1 / 11

Virtualization

Virtualization. Reference . Formal Requirements for Virtualizable Third Generation Architectures, Gerald Popek and Robert Goldberg, CACM, V17 N7, July 1974 http://portal.acm.org/citation.cfm?id=361011.361073. Advantages. Resource configuration (RAM, devices, etc)

umika
Download Presentation

Virtualization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Virtualization

  2. Reference • Formal Requirements for Virtualizable Third Generation Architectures, Gerald Popek and Robert Goldberg, CACM, V17 N7, July 1974 http://portal.acm.org/citation.cfm?id=361011.361073

  3. Advantages • Resource configuration (RAM, devices, etc) • Run multiple (different) O/S’s concurrently • Test new releases • Isolation • Scalability (multiprocessor systems)

  4. Modes of Operation • Full simulation (NOT a true VMM) • i.e.; instructions do not run natively • Hybrid VM • I/O resources are programmed by device drivers that run in a deprivilegedservice OS • VMM (often called a hypervisor) • large % of inst’s run natively • All privileged instructions trap to VMM for emulation

  5. Types • Full Virt. • Guest unchanged • Generic device drivers • Paravirtualization • Guest can access host h/w • Modified drivers • H/W assisted • VMM moved to h/w • Requires virtualization h/w

  6. VMM Management • Allocator - resource management • Dispatcher - determines post-trap action • Simulator • performs the instruction • limits effects to the VM • VM sees only its own machine

  7. “Sensitive” i86 Instructions(in protected mode) • Control – can change amount of resources without causing a trap • Behavior – execution depends on real-memory location or mode • Includes: • IN - Input • OUTS - Output String • INS - Input String • CLI - Clear Interrupt-Enable Flag (IF) • OUT - Output STI - Set IF

  8. Privileged i86 Instructions • include: • CLTS - Clear Task-Switched Flag • LMSW - Load Machine Status • HLT - Halt Processor • LTR - Load Task Register • LGDT - Load GDT Register • MOV CRn - Move Control Register • LIDT - Load IDT Register • MOV DRn - Move Debug Register • LLDT - Load LDT Register • MOV TRn - Move Test Register

  9. V86 mode sensitive Inst’s • include: • CLI - Clear IF • POPF - Pop Flags • STI - Set IF • INT n - Software Interrupt • PUSHF - Push Flags • IRET - Interrupt Return • POPF is both IOPL and CPL sensitive. IOPL will only be changed by POPF when executed at CPL = 0. The interrupt flag (IF) will only be changed by POPF if executed with CPL <= IOPL. If POPF does not change IOPL or the interrupt flag due to lack of privilege, no exception is generated.

  10. VMM Types • Type I runs directly on real hardware. • Type II • runs as an application on a host OS • relies on the host OS for • memory management, • processor scheduling, resource allocation, and • hardware drivers. • When a VM traps by attempt to execute a sensitive instruction, the host OS must direct the signal to the VMM • Hybrid • interprets every privileged instruction

  11. X86 Problems • There are Sensitive, Unprivileged instructions • Do not cause an interrupt or exception! • Do not perform intended actions • Guest does not know they “failed”

More Related