COMP25212: Virtualization 3

COMP25212: COMP25212: Virtualization 3Virtualization 3

Subtitle: “What can we do to a VM?”

Learning Objectives:– To understand the VM-handling

mechanisms of a hypervisor

– To understand how many different value-added services are constructed on top of VM-handling mechanisms

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Stopping a VMStopping a VM

Hypervisor stops and starts VM all the time:– to share CPUs– to serialize access to

resources

• Stop by:– Saving CPU registers

into Hypervisor data area

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ApplicationsApplications

Guest AOperating System


Virtual Machine Monitor/HypervisorVirtual Machine Monitor/Hypervisor


Host HardwareHost Hardware

Guest BOperating System


Virtualized

Starting a VMStarting a VM

• Hypervisor:– gains control (e.g.

clock tick)– saves previous VM’s

CPU registers– loads next VM’s

CPU registers– jumps to next VM’s

next-PC (in correct privilege state)

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Virtualized

VM State While VM State While StoppedStopped

VM State:– Memory (all guest

physical memory)• includes Application

state, OS state

– CPU state (registers)– Small amount of I/O

state• Let’s stop VM when

I/O is quiescent!

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Virtualized

““Freeze” a VMFreeze” a VM

• Once suspended, the VM image is self-contained– VM can be (e.g.)

copied to a file(LARGE file!)

• Now, what else can we do with this?

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CPU registersCPU registers

I/O stateI/O state

Move a VMMove a VM

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Host Hardware XHost Hardware X



Virtualized



Guest COperating System


Virtualized

Host Hardware YHost Hardware Y




Snapshot and Rollback Snapshot and Rollback a VMa VM

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Virtualized







…

Think: Optimizations?

Archive a VMArchive a VM

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Rapid ProvisioningRapid Provisioning

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Virtualized




Virtual AppliancesVirtual Appliances

• http://www.vmware.com/appliances/directory/

• over 1000 downloadable appliances

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• e.g.:• mail server• web server• hotel system• virus scanner• firewall

http://www.vmware.com/appliances/directory/

Deploying Secure Deploying Secure DesktopsDesktops

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Virtualized Desktop Machine


Guest Operating System

Guest Operating System

Live MigrationLive Migration

• Optimizing migration from “source” to “destination” VMM:– Repeat:

• Suspend VM on “source” machine• Reset all “dirty” bits in VMM’s page tables• Resume VM on “source” machine• Copy all non-“dirty” pages to destination machine

– Until only minimal subset of pages left– Suspend VM on “source”– Copy remaining pages to “destination”– Resume VM on “destination”

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Load BalancingLoad Balancing

• Management software monitors “load” on all physical machines

• If loads are mismatched, migrate a VM from a loaded to a less-loaded machine

Independent of Application!

Independent of Operating System!

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High AvailabilityHigh Availability

• For critical applications, keep a standby VM available on a different hardware system

• Regularly copy active VM image to standby VM (but don’t activate it)

• Activate standby VM if active VM stops responding (VM crashes? VMM crashes? Hardware system fails?)

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Documents

COMP25212: Virtualization 3