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Virtualization
Dr. Michael L. Collardwww.sdml.info/collard
www.sdml.info/collard/[email protected]
1
Platform Virtualization• Hide the physical characteristics of computer
resources from the applications• Not a new idea: IBM’s CP-40 1967, CP/CMS, VM• Full Virtualization
• Simulate enough hardware so that an unmodified guest operating system can be run
• Provides a full “virtual machine”• Scenarios:
• Run Linux in a virtual machine on Windows• Run multiple logical servers (each with their own
virtual machine) on a single physical server
Virtual Machine Monitors (VMMs)Virtual Machine Monitors (VMMs)
...
Virtual Machine Monitor (VMM)
VMnVM0 VM1
Platform HW
I/O DevicesProcessor/CSMemory
AppnApp0
Guest OS0
App1
Guest OS1 Guest OSn
Source: Understanding Intel Virtualization Technology”, N. Sahgal, D. Rodgers
Platform Hardware
VM1
VM Monitor
VM0
Guest OS0
App AppApp ...
... Guest OS1
App AppApp ...
OS and Apps in a VM don't know that the
VMM exists or that they share CPU resources
with other VMs
VMM should run protected from all
Guest software
Challenges of Running a VMMChallenges of Running a VMM
VMM should isolate Guest SW stacks from
one another
VMM should present a virtual platform
interface to Guest SW
Source: Understanding Intel Virtualization Technology”, N. Sahgal, D. Rodgers
Popek & Goldberg
• Formal Requirements for Virtualizable Third Generation Architectures – 1974 article
• Virtual Machine• capable of virtualizing all hardware resources,
processors, memory, storage, and peripherals
• Virtual Machine Monitor (VMM)• provides virtual machine abstraction• Also referred to as hypervisor
Popek & Goldberg VMM Properties
• Equivalence• Program running under a VMM should exhibit a
behavior identical to that of running on the equivalent machine
• Resource Control• VMM is in full control of virtualized resources
• Efficiency• A statistically dominant fraction of machine
instructions may be executed without VMM intervention
Popek & Goldberg: Instructions
• Privileged instructions• those that trap in user mode, and only run in
system mode• Control-sensitive instructions
• those that change the resource configuration of the system
• Behavior-sensitive instructions• behavior or results depend on the configuration of
resources
Theorem 1: Virtualization
• Can construct a VMM if set of control-sensitive instructions is a subset of the privileged instructions• All control-sensitive instructions always trap and
pass control to the VMM• Guarantees resource control property• non-privileged instructions must be executed
natively
Theorem 2: Recursive Virtualization
• Recursive virtualization – VMM can run on a copy of itself
• For an architecture, this is possible if:• The architecture is virtualizable• A VMM without timing dependences can be built
Non-Virtualizable Machines
• VMMs (under Popek & Goldberg definition) cannot be build on non-virtualizable machines
• Workarounds:• patching – critical instructions removed and
replaced with trap to VMM• paravirtualization – guest o.s. is modified (e.g.,
IBM VM)
x86 Virtualization
• Before 2005:• x86 processor architecture did not meet Popek &
Goldberg virtualization requirements
• Intel VT (Virtual Technology) (IVT)• IA-32, IA-64, Directed I/O, DMA & interrupt
remapping, Connectivity
• AMD-V (Pacifica)• AMD Athlon 64, Turion, Opteron
Virtualization: IsolationVirtualization: Isolation
HW
App2App1
OS
VMM
HW
App1 App2
OS OS
Source: Understanding Intel Virtualization Technology”, N. Sahgal, D. Rodgers
Virtualization: ConsolidationVirtualization: Consolidation
HW1 HW2
App2App1
OS1 OS2
VMM
HW
App2App1
OS1 OS2
Source: Understanding Intel Virtualization Technology”, N. Sahgal, D. Rodgers
Virtualization: MigrationVirtualization: Migration
VMM
HW1
App
HW2
VMM
OS
VMM
HW1
App
HW2
VMM
OS
Source: Understanding Intel Virtualization Technology”, N. Sahgal, D. Rodgers
Usages
• Legacy software support – Consolidation• Training/QA – Consolidation• Activity Partioning – Isolation• Administration – Consolidation, Isolation,
Migration• Failover Infrastructure - Migration
Questions about a VMM
• What OS does it run on? Does it need an OS?• What OSs does it allows as guests?• Can it support a VM even if the instructions
are not on the physical CPU, e.g., IA-64 VM on IA-32 machine?
• How much can the resources be shared between guest Oss?
• What tools does it provide for managing VMs?
VMWare
• Desktop – runs in a host OS– VMWare Workstation (1999) – runs on PC– VMWare Fusion – runs on Mac OS X– VMWare Player – run, but not create images
• Server– VMWare Server (GSX Server) –hosted on Linux or
Windows– VMWare ESX (ESX Server) – no host OS– VMWare ESXi (ESX 3i) – freeware (July 2008)
VMWare ESX
• Part of VMWare Infrastructure• Runs “bare-metal”, i.e., has its own vmkernel,
with near native performance• Guest/Host CPU: x86 (ESXi only), x86-64, AMD• Guest OS: Windows, Linux• Management capabilities:
– Move VM between servers on the fly– Move VM based on host/VM load
requirements/demands
Microsoft Hyper-V
• Viridian, Windows Server Virtualization• Host CPU: x64 + IVT or AMD-V• VMM runs directly on the hardware, however
requires one parent partition of Windows Server 2008. Parent manages child VMs
• Guest OS: Windows, SUSE, Linux (?)• Enlightened I/O: direct access for enabled
guests
Other
• Xen– free software– runs native, but with required “dom0” OS (Linux,
NetBSD, Solaris), which starts other VMs
• UML (User Mode Linux)– free software– Run Linux in Linux– Support integrated into Linux kernel
Summary
• Virtualization is an old approach, but new software techniques and hardware support have it becoming more visible
• New tools/method/processes being developed to fully utilize virtualization
• In the mainstream of system administration
