University of Palestine Faculty of Information Technology Multimedia specialist

1. University of Palestine Faculty of Information Technology Multimedia specialist ESGD2204Computer ArchitectureVirtual MachinePrepared By: IbtihalSaiful Islam Makki .ID:120061094Supervised By: Eng. Mohammed TimrazSecond semester

2. PROBLEMS WITH TRADITIONAL COMPUTER SYSTEM • Software compatibility • Limitation by the need to support old interfaces • Optimization across interfaces • Hardware restriction

3. Question • Can a “small” operating system simulate the hardware of some machine so that • Another operating system can run in that simulated hardware? • More than one instance of that operating system run on the same hardware at the same time? • More than one different operating system can share the same hardware at the same time? • Answer: Yes

4. Solution – Virtual Machine • A virtual machine provides interface identical to underlying bare hardware • I.e., all devices, interrupts, memory, page tables, etc. • Virtual Machine Operating System creates illusion of multiple processors • Each capable of executing independently • No sharing, except via network protocols

5. Virtual Machines

6. Virtual machine basics • A virtual machine is a software implementation of a machine (computer) that executes programs like a real machine.

7. Virtual machine applications • Emulation • Emulating one instruction set with another

8. Virtual machine applications • Optimization • Optimizing an existing application binary for the same instruction set

9. Virtual machine applications • Replication • Replicating a virtual machine so that multiple Oses can be supported simultaneously

10. Virtual machine applications • Composing virtual machine software to form a more complex flexible system

11. Virtual machine architecture • Virtualization: A piece of software that provides an interface identical to the underlying bare hardware. - the upper-layer software has the illusion of running directly on hardware - the virtualization software is called virtual machine monitor • Multiplexing: It may provide several virtualized machines on top of a single piece of hardware. - resources of physical computer are shared among the virtual machines - each VM has the illusion of owning a complete machine • Trust and privilege - the VM monitor does not trust VMs - only the VM monitor runs in full privilege • Compared to an operating system VM monitor is a resource manager, but not an extended machine

12. Process and system VM • A process virtual machine is capable of supporting an individual process. • A process virtual machine is created along with its guest process and terminates when the guest process terminates • A system virtual machine provides a complete system enviroment. • This enviroment can support multiple user processes: a file system, I/O devices, GUI…

13. Why Virtual Machine? • Allow flexible management of “machines” at software level 􀂄 experimenting with new architecture 􀂄 debugging an OS 􀂄 checkpointing and migrating all state on a machine • Enhanced reliability and security 􀂄 VM monitor much smaller than OS, therefore: 􀂄 the full privileged code base (VM monitor) is small 􀂄 the trusted code base (VM monitor) is small • Strong isolation between VMs 􀂄 fault and resource isolation

14. Virtualization Approach – Direct Execution • Directly executing VM code to attain high speed • CPU virtualization - VM monitor catches timer interrupts and switches VM if necessary • I/O access virtualization - cause a trap to VM monitor, which processes appropriately • - extra overhead is not too bad • Memory virtualization - a trap at each memory access is not a very good idea

15. Memory Virtualization Under DirectExecution (protected page table) • From the VM OS’s view, the page table • contains mapping from virtual to VM physical addresses • For proper operation, the page table hooked • up with MMU must map virtual to real • machine addresses • VM OS cannot directly access the page table: - each page table write is trapped, for a translation (the physical address field is translated from VM).

16. Memory Virtualization Under DirectExecution (shadow page table) • VM OS maintains virtual to VM physical (V2P) page table • VM monitor - maintains a VM physical to machine (P2M) mapping table . - combines V2P and P2M table into a virtual to machine mapping table. • (V2M) - supplies the V2M table to the MMU hardware • Page table updates - any VM change on its V2P page table must be trapped by VM monitor - VM monitor modifies V2M table appropriately

17. Virtual Machine Transparency • Sometimes you want OS work differently from original: - for correctness: - e.g., non-faulting access to privileged state - for performance: - e.g., batched multiple monitor traps through a single explicit monitor call - e.g., a quick check of whether a monitor call is necessary • Less-than-full transparency (para-virtualization): - modified OS runs within VM - Example: Xen • Full transparency (perfect virtualization): - stock OS (without change) can run within VM - Example: VMware - binary translation for unvirtualizable instructions