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Virtualization Dr. Michael L. Collard 1.

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1 Virtualization Dr. Michael L. Collard 1

2 Platform Virtualization Hide the physical characteristics of computer resources from the applications Not a new idea: IBMs CP , 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

3 Virtual Machine Monitors (VMMs)... Virtual Machine Monitor (VMM) VM n VM 0 VM 1 Platform HW I/O DevicesProcessor/CSMemory App n App 0 Guest OS 0 App 1 Guest OS 1 Guest OS n Source: Understanding Intel Virtualization Technology, N. Sahgal, D. Rodgers

4 Platform Hardware VM 1 VM Monitor VM 0 Guest OS 0 App... Guest OS 1 App... 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 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

5 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

6 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

7 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

8 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

9 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

10 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)

11 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

12 Virtualization: Isolation HW App 2 App 1 OS VMM HW App 1 App 2 OS Source: Understanding Intel Virtualization Technology, N. Sahgal, D. Rodgers

13 Virtualization: Consolidation HW 1 HW 2 App 2 App 1 OS 1 OS 2 VMM HW App 2 App 1 OS 1 OS 2 Source: Understanding Intel Virtualization Technology, N. Sahgal, D. Rodgers

14 Virtualization: Migration VMM HW 1 App HW 2 VMM OS VMM HW 1 App HW 2 VMM OS Source: Understanding Intel Virtualization Technology, N. Sahgal, D. Rodgers

15 Usages Legacy software support – Consolidation Training/QA – Consolidation Activity Partioning – Isolation Administration – Consolidation, Isolation, Migration Failover Infrastructure - Migration

16 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?

17 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)

18 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

19 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 Parent manages child VMs Guest OS: Windows, SUSE, Linux (?) Enlightened I/O: direct access for enabled guests

20 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

21 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

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