Virtualization Technology

Virtualization Technology

Prof. Dan Connors

2Copyright © 2006, Intel Corporation. All rights reserved. Prices and availability subject to change without notice.*Other brands and names are the property of their respective owners

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Virtualization

Real vs. Virtual

• Similar essence, effect

• ”Formally” different

A framework that combines or divides [computing] resources to present a transparent view of one or more environments

• Hardware/software partitioning (or aggregation)

• Partial or complete machine simulation

• Emulation (partial or complete)

• Time-sharing (in fact, sharing in general)

• In general, can be M-to-N mapping (M “real” resources, N “virtual” resources)

• Examples: VM (M-N), Grid Computing (M-1) , Multitasking (1-N)


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Virtualization: Motivation Areas

Server consolidation

Application Consolidation

Sandboxing

Multiple execution environments

Virtual hardware

Debugging

Software migration (Mobility)

Appliance (software)

Testing/Quality Assurance


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Types of Virtualization

Process & application virtualization

• Process executes on CPU with modification of native instructions

• Created binary instrumentation and translation systems

CPU/Machine virtualization

• Each process feels like it has its own CPU

• Created by OS preemption and scheduler

Memory virtualization

• Process feels like it has its own address space

• Created by MMU, configured by OS

Storage virtualization (Input/Output)

• Logical view of disks “connected” to a machine

• External pool of storage


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Application Level Virtualization

Java Virtual Machine (JVM)

• Executes Java byte code (virtual instructions)

• Provides the implementation for the instruction set interpreter (or JIT compiler)

• Provides code verification, SEH, garbage collection

• Hardware access through underlying OS

JVM Architecture

• Stack-based architecture

• No MMU

• Virtual hardware: PC, register-set, heap, method (code) areas

• Rich instruction set– Direct object manipulation, type conversion, exception throws

Provides a runtime environment through JRE

Other Examples: .NET CLI, Parrot (PERL 6)


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CPU Virtualization


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Virtual CPUs

Each process feels like it has its own CPU

• But cannot execute privileged instructions (e.g., modify the MMU or the interval timer, halt the processor, access I/O)

Created by OS preemption and scheduler

Pseudo-machine with interpreted instructions

• 1966: O-code for BCPL

• 1973: P-code for Pascal

• 1995: Java Virtual Machine

Run anywhere


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Virtual Machines

Machine virtualization

• Partition a physical computer to act like several real machines

• Migrate an entire OS + applications from one machine to another

Early examples

• 1972: IBM System 370


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HARDWARE

KERNEL

USER LEVEL LIBRARIES

APPLICATIONS

API Calls

System Calls

Instructions

User Space

Kernel Space

Machines: Stacked Architecture


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Possible Virtual Abstraction Levels

Instruction Set Architecture

• Emulate the ISA in software– Interprets, translates to host ISA (if required)– Device abstractions implemented in software– Inefficient

• Optimizations: Caching? Code reorganization?

• Applications: Debugging, Teaching, multiple OS

Hardware Abstraction Layer (HAL)

• Between “real machine” and “emulator” (maps to real hardware)

• Handling non-virtualizable architectures (scan, insert code?)

• Applications: Fast and usable, virtual hardware (in above too), consolidation, migration


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Possible Abstraction Levels

Operating System Level

• Virtualized SysCall Interface (may be same)

• May or may not provide all the device abstractions

• Easy to manipulate (create, configure, destroy)

Library (user-level API) Level

• Presents a different subsystem API to application

• Complex implementation, if kernel API is limited

• User-level device drivers

Application (Programming Language) Level

• Virtual architecture (ISA, registers, memory, …)

• Platform-independence ( highly portable)

• Less control on the system (extremely high-level)


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Machine Virtualization

Privileged vs. unprivileged instructions

Regular applications use unprivileged instructions

• Easy to virtualize

If regular applications execute privileged instructions, they trap

• VM catches the trap and emulates the instruction


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Virtual Machine Monitor (VMM)

Hypervisor- Program in charge of virtualization

• Arbitrates access to physical resources

• Presents a set of virtual device interfaces to each host

Guest OS runs until:

• Privileged instruction traps

• System interrupts

• Exceptions (page faults)

• Explicit call: VMCALL (Intel) or VMMCALL (AMD)


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Approaches

Intel x86 arch doesn’t support trapping privileged instructions

Two approaches to modifying OS to run on virtual machine:

• Binary translation (BT)– Scan instruction stream and replace instructions – Replace privileged instructions with something the VM can intercept. (VMWare approach)

• Paravirtualization– Don’t use non-virtualizable instructions (Xen approach)

– Static design approach, paravirtualization support is designed before dynamic adaptation


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Binary Translation and Binary Instrumentation


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Translation Approaches

•Source instrumentation:– Instrument source programs

•Binary instrumentation:– Instrument executables directly

Advantages for binary instrumentation

Language independent Machine-level view

Instrument legacy/proprietary software


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When to instrument:

• Instrument statically

• Instrument dynamically

Advantages for dynamic instrumentation

No need to recompile or relink

Discover code at runtime

Handle dynamically-generated code

Attach to running processes

Instrumentation Approaches


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www.pintool.org - Support for Binary Translation

Easy-to-use Instrumentation:

• Uses dynamic instrumentation – Do not need source code, recompilation, post-linking

Programmable Instrumentation:• Provides rich APIs to write in C/C++ your own instrumentation tools (called Pintools)

Multiplatform:• Supports x86, x86-64, Itanium, Xscale• Supports Linux, Windows, MacOS

Robust:

• Instruments real-life applications: Database, web browsers, …

• Instruments multithreaded applications

• Supports signals

Efficient:• Applies compiler optimizations on instrumentation code


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Pin (VM) Software Architecture of Binary Translation

JIT Compiler

Emulation Unit

Virtual Machine (VM)

Code

Cache

Instrumentation APIs

Ap

pli

cati

on

Operating SystemHardware

PinPintool

Address space


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BT: Instrumentation Approaches

JIT Mode

• Pin creates a modified copy of the application on-the-fly

• Original code never executes

More flexible, more common approach

Probe Mode

• Pin modifies the original application instructions

• Inserts jumps to instrumentation code (trampolines)

Lower overhead (less flexible) approach


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JIT-Mode Instrumentation

Original codeCode cache

Pin fetches trace starting block 1 and start instrumentation

7’

2’

1’

Pin

2 3

1

7

45

6

Exits point back to Pin


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Pin transfers control intocode cache (block 1)

2 3

1

7

45

67’

2’

1’

Pin


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7’

2’

1’

PinPin fetches and instrument a new trace

6’

5’

3’trace linking

2 3

1

7

45

6


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Original Code

A

B C

D

FE

A’

C’

F’

D’

Code Cache

Hot Path,Found withHardware

E

D

B

A

C

Original Code

F

JIT Code Model


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Transformation cost: Start-up (initialization) overhead

A black line represents a service request from the virtual machine. Space between adjacent black lines indicates time being spent in already compiled code paths.

time

Significant demands on the run-time system

Light-weight application


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Persistence

A B C D C Original dynamic instruction streamA

1) A’ B’ C’ D’ C’ A’JIT JIT JIT JIT



2) A’ B’ C’ D’ C’ A’

Traditional JIT

Persistent JIT


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Instrumentation Approaches

JIT Mode

• Pin creates a modified copy of the application on-the-fly

• Original code never executes

More flexible, more common approach

Probe Mode

• Pin modifies the original application instructions

• Inserts jumps to instrumentation code (trampolines)

Lower overhead (less flexible) approach


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A Sample Probe

•A probe is a jump instruction that overwrites original instruction(s) in the application– Instrumentation invoked with probes– Pin copies/translates original bytes so probed

functions can be called

Entry point overwritten with probe:

0x400113d4: jmp 0x41481064

0x400113d9: push %ebxCopy of entry point with original bytes:

0x50000004: push %ebp0x50000005: mov %esp,%ebp0x50000007: push %edi0x50000008: push %esi0x50000009: jmp 0x400113d9

Original function entry point:0x400113d4: push %ebp0x400113d5: mov %esp,%ebp0x400113d7: push %edi0x400113d8: push %esi0x400113d9: push %ebx


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Popular VM Platforms

Xen

• Runs under an OS and provides virtual containers for running other operating systems. Runs a subset of x86. Routes all hardware accesses to the host OS.

Altris Software Virtualization Services

• Windows registry & directory tweaking

• Allows multiple instances of applications to be installed

Microsoft Virtual Server

Parallels

VMWare


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Overall Picture

ISA HAL OS Library PL

Performance * **** **** *** **

Flexibility **** *** ** ** **

Development &

Implementation

** * *** ** **

Degree of

Isolation

*** **** ** ** ***

(More stars are better)


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Instruction Set Architecture Level Virtualization

Technologies

• Emulation: Translates guest ISA to native ISA

• Emulates hardware specific IN/OUT instructions to mimic a device

• Translation Cache: Optimizes emulation by making use of similar recent instructions

• Code rearrangement

• Speculative scheduling (alias hardware)

Issues

• Efficient Exception handling

• Self-modifying code


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ISA Level Virtualization: Examples

Bochs: Open source x86 emulator

• Emulates whole PC environment– x86 processor and most of the hardware (VGA, disk, keyboard,

mouse, …)– Custom BIOS, emulation of power-up, reboot– Host ISAs: x86, PowerPC, Alpha, Sun, and MIPS

Crusoe (Transmeta)

• “Code morphing engine” – dynamic x86 emulator on VLIW processor

• 16 MB “translation cache”

• Shadow registers: Enables easy exception handling

QEMU:

• Full Implementation– Multiple target ISAs: x86, ARM, PowerPC, Sparc– Supports self-modifying code– Full-software and simulated (using mmap()) MMU

• User-space only: Useful for Cross-compilation and cross-debugging


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HAL Virtualization Techniques

Standalone vs. Hosted

• Drivers

• Host and VMM worlds

• I/O

Protection Rings

• Multilevel privilege domains

Handling “silent” fails

• Scan code and insert/replace artificial traps

• Cache results to optimize


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VMware Architecture


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Paravirtualization

Traditional architectures do not scale

• Interrupt handling

• Memory management

• World switching

Virtualized architecture interface

• Much simpler architectural interface

• Virtual I/O and CPU instructions, registers, …

Portability is lost


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Examples

Denali

• Simpler customized OS with no VM for network applications

Xen

• Simpler port to commercial OS

• Exposes some “real” hardware, e.g. clock, physical memory address

Virtualization Technology

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