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System Virtualization 1

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Title: System Virtualization 1 Author: Alasdair Rawsthorne Last modified by: alasdair Created Date: 3/8/2010 9:37:30 AM Document presentation format – PowerPoint PPT presentation

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Title: System Virtualization 1


1
System Virtualization 1
  • Learning Objective
  • To understand the implementation choices and
    details of System Virtualization

2
Aims and Definitions
Application
Applications
Applications
Guest A Operating System
Guest B Operating System
Operating System
Hardware
Virtual Machine Monitor/Hypervisor
Host Hardware
Unvirtualized
Virtualized
Host Guest
3
Hosted Virtualization
Applications
Applications
Application
Guest A Operating System
Guest B Operating System
Virtual Machine Monitor/Hypervisor
Host Operating System
Host Hardware
Advantages? Disadvantages?
4
Xen Guest 0 Virtualization
Applications
Applications
Application
Guest 0 Operating System
Guest B Operating System
Guest A Operating System
Virtual Machine Monitor/Hypervisor
Host Hardware
Advantages? Disadvantages?
5
Protection/Privilege
  • OS handles physical resources
  • Privileged
  • Application isolated from resources
  • Non-privileged

Application
Operating System
Hardware
Unvirtualized
6
Protection/Privilege
  • VMM handles physical resources
  • Privileged
  • Guest OS isolated from resources
  • non- (less-)privileged

Applications
Applications
Guest A Operating System
Guest B Operating System
Virtual Machine Monitor/Hypervisor
Host Hardware
Virtualized
VMM gets control on every guest OS access to
physical resource
7
What Physical Resources are Guarded?
  • Timers
  • CPU registers
  • Interrupt Enable
  • Page Table Base
  • Device Control Registers
  • Programmed I/O?
  • Interrupt I/O?
  • DMA I/O?
  • Interrupts (may be for different Guest?)
  • Memory Mapping (page tables)

8
How does Guest Cause VMM Entry?
  • VMM designers are (a bit) lucky
  • Many Guest accesses to physical resources cause
    trap in non-privileged mode
  • So, running the OS in non-privileged mode
    suffices
  • BUT some instructions behave differently (without
    trapping) in privileged and non-priv mode
  • e.g. Intel Store into Flags

9
Memory Accessing in Virtualization
OS Page Tables ( TLBs for efficiency)
Virtual Address
Physical Address
Unvirtualized
VMMPage Tables
OS Page Tables
Virtual Address
Virtual Address
TLBs ??
Virtualized
10
Interfacing Guest OS and VMM
  • Three solutions today
  • Software (static)
  • Software (dynamic)
  • Hardware (dynamic)

11
ParaVirtualization
  • Modify Guest OS to be Virtualization-aware
  • call VMM for all privileged operations
  • cooperate with VMM over shared page tables
  • call VMM for input-output
  • Advantages? Disadvantages?

12
Detect and Fix Interfaces in VMM
  • Detection
  • Write-protect Guest OS page tables
  • Code-scan (Dynamic Binary Translation?) Guest OS
    for unsafe instructions plant traps
  • Fixing
  • Use write-error trap to detect guest page-table
    writes
  • Provide shadow page tables for hardware TLBs
  • Use illegal instruction and trap traps

13
Detect and Fix Interfaces in Hardware
  • Requirement
  • VMM runs more-privileged than Guest OS
  • Hardware provides Application/OS and VMM modes
  • When Virtualization is active, all OS accesses to
    physical resources trap to VMM
  • Advantages? Disadvantages?

14
The Manchester Solution
  • watch this space
  • or help make it happen!
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