Module 14: Virtualization

Question 1

virtualization

Answer 1

the ability for a computer to run multiple OSes on the same physical machine

Question 2

host

Answer 2

the underlying physical machine hardware

Question 3

virtual machine manager / hypervisor

Answer 3

software that allows creating and running virtual machines on the host machine; the VM’s each then run with their own operating systems and applications; the VMM manages the computing, memory, and storage resources required for the VMs

Question 4

guest OS

Answer 4

user-level process that usually runs an OS system over the VMM hypervisor

Question 5

host OS

Answer 5

the OS that runs on the hardware (for a type 2 hypervisor)

Question 6

type 0 hypervisor

Answer 6

a hypervisor that’s implemented in firmware or hardware; hardware is statically partitioned across different guest OSes

Question 7

type 1 hypervisor

Answer 7

the hypervisor itself essentially replaces the OS and runs in kernel mode; the guest OS believes it is running on bare metal

Question 8

type 2 hypervisor

Answer 8

the VMM hypervisor runs on top of the host OS in user mode as a process; the host doesn’t know that the VMM is running guest OSes

Question 9

sandboxing

Answer 9

a type of virtualization in which a tightly controlled environment with a guest OS and isolated set of resources is created to allow untested, unverified, or untrusted programs to run; this technique helps maintain security for the host machine or host OS

Question 10

VM templating

Answer 10

create an OS system and application image, and clone it across multiple VMs saving installation the effort of doing manual software installations

Question 11

virtual cpu (VCPU)

Answer 11

a software emulation of a CPU that represents the state of the CPU (including the PCB and execution state) for each of the guest OSes)

Question 12

trap and emulate

Answer 12

when the guest OS of the VM attempts to execute a privileged instruction, since it is in user mode, the action will cause a “trap”; the VMM will handle the trap and execute the instruction attempted by the guest, then return control to the guest in user mode

Question 13

binary translation

Answer 13

an alternative to trap and emulate in which instead of doing trap-and-emulate for every instruction that runs in the guest OS, the guest OS instructions are translated to equivalent instructions in the VMM. the original assembly code from the guest OS is simply translated to the code for the equivalent implementation in the VMM

Question 14

CPU scheduling for virtualization

Answer 14

given multiple VCPUs and physical CPUs, the scheduling algorithm decides which VCPU to run next on a given CPU

Question 15

memory management for virtualization

Answer 15

guest page table: maps the guest OSes virtual addresses to what the guest OS believes to be the physical addresses

host page table: the guest physical addresses are separately mapped to host virtual addresses

shadow page table: maintained by the VMM to map guest virtual addresses to host physical addresses, optimizing the translation process to manage virtualization; the shadow page table is loaded into the MMU during a context switch

Question 16

full virtualization

Answer 16

the guest OS is unaware of the hypervisor and believes it is running on bare metal

Question 17

paravirtualization

Answer 17

the guest OS is aware of the underlying hypervisor and thus implements optimizations given this knowledge; the shadow page table and efficient I/O techniques are examples of paravirtualization

Question 18

efficient I/O in paravirtualization

Answer 18

a circular buffer maintains all the intermediate I/O state between the guest and the VMM through shared memory which results in much better performance than dealing with the levels of indirection between the guest OS and physical device

Question 19

application containment

Answer 19

containerization is an alternative to full virtualization that allows isolating individual applications; the different containers run on the host OS and have standard formats; the container virtualization layer allows the containers to communicate and abstracts the specific host OS from the application containers

Question 20

microservices

Answer 20

complication applications are broken down into modular components called microservice; each service has its own process

Question 21

programming environment virtualization

Answer 21

a custom environment designed for a programming language that includes features that enable optimized execution (e.g. Java Virtual Machine)