virtualization

red: solutions

faster

hardware changes _ than software

portability

ease of _ and migration

isolation

_ of failing or attacked components

simulating

main principle of virtualization is _ hardware or software in a virtual environment

instruction set architecture

set of machine instructions

privileged instructions

allowed to be executed only by the operating system, can only be executed in user mode

general instructions

can be executed by any program

system calls

offered by an operating system

library calls

also known as application programming interface

process vm

platform-independent, seperate set of instructions, and interpreter/emulator running atop an os

native vmm

has direct access to hardware, low-level instructions, along with bare bones minimal OS instructions

hosted vmm

runs on top of existing os, may be slower due to extra os layer

trap to the OS

switch control from user to kernel mode for the OS to perform a privileged operation on behalf of the user program

control-sensitive instruction

may affect the configuration of a machine, may trap (e.g., one affecting relocation register or interrupt table).

behavior-sensitive instruction

effect is partially determined by the system context (e.g., POPF sets an interrupt-enabled flag, but only in system mode).

subset

For any conventional computer, a virtual machine monitor may be constructed if the set of sensitive instructions for that computer is a _ of the set of privileged instructions.

executed

Problem: the condition is not always satisfied

There may be sensitive instructions that are _ in user mode without causing a trap to the operating system.

emulate

_ all instructions

wrap

_ nonprivileged sensitive instructions to divert control to VMM

paravirtualization

modify guest OS, either by preventing nonprivileged sensitive instructions, or making them nonsensitive (i.e., changing the context).; guest OS uses hypercalls for privileged operations.

infrastructure as a service

covering the basic infrastructure; be sharing a physical machine with other customers ⇒ almost complete isolation between customers

platform as a service

covering system-level services

software as a service

containing actual applications