Lecture 2

Question 1

What are the 3 fundamential Abstractions?

Answer 1

• Interipreters/Processors
• Memory
• Communication Links

(Hard to manage resources)

Resources Management:

• High peak demands -> OVERPRVISIONING
• HETROGENTITY for h/w + s/w
• Machine Failure

Question 2

What is virtualisation?

Answer 2

• Virtualisation is a ‘virutal’ creation of something
• It ABSTRACTS the resources and SIMPLIFIES it; it ISOLATES users from one another + SUPPORTS REPLICATION to increase elasticity

Question 3

How does virtualisation stimulate a physical object?

Answer 3

• Reduces IT costs but increases utilisation, flexibility + effiency on exisiting hardware.
• Runs multiple OS & Applications on the SAME server at the SAME TIME to increase utilisation + flexibility of hardaware

Important:

• Performance Isolation: Assigns + accounts resources to different applications.
• System security: Isolates services + runs on the same hardware.
• Performance & Reliability: allows appliations to mitigate from one platform to another.

Question 4

What is Layering and the importance

Answer 4

a common approach to manage SYSTEM COMPLEXITY

Important

• It simplifies subsystems, abstract via interfaces with other subsystems
• Minimises interaction SUBSYSTEMS of a COMPLEX SYSTEMS
• Can DESIGN, IMPLEMENT + MODIFY individually and independently

Question 5

Interfaces

Answer 5

• ISA - Provides commands to the processor
• Application Binary Interface (ABI) - an INTERFACE between two program modules‘library/OS’ at machine code to access HARDWARE - invokes system calls
• Appreciation Program Interface (API) - A set of routine/tools to build software applications (Gives access to the ISA; HLL library calls to invoke system calls
• A dynamic binary translation: Converts BLOCKS of guest instructions from PORTABLE CODE to the host instruction to improve performance.
  
  • Blocks are CACHED + REUSED

Question 6

Difference between VMM & VM

Answer 6

• Partitions resources into separate virtual machines
• Allows SEVERAL OS to run concurrently on a platform
• VM is an execution environment, runs on OS, it is an isolated environment but has access to PORTIONS of the computer resources

Question 7

VMM advantages

Answer 7

Allows:

• Multiple SERVICES to share the SAME platform
• Live mitigation: Movement of a server from one platform to another
• System Modification - Maintaining BACKWARD compatiability of the original system

Question 8

How does the VMM virtualises the CPU + Memory?

Answer 8

1. Traps PRIVILEDGED INSTRUCTIONS execute by a guest OS + enforces the safety operation.
2. Traps INTERRUPTS + dispatches them to individual guest
3. Controls VIRTUAL MEMORY MANAGEMENT
4. Maintains SHADOW PAGE TABLE for guest OS replicates made by guest OS (Uses MMU for translation)
5. Monitor SYSTEMS PERFORMANCE to take action to avoid performance degration.

Question 9

What is guest OS?

Answer 9

A guest OS runs VM under VMM

Question 10

Name and Describe the Hypervisions

Answer 10

1. Type 1 - (Native) VM runs directly from the hardware
2. Type 2 - (Hosted) User mode - VM runs on the OS

Question 11

Dual-Mode Operation + Difference between Kernal and User Mode

Answer 11

allows OS to protect itself + the system components

Kernal mode = “INTERRUPT HANDLERS”:

• Has access to the hardware
• Can execute CPU instruction + reference memory access
• Reserved for lowest levels of the OS
• When the computer crashes, the PC halts

User mode runs EVERYTHING:

• Has NO access to the hardware or reference memory
• Code running on use mode must delegate system API’s to access hardware + memory
• Crashes in a system in user mode is recoverable

Question 12

Challanges in x86 Virtualisation

Answer 12

• There are 4 layers of priviledge execution rings.
• The “Host computer system hardware” must exectute the priviledge ring 0 first.
• It requires a layer on top under the OS to deliver and manage shared resources

Question 13

What are the 3 classes of machine instructions?

Answer 13

• Priviledge instructions - Executed in kernal mode, when executed, it causes a TRAP and executes in kernal mode.
• Non-priviledged instructions - the ones that can be executed in user mode.
• Sensetive instructions - can be executed in EITHER user/kernal mode but BEHAVE differently. (Requires special precautions at execution time)

Question 14

What are the 3 techniques of Virtualisation CPU on x86?

Answer 14

• Full Vertualisation using Binary Translation
• Paravirtualisation
• Hardware assisted Virtualisation

Question 15

Technique 1: Full Virtualisation using Binary Translation

Answer 15

• Uses a set of binary translation + direct execution
• Guest OS runs unchanged under VMM if directly from the hardware platform
• Runs exact copy of the actual copy
• Binary: REWRITES parts of the code to REPLACE sensitive but not priviledge instruction with safe code to emulate orginal instruction
• Advantages: No hardware assistance, No change to guest OS, Isolation + Security
• Disadvantages: Speed of execution

Examples: VMware, Micosoft Virtual Server

Question 16

Technique 2: Paravirtualisation

Answer 16

• Greek: “With” the guest OS and hypervisior to improve performance + efficency.
• Modifies the kernal OS to replace Non virtualisation layer hypervisor
• Provides hypercall for other critical kernal operations

(Provides: Memory management, interrupt handling and time keeping.)

Advantages: Faster execution, lower virutalisation

Disadvantags: Compatability and Portability is poor.

Examples: Xen & Denali

Question 17

Technique 3: Hardware assited virtualisation

Answer 17

• New CPU execution mode that allows the VMM to run NEW ROOT below 0.
• Advantages: FASTER execution
• Examples: Intel VT-x, Xen 3.x

Question 18

Linux Containers

Answer 18

• is a Linux Process (or Processes) that a virtual environment with its own process network space
• Containers share portions of the kernal