Virtual Machines (part 2)

1. Virtual Machines (part 2) CPS210 Spring 2006

2. Papers • Xen and the Art of Virtualization • Paul Barham • ReVirt: Enabling Intrusion Analysis through Virtual Machine Logging and Replay • George Dunlap

3. X Virtualization in the enterprise • Consolidate under-utilized servers to reduce CapEx and OpEx X • Avoid downtime with VM Relocation • Dynamically re-balance workload to guarantee application SLAs X • Enforce security policy

4. VMware architecture Host World VMM World Target App Target App Host App VM App Target OS Host OS Virtual Machine Monitor VM Driver Host Machine

5. SimOS architecture Target App Target App Target OS SimOS Host App Host App Host OS Host Machine

6. SimOS memory SimOS SimOS VMemory SimOS code, data Target OS TargOS code, data Target App TargApp code, data Target App Virtual MMU SimDisk Host OS SimDisk File Mem File Host Machine

7. SimOS page fault SimOS SimOS Fault handler SimOS VMemory TargOS Fault handler Target OS Unmapped addr Target App Target App Virtual MMU SimDisk Host OS SimDisk File Mem File Host Machine

8. Generic TLB • Cache of recently used PTEs • Small – usually about 64 entries • Huge impact on performance TLB Physical Address or TLB Miss or Access fault Virtual Address

9. x86_32 Address space 4GB S Xen Kernel S 3GB ring 0 ring 1 ring 3 User U 0GB

10. VMware Guest Page Tables Virtual → Machine Update PTE Guest OS Shadow page table VMM Hardware MMU

11. Para-Virtualizing the MMU • Guest OSes allocate and manage own PTs • “Hypercall” to change PT base • Xen must validate PT updates before use • Validation rules applied to each PTE: 1. Guest may only map phys. pages it owns 2. PT pages may only be mapped RO

12. Xen guest page tables Virtual → Machine Update PTE Guest OS 1) Validation check 2) Perform update VMM Hardware MMU