Introduction to Virtual Machines. Michael Jantz

Transcription

1 Introduction to Virtual Machines Michael Jantz

2 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 2

3 Introduction to Virtual Machines Abstraction and interfaces Virtualization Computer system architecture Process virtual machines System virtual machines 3

4 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

5 Interfaces Define the communication b/w two entities Hierarchical relationship Linear relationship Software can run on any machine supporting a compatible interface MacIntosh apps. Windows apps. Linux apps MacOS Windows Linux PowerPC x86 x86 5

6 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 6

7 Interfaces: Disadvantages Limit flexibility Developers must work within the constraints of the interface Can be confining ARM binaries on x86 machine? Windows applications on Linux? MacIntosh apps Windows apps. MacOS Linux x86 x86 7

8 Interfaces: Disadvantages Inhibits innovation Hard to change instruction sets Application software cannot directly exploit microprocessor features Software is supposed to be architecture independent! 8

9 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 9

10 Virtualization Creates an isomorphism that maps a virtual guest to a real host e(s i ) S i Guest S j V(S i ) V(S j ) e'(s i ') S i ' Host S j ' 10

11 Virtualization vs. Abstraction Virtualization does not necessarily hide details virtualization file file 11

12 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 12

13 Benefits of VM's Flexibility Portability Isolation Security 13

14 Computer Architecture Architecture: functionality and appearance of a computer system Implementation: embodiment of the architecture 14

15 Computer Architecture Computer systems consist of: Layers of abstraction Well-defined interfaces Application Programs Libraries Operating System Execution Hardware System Interconnect (bus) Memory Translation I/O devices and Networking Main Memory 15

16 The ISA Interface Interface between hardware & software Two parts System ISA User ISA Application Programs Libraries Operating System Execution Hardware System Interconnect (bus) Memory Translation I/O devices and Networking Main Memory 16

17 The ISA Interface System ISA Important for OS developers Application Programs Libraries Operating System Execution Hardware System Interconnect (bus) Memory Translation I/O devices and Networking Main Memory 17

18 The ABI Interface Application Binary Interface (ABI) User ISA + system calls Important for compiler writers Application Programs Libraries Operating System Execution Hardware System Interconnect (bus) Memory Translation I/O devices and Networking Main Memory 18

19 The API Interface Application Programming Interface (API) User ISA + library calls Important for application programmers Application Programs Libraries Operating System Execution Hardware System Interconnect (bus) Memory Translation I/O devices and Networking Main Memory 19

20 Major Program Interfaces ISA supports all conventional software System Calls Application Software Operating System System ISA User ISA ISA ABI supports application software only Application Software System Calls Operating System System ISA User ISA ABI 20

21 Process Virtual Machines Supports an individual process Run SW for a different OS and different ISA Couple at ABI level via runtime system Guest Application Process Application Process Runtime Host OS Machine Virtualizing Software Virtual Machine Hardware 21

22 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) guest process runtime host process create file sharing HOST OS Disk guest process runtime guest process runtime host process network communication 22

23 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 23

24 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 24

25 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 25

26 PVM: High-Level Language VMs Designed for VM execution Aim to minimize HW- and OS-specific features HLL Program HLL Program Intermediate Code Object Code (ISA) Memory Image Compiler front-end Compiler back-end Loader Portable Code ( Virtual ISA ) Virt. Mem. Image Host Instructions Compiler VM loader VM Interpreter/Translator Traditional HLL VM 26

27 PVM: High-Level Language VMs Distribution format is binary class files Virtualized ISA (no real implementation) OS interaction via API Examples: Java, Micosoft CLI Java Binary Classes Java VM Architecture VM implementation VM implementation VM implementation Sparc Workstation x86 PC Apple Mac 27

28 System Virtual Machines Supports an OS with many user-level processes Couple at the ISA level Examples: VMWare, Transmeta Crusoe Guest Applications OS OS Applications VMM Host Virtualizing Software Hardware "Machine" Virtual Machine 28

29 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 Win process Win process Win process Linux process Linux process Linux process Guest OS (Windows) Guest OS2 (Linux) VMM HOST PLATFORM virtual network communication 29

30 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 30

31 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 31

32 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 32

33 VM Taxonomy 33