benefit of virtualiza/on? Virtualiza/on An interpreter may not work! Requirements for Virtualiza/on 1/06/15 Which of the following is not a poten/al

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1 1/06/15 Benefits of virtualiza/on Virtualiza/on Which of the following is not a poten/al benefit of virtualiza/on? A. cost effec/ve B. applica/on migra/on is easy C. improve applica/on performance D. run legacy applica/ons E. support flexible sojware development F. support the opera/on of the Cloud 2 Requirements for Virtualiza/on An interpreter may not work! Hypervisors should score well in three dimensions: Safe to use but the performance sucks. 1. Safety: hypervisor should have full control of virtualized resources. 2. Fidelity: behavior of a program on a virtual machine should be iden/cal to same program running on bare hardware. 3. Efficiency: much of code in virtual machine should run without interven/on by hypervisor. In order to sa/sfy the performance criterion, most of the code should be executed directly. 3 Not easy, e.g. Intel x86 architecture Binary transla/on may be performed to mi/gate the hardware limita/on. 4 1

2 Quick discussion Should we re- write all sensi/ve instruc/ons? What s your argument? The difference between true virtualiza/on and paravirtualiza/on True virtualiza/on and paravirtualiza/on 5 Which are true about paravirtualiza/on? A. Paravirtualiza/on may make the guest system run faster. B. The guest system believes it has full control and direct access to the hardware. C. Paravirtualiza/on supports only process- level virtualiza/on. D. Paravirtualiza/on is a rela/vely new technology. Type 1 and Type 2 Hypervisors (1) Loca/on of type 1 and type 2 hypervisors. 7 2

3 Example hypervisors Trap- and- Emulate technology Examples of the various combina/ons of virtualiza/on type and hypervisor. Type 1 hypervisors always run on the bare metal whereas type 2 hypervisors use the services of an exis/ng host opera/ng system. When the opera/ng system in a virtual machine executes a kernel only instruc/on, it traps to the hypervisor if virtualiza/on technology is present. Virtualizing the Unvirtualizable Support for sensi/ve instruc/ons The basic technology is binary transla/on Do you s/ll remember basic block from NWEN242? The binary translates rewrites the guest opera/ng system running in ring 1, while the hypervisor runs in ring 0 What should we do when transla/ng a basic block? 12 3

4 Quick exercise Why dynamic code transla/on can be fast in prac/ce? An implementa/on preference Will hardware with VT support perform befer than the hardware without VT? A. Translated code can be cached. B. Computer hardware provides features that support fast transla/on. C. Transla/on is not needed for many basic blocks in the kernel. D. Transla/on is not needed for basic blocks in user programs. 13 Some/mes sojware beats hardware! Moreover, translated code can be faster than the original code. 14 Virtual machine interface An example of VMI Linux Memory virtualiza/on Virtualiza/on complicates memory management. Virtual machine 1 requires virtual pages 7, 4, and 3 to be mapped to physical frames 10, 11, and 12. Virtual machine 2 requires virtual pages 4, 5, and 6 to be mapped to physical frames 10, 11, and 12. What should the hypervisor do? A. Reject the request from virtual machine 2 B. Accept the request but map virtual pages to different physical frames. 16 4

5 Building the shallow page table How to keep shallow page table updated? Hardware Support For Nested Page Tables Guest virtual address, guest physical address, host physical address Solu/on 1: keep track of the page containing the page table. Solu/on 2: update page table in the event of a page fault. 17 Extended/nested page tables are walked every /me a guest physical address is accessed including the accesses for each level of the guest s page tables. Reclaiming memory Over- commitment of memory, why? A. Improve u/liza/on of hardware B. Enhance applica/on performance. C. Enable efficient resource sharing. D. Simplify management of physical resources. Virtual memory ballooning A technique for the hypervisor to reclaim memory back from the virtual machine How can we reclaim memory?

6 Clouds Na/onal Ins/tute of Standards and Technology defines characteris/cs of cloud 1. On- demand self- service 2. Broad network access 3. Resource pooling 4. Rapid elas/city 5. Measured service Quick exercise Which of the following isn't an advantage of cloud? A. No worries about running out of storage B. Highly reliable access to compu/ng resources C. Easy access to informa/on D. Paying only for what you use Quick exercise What is the name of the organiza/on helping to foster security standards for cloud compu/ng? A. Cloud Security Standards Working B. Cloud Security Alliance C. Cloud Security WatchDog D. Security in the Cloud Alliance 23 6