OutlineMainCharacteristicsofCloudComputingWhyVirtualization?HardwareVirtualizationFullvirtualizationParavirtualiztionHardware-assistedvirtualizationDeviceDriverVirtualizationMemoryVirtualizationLocalvs.Distributed2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-1MainCharacteristicsofCloudComputingOn-demandself-serviceBroadnetworkaccessResourcepoolingRapidelasticityMeasuredservice2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-2MainCharacteristicsofCloudComputingOn-demandself-serviceSystemdemandsresourceautomaticallyBroadnetworkaccessResourcepoolingVirtualizingresourcessuchasmemory,storage,CPUintopools.RapidelasticityProvisioningorreleasingresourcesatanytimeMeasuredservice2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-3HistoryofVirtualization(1)1964–IBMCP-40.1965–IBMSystem/360-67,withvirtualmemoryhardware.1999–FullVirtualization.VMware.2003–Para-Virtualization.Xen.2005–HW-AssistedVirtualization.IntelVT-x,AMD-V.2006–QEMU.2007–KVM(Kernel-basedVirtualMachine).Linux2.6.20.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-4HistoryofVirtualization(2)Fromanotherperspective,thedevelopmentofvirtualizationcanbedividedintothefollowingstages:MainframeVirtualizationDesktopVirtualizationServerVirtualizationCloudComputingNowadays.MobileVirtualizationOntheway.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-5HistoryofVirtualization(3)Thereasonsofx86virtualization:Lowinfrastructureutilization.Increasingphysicalinfrastructurecosts.IncreasingITmanagementcosts.Insufficientfailoveranddisasterprotection.Highmaintenanceend-userdesktop.x86iswidespread.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-6ApplyingVirtualizationtoCloudWithvirtualizingresources,theycaneasilybeputintopools.VirtualizedCPUandmemoriescanbedistributeddynamicallytovirtualmachinesinrealtime.LeadstoRapidelasticityandOn-demandself-serviceImagine‘hotplugmemories/CPU’intomachines.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-7HardwareVirtualization(1)Howtorealizex86virtualization?What’stheproblemencountered?Howtodealwiththeproblem?2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-8HardwareVirtualization(2)Howtorealizex86virtualization?What’stheproblemencountered?Howtodealwiththeproblem?2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-9HardwareVirtualization(2)2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueTraditionally,OSisatRing0forhardwareresourcemanagement.Whenrealizingvirtualization,VMMisatRing0,andOSisdowngradedtoRing1.U01-10HardwareVirtualization(2)AccordingtoPopekandGoldberg,CPUinstructionscanbeclassifiedintothreesets.Privilegedinstructions.Sensitiveinstructions.Criticalinstructions.*1:GJPopekandRPGoldberg,“Formalrequirementsforvirtualizablethirdgenerationarchitectures”,CommunicationoftheACM,vol17,pp.412-421,July,1974.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-11HardwareVirtualization(3)Howtorealizex86virtualization?What’stheproblemencountered?Howtodealwiththeproblem?2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-12HardwareVirtualization(3)InstructionwhichwillmodifytheconfigurationofresourcesshouldeitherbeexecutedinRing0(privilegedmode)ortrap.Thereare17instructionsinx86architecturemaycauseproblem.Why?Theyareunprivileged.Won’tcausetrapwhenexecution.Theyexposephysicalprocessorstate.Revealsomedetailswhichshouldn’tbe.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-13HardwareVirtualization(4)Howtorealizex86virtualization?What’stheproblemencountered?Howtodealwiththeproblem?2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-14HardwareVirtualization(4)Therearethreeapproachesforvirtualizationavailablenowadays.FullVirtualization.ParaVirtualization.Hardware-AssistedVirtualization.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-15FullVirtualizationBinaryTranslation.Replacenonvirtualizableinstructionswithnewsequencesofinstructionswhichhavethesameeffectasoriginalonthevirtualhardware.Manyinstructionsreplaceone,soiftheinstructionisfrequentlyused,theoverheadishuge.Hugecostonresources.Bettercompatibility.VMware,QEMU.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-16ParaVirtualization(1)AlsonamedOS-assistedvirtualization.OSkerneladaptation.Performingcorrespondinghypercallsinsteadoftheoriginalprivilegedinstructions.LowcostofCPUandI/O.CompatibilityworsethanFullVirtualization.Meetproblemswhenthekernelisnotopen.CitrixXenserver,Microsofthyper-V.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-17ParaVirtualization(2)Hypercallisquitesimilartosystemcall.ImplementationofXen.Systemcall:aninterrupt(0x80)fromuserspacetokernelspace.Hypercall:aninterrupt(0x82)fromguestdomain(Ring1)tohypervisor(Ring0).Bothsystemcalltableandhypercalltablearedefinedinfile“arch/x86/kernel/entry_64.S”.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-18Hardware-AssistedVirtualization(1)Re-designthehardwarearchitecture.Addnewinstructionsetsforx86architecturetotrapthosenonvirtualizableinstructions.Conceptually,hypervisorstaysat“Ring-1”.Noneedtode-privilegetheguestOS.AMDAMD-V,IntelVT-x.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-19Hardware-AssistedVirtualization(2)IntelVT-x:FirstsupportedbyPentium4(Model662and672)on2005.Twooperatingmode:VMXRootOperation(forVMM).Non-RootOperation(forGuestOS).ExtentedPageTables.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-20Hardware-AssistedVirtualization(3)AMDAMD-V:On2006,firstsupportedbyAthlon64,Athlon64X2andAthlon64FX.Twomodesforhypervisortohandlememorypartitioning:ShadowPageTables.NestedPageTables.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-21DeviceDriverVirtualization–theIdeaVirtualmachinesneedtheirowndevicedrivers.ForguestOSstocommunicatewithphysicalhardware.Mostvirtualizationsolutionsemulatedsimpledevicesthatthedriversalreadyexisted.LikeIDEinterfaceandNE2000(averyoldnic).2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-22DeviceDriverVirtualization–inPracticeXenHypervisor’sparavirtulizationsolution:Requestsfromfront-enddriversinDomUwritesintoaring-buffersharedwithDom0.Dom0handlestherequestbytheback-enddriversinkernel,andaccessthehardwarebyrealdrivers.Thenback-endwriteresponsebackandconsumedbyguest.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-23DeviceDriverVirtualizationTheSplitDriver2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-24MemoryVirtualizationModernOperatingsystemandx86hardwaremostlysupportmemoryvirtualization.Inuser-spaceapplicationsaccesstovirtualmemorywithpagingmechanism.VMinstancehostswithaOSsupportvirtualmemorymeansanadditionlayersofmemorymapping.NewerCPUshaveoptimizationsforadditionlayersofmapping.AdditionalTaggedTLBsincasethatwhenswitchingVMstheTLBwillbeflushed.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-25MemoryVirtualization–inPracticeInfullvirtualization,hypervisortrapseveryactiontrytoupdatepagetable.Atoncehypervisortrapstheaction,hypervisorcantakeover.InXenparavirtualization,para-virtualizedOSdirectlyinvokehypercallstoaskhypervisorupdatethepagetable.Muchfaster.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-26DistributedMemoryVirtualization–theIdeaPoolingthevirtualizedmemoryWecanaddnodesintoourcloudtoextendthememorycapacity.BreakingtheboundofphysicalmachinesIfanVMinstanceinanodeneedmorememories,itcangetmemoriesfromothernodes.2023/7/23CloudOperatingSystem-Uint09:CoreTechniqueU01-27DistributedMemoryVirtualization–inPracticePerformanceissue.Relativelyveryveryhighlatencycomparetolocalmemories.LatencyofInfinibandor10GEthernet:1.07~2.6μs.LatencyofDDR3SDRAM:10.5ns.Pagetablefordistributedenvironmentaddsevenmoreoverhead.Therefore,mainstreamhypervisorsdon’tsupportdistributedmemoryvirtualization,fornow.2023/