads to reduced interoperability.
BUT
How to deal with this in our world of networked computers, where it is advantageous To move software as freely as data??
A Look at Hardware Resources
• Conventional system software manages hardware resources directly
– An OS manages the physical memory of a specific size
– I/O devices are managed as physical entities
• Difficult to share resources except through OS – All users of hardware must use the same OS
– All users are vulnerable to attack from other users sharing the resource (via security holes in OS)
Can we do better?
Virtualization is the answer!
• Real system is transformed so that it appears to be different!
• An isomorphism from guest to host
– Map guest state to host state – Implement “equivalent” functions
S i S
S i ' S j '
Guest
Host
V( S i ) V( S j ) e (S i )
e '(S i ')
j
Virtualization
• Similar to abstraction
Except
– Details not necessarily hidden
• Construct Virtual Disks
– As files on a larger disk – Map state
– Implement functions
file file
virtualization
abstraction
The “Machine”
• Different perspectives on what the Machine is:
– OS developer
– Compiler developer
– Application programmer
I/O devices and Networking
System Interconnect (bus)
Memory Translation Execution Hardware
Application Programs
Main Memory Operating System
Libraries
Hardware
"Machine"
OS
Applications
Virtualizing Software
Virtual Machine
OS
Applications
Guest
VMM
Host
Virtual Machines
add Virtualizing Software to a Host platform
and support Guest process or system on a Virtual Machine (VM) Example: System Virtual Machine
Example of VM Usages
• A virtualizing software installed on an Apple Macintosh can provide a
Windows/IA-32 VM capable of running PC application programs.
• Multiple, replicated VMs can be implemented on a single hardware
platform to provide groups/individuals with their own OS environments
Example of VM Usages
• A large multiprocessor server can be divided into smaller virtual servers.
• VM can provide dynamic, on-the-fly optimization of program binaries.
• …
The Family of Virtual Machines
• Lots of things are called “virtual machines”
IBM VM/370 Java
VMware
Some things not called “virtual machines”, are virtual machines
IA-32 EL Dynamo
Transmeta Crusoe
Virtual Machines
Process Virtual Machines System Virtual Machines
The process of virtualization involves two steps:
1. Mapping of virtual resources or state to real resources of the underlying machine.
2. Using real machine instructions and/or system calls
to carry out the actions specified by the VM instructions.
Process VMs
• Execute application binaries with an ISA different from hardware platform
• Provide user application with a virtual ABI environment
• Can provide: replication, emulation, and optimization
• Examples: IA-32 EL, FX!32
Virtualizing Software Application Process
Machine OS
Hardware
Guest Runtime
Host
Application Process
Virtual Machine
Process Virtual Machines
• Constructed at ABI level
• Runtime manages guest process
• Not persistent
• Guest processes may intermingle with host processes
• As a practical matter, guest and host OSes are often the same
• Dynamic optimizers are a special case
• Examples: IA-32 EL, FX!32, Dynamo
HOST OS
Disk
file sharing
network communication guest
process
create host process
guest process
runtime runtime
guest process
runtime
host process
Example of Process VM:
FX!32
Application compiled for source ISA (in this example IA-32)
Executed on a machine with target ISA (in this example Dec Alpha)
Process VM: Replication
• OS providing the illusion of multiprogramming
• Each user process thinks it has the complete machine to itself
Process VM: Emulation
• Supports program binaries compiled for a different instruction set than the
host hardware emulates one
instruction set on hardware designed for another instruction set
• Interpretation Vs Translation
Process VM: Optimization
Same-ISA Dynamic Binary Optimizers
• Optimize Binary at Runtime
• Instruction sets for host and guest are the same
• Example HP Dynamo
– Can optimize for dynamic properties of program
– Can optimize for a specific
processor implementation HP PA
UNIX
HP Apps
Process VM:
High Level Language Virtual Machines
• VM environment does not directly correspond to any real platform
• VM environment designed for:
– ease of portability
– to match features of HLL used for program development.
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
HLL VM: Example JVM
Sparc Workstation
Java Binary Classes
x86 PC
Apple Mac VM
implementation
VM implementation
VM implementation
Java VM Architecture
System Virtual Machines
• Provide a complete system environment
• Constructed at ISA level
• Persistent
• Examples: IBM
VM/360, VMware, Transmeta Crusoe
guest process
HOST PLATFORM Guest OS
VMM guest
process
guest process
guest process Guest OS2
VMM guest
process guest process
A single host hardware platform can support multiple guest OS environments simultaneously.
System Virtual Machines
• Native VM System
–VMM privileged mode –Guest OS user mode –Example: classic IBM
VMs
• User-mode Hosted VM
–VMM runs as user application
• Dual-mode Hosted VM
–Parts of VMM
privileged;
parts non-privileged –Example VMware
Non-privileged modes
Privileged Mode Virtual
Machine
VMM
Hardware Virtual Machine
Host OS
Hardware VMM Virtual Machine
Host OS
Hardware VMM
Examples
Examples
Co-Designed VMs
Different objective:
Enable innovative ISA and/or hardware implementation for improved performance and/or power.
Co-Designed VMs
VLIW Windows
X86 Apps
Perform both translation and optimization
VM provides interface between standard ISA software and implementation ISA
Transmeta Crusoe and IBM Daisy best- known examples
Composition: Example
Java application
Linux x86
JVM
Windows x86
VMware
Crusoe VLIW
Binary Translation
A computer user has a Java application running on laptop PC
The user has Linux installed on Windows PC via Vmware.
The IA-32 hardware is in fact a Transmeta Crusoe implementing VLIW ISA.
Taxonomy
Multiprogrammed Systems
Java VM MS CLI
Transmeta Crusoe
same ISA different
ISA
Process VMs System VMs
Virtual PC for Mac different
ISA same ISA
IBM VM/370
VMware HP
Dynamo
IA-32 EL FX!32
Conclusions
• Virtualization will be a key part of future computer systems.
• A fourth major discipline? (with HW, System SW, Application SW)
• VMs have been investigated and built by OS developers, language designers,
compiler developers, and hardware designers!
• In this course, we will study the underlying concepts and technologies that are
common across the whole spectrum.
