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1.Emulation
• Do whatever the CPU does but in software
• Fetch the next instruction
• Decode – is it an ADD, a XOR, a MOV?
• Execute – using the emulated registers and memory
Example:
addl %ebx, %eax
is emulated as:
enum {EAX=0, EBX=1, ECX=2, EDX=3, …};
unsigned long regs[8];
regs[EAX] += regs[EBX];](https://image.slidesharecdn.com/virtualizationnew-240915024230-ac2b7d6e/85/Operating-system-Virtualization_NEW-pptx-28-320.jpg)
Uploaded bySenthil Vit
Operating system Virtualization_NEW.pptx
The document provides a comprehensive overview of virtualization, defining it as the division of computer resources into multiple execution environments to enhance resource utilization. It explores the history of virtualization, the challenges associated with x86 architecture, various types of virtual machines, and key techniques in CPU and memory virtualization. The document also discusses hypervisors, emphasizing their role in enabling virtual machines to operate on physical hardware, and compares different virtualization technologies and their implications.
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Operating system Virtualization_NEW.pptx
- 1.
- 2. Agenda • Virtualization –Definition • History of Virtualization • Challenges in x86 architecture • Introduction to VMs • CPU virtualization • Memory Virtualization • I/O Virtualization • Types of Hypervisors • Xen • VMware Workstation
- 3. What is Virtualization? “Virtualization is a framework or methodology of dividing the resources of a computer into multiple execution environments, by applying hardware and software partitioning, time-sharing, partial or complete machine simulation and/or emulation” Allows to run multiple OS on a single Physical machine Allows to dynamically create execution environments •Isolation •Encapsulation
- 4. History of Virtualization •In 1960, mainframe computers are used to run a single application at a time and waste a lot of resources. • Split the resources of a mainframe computer and to execute multiple applications. • In 1980, x86 becomes a dominant architecture, introduces master-slave paradigm and virtualization no longer needed.
- 5. Continued … • 1990,massive growth in computer technology and introduces a lot of challenges. – Low hardware infrastructure utilization; – Rising physical infrastructure costs; – Rising IT management costs; – Insufficient disaster protection; and – High maintenance and costly end-user desktops.
- 6. Challenges in virtualizingx86 architecture • Ring Aliasing • Address space compression • Non faulting access to privileged state ( sensitive instructions) • Interrupt virtualization
- 7. Virtualization through Ring Compression VirtualMachine Monitor (VMM) runs at ring 0 Kernel(s) run at ring 1 Requires that CPU is virtualizable 0 VMM 1 2 3 user kernel
- 8. Benefits of Virtualization •Easy manageability • Elimination of Compatibility issues • Fault isolation • Improved security • Improved utilization • Portability • Testing • Rapid deployment • Reduced Costs
- 9.
- 10. Research Activities @ CARE 11 VirtualizationFunctions Sharing Virtual Resources Resources Examples: LPARs, VMs, virtual disks, VLANs Benefits: Resource utilization, workload manageability, flexibility, isolation Aggregation Virtual Resources Resources Examples: Virtual disks, IP routing to clones Benefits: Management simplification, investment protection, scalability Emulation Virtual Resources Resources Examples: Arch. emulators, iSCSI, virtual tape Benefits: Compatibility, investment protection, interoperability, flexibility Insulation Add, Replace, or Change Virtual Resources Resources Examples: Spare CPU subst., CUoD, SAN-VC Benefits: Continuous availability, flexibility, investment protection Resource Type Y Resource Type X
- 11. Introduction to Virtualmachines • The key to managing complexity in computer systems is their division into levels of abstraction separated by well-defined interfaces. • Levels of abstraction allow implementation details at lower levels of a design to be ignored or simplified, thereby simplifying the design of components at higher levels.
- 12.
- 13. Interfaces • Well-defined interfacesallow computer design tasks to be decoupled so that teams of hardware and software designers can work more or less independently. • EX: Hardware engineers focused to implement the IA32 instruction set on hardware, whereas the software engineers developed a compiler that convert HLL to the IA32 instruction set.
- 14. Drawbacks of Interfaces •Subsystems and components designed to specifications for one interface will not work with those designed for another. – e.g., Intel IA-32 and IBM PowerPC • Application programs, when distributed as program binaries, are tied to a specific instruction set and operating system. • An operating system is tied to a computer that implements specific memory system and I/O system interfaces.
- 15. Continued … • Theimplicit assumption is that the hardware resources of a system are managed by a single operating system. This binds all hardware resources into a single entity under a single management regime. • In turn, limits the flexibility of the system, not only in terms of available application software, but also in terms of security and failure isolation, especially when the system is shared by multiple users or groups of users.
- 16.
- 17. Virtualization • Virtualization providesa way of relaxing the foregoing constraints and increasing flexibility. When a system (or subsystem), e.g., a processor, memory, or I/O device, is virtualized, its interface and all resources visible through the interface are mapped onto the interface and resources of a real system actually implementing it.
- 18.
- 19. Common terminologies • UserISA – ISA exposed for user applications • System ISA – ISA exposed for supervisory system • Application Binary Interface – User ISA and System Call • Instruction Set Architecture separates hardware from rest • Application Binary Interface separates processes from rest
- 20.
- 21. Types of Virtualmachines • Process Virtual Machine • System Virtual Machine
- 22. Process Virtual Machines Virtualizingsoftware translates a set of OS and user-level instructions composing one platform to another, forming a process virtual machine capable of executing programs developed for a different OS and a different ISA.
- 23. Continued … • Supportingindividual processes • Virtualization software is placed over the ABI • Host – underlying platform • Guest – software in VM • Native – platform in the VM • Virtualizing software – runtime that supports the guess process and runs on top of operating system.
- 24. System VM • Providesa complete system environment. • Supports an operating system along with its potentially many user processes. • Provides a guest operating system with access to underlying hardware resources, including networking, I/O, a display and graphical user interface.
- 25.
- 27. CPU virtualization – SoftwareTechniques
- 28. 29 1.Emulation • Do whateverthe CPU does but in software • Fetch the next instruction • Decode – is it an ADD, a XOR, a MOV? • Execute – using the emulated registers and memory Example: addl %ebx, %eax is emulated as: enum {EAX=0, EBX=1, ECX=2, EDX=3, …}; unsigned long regs[8]; regs[EAX] += regs[EBX];
- 29. 30 Continued … • Pro: –Simple! • Con: – Slooooooooow • Example hypervisor: BOCHS
- 30. 31 2. Trap andemulation • Run the VM directly on the CPU – no emulation! • Most of the code can execute just fine – E.g., addl %ebx, %eax • Some code needs hypervisor intervention – int $0x80 – movl something, %cr3 – I/O • Trap and emulate it! – E.g., if guest runs int $0x80, trap it and execute guest’s interrupt 0x80 handler
- 31. 32 Continued … • Pro: –Performance! • Cons: – Harder to implement – Need hardware support • Not all “sensitive” instructions cause a trap when executed in user mode • E.g., POPF, that may be used to clear IF • This instruction does not trap, but value of IF does not change! – This hardware support is called VMX (Intel) or SVM (AMD) – Exists in modern CPUs • Example hypervisor: KVM
- 32. 33 3. Dynamic (binary)translation • Take a block of binary VM code that is about to be executed • Translate it on the fly to “safe” code (like JIT – just in time compilation) • Execute the new “safe” code directly on the CPU • Translation rules? – Most code translates identically (e.g., movl %eax, %ebx translates to itself) – “Sensitive” operations are translated into hypercalls • Hypercall – call into the hypervisor to ask for service • Implemented as trapping instructions (unlike POPF) • Similar to syscall – call into the OS to request service
- 33. 34 Continued … • Pros: –No hardware support required – Performance – better than emulation • Cons: – Performance – worse than trap and emulate – Hard to implement – hypervisor needs on-the-fly x86-to-x86 binary compiler • Example hypervisors: VMware, QEMU
- 34. 35 4.Paravirtualization! • Does notrun unmodified guest OSes • Requires guest OS to “know” it is running on top of a hypervisor • E.g., instead of doing cli to turn off interrupts, guest OS should do hypercall(DISABLE_INTERRUPTS)
- 35. 36 Continued … • Pros: –No hardware support required – Performance – better than emulation • Con: – Requires specifically modified guest – Same guest OS cannot run in the VM and bare-metal • Example hypervisor: Xen
- 36. Hardware Technique -VTx • Two new VT-x operating modes – Less-privileged mode (VMX non-root) for guest OSes – More-privileged mode (VMX root) for VMM • Two new transitions – VM entry to non-root operation – VM exit to root operation Ring 3 Ring 0 VMX Root Virtual Machines (VMs) Apps OS VM Monitor (VMM) Apps OS VM Exit VM Entry Execution controls determine when exits occur Access to privilege state, occurrence of exceptions, etc. Flexibility provided to minimize unwanted exits VM Control Structure (VMCS) controls VT-x operation Also holds guest and host state
- 38.
- 39.
- 40. 1. Shadow PageTables
- 42.
- 43.
- 44. Continued … • ExtendedPage Table • A new page-table structure, under the control of the VMM – Defines mapping between guest- and host-physical addresses – EPT base pointer (new VMCS field) points to the EPT page tables – EPT (optionally) activated on VM entry, deactivated on VM exit • Guest has full control over its own IA-32 page tables – No VM exits due to guest page faults, INVLPG, or CR3 changes Guest IA-32 Page Tables Guest Linear Address Guest Physical Address Extended Page Tables Host Physical Address EPT Base Pointer (EPTP) CR3
- 45. Guest Linear Address EPT Tables CR3 EPT Tables + EPTTables + Page Table Page Directory Host Physical Address Guest Physical Page Base Address + Guest Physical Address Continued … • All guest-physical memory addresses go through EPT tables – (CR3, PDE, PTE, etc.) • Above example is for 2-level table for 32-bit address space – Translation possible for other page-table formats (e.g., PAE)
- 46.
- 47. Continued … Pro: HigherPerformance Pro: I/O Device Sharing Pro: VM Migration Con: Larger Hypervisor Hypervisor Shared Devices I/O Services Device Drivers VM0 Guest OS and Apps VMn Guest OS and Apps Monolithic Model Pro: Highest Performance Pro: Smaller Hypervisor Pro: Device assisted sharing Con: Migration Challenges Assigned Devices Hypervisor VM0 Guest OS and Apps Device Drivers VMn Guest OS and Apps Device Drivers Pass-through Model VT-d Goal: Support all Models Pro: High Security Pro: I/O Device Sharing Pro: VM Migration Con: Lower Performance Shared Devices I/O Services Hypervisor Device Drivers Service VMs VMn VM0 Guest OS and Apps Guest VMs Service VM Model
- 52. Packet Receive inVirtualized I/O
- 53. Packet Receive inPass through I/O
- 54. High level viewof Virtualization
- 55.
- 56. Host Machine Physical Hardware AvailableResources Limitations Capacity Planning Managing Complexity Is it nuts and bolts? May I know my usage? Can I exceed ? How can I decide? Multiple VMs?
- 57. Virtualization Software PR Access Creation Management Schedule MCInterface Hosting How a VM Communicate ? Is it support creation? Is it support single VM mgmt? Is it support Multiple VM mgmt? Can I visualize ? Over OS or Hardware?
- 58. Virtual Machine &Guest OS Virtual hardware and Virtual BIOS Guest OS Is it OS + hardware? Is guest OS aware?
- 59. 60 Two types ofhypervisors • Definitions – Hypervisor (or VMM – Virtual Machine Monitor) is a software layer that allows several virtual machines to run on a physical machine – The physical OS and hardware are called the Host – The virtual machine OS and applications are called the Guest VMware ESX, Microsoft Hyper-V, Xen Hardware Hypervisor VM1 VM2 Type 1 (bare-metal) Host Guest Hardware OS Process Hypervisor VM1 VM2 Type 2 (hosted) VMware Workstation, Microsoft Virtual PC, Sun VirtualBox, QEMU, KVM Host Guest
- 60. Guest OperatingSystem The operating system that Xen hosts Domain The virtual machine under which a guest operating system executes Example Guest OS = Program domain = Process Hypervisor A particular Xen version which handles low level functionality Bare-metal Hypervisor - Xen
- 62. Hosted VMware Architecture VMwareachieves both near-native execution speed and broad device support by transparently switching* between Host Mode and VMM Mode. Guest OS Applications Guest Operating System Host OS Apps Host OS PC Hardware Disks Memory CPU NIC VMware App Virtual Machine VMware Driver Virtual Machine Monitor Host Mode VMM Mode VMware, acting as an application, uses the host to access other devices such as the hard disk, floppy, or network card The VMware Virtual machine monitor allows each guest OS to directly access the processor (direct execution) *VMware typically switches modes 1000 times per second
- 63. Networking in VMwareworkstation
- 64. VMware vs. Xen •VMware can run any x86 OS unmodified • Xen provides better performance (usually 2% on benchmark tests vs. 20%) • Xen doesn’t support Windows yet since it is illegal to modify Windows • Xen takes more work to get it up and running • Xen is free and is being supported by the Linux community including Red Hat (Fedora)
- 65.