Operating System Support for Virtual Machines Sam King George Dunlap Peter Chen CoVirt Project, University of Michigan

Operating System Support for Virtual Machines Software abstraction of a machine Software backward compatibility Convenient place for new services Strong isolation Sam King Operating System Support for Virtual Machines

Virtual Machine Configurations Type I VMM Hardware Virtual Machine Monitor Guest Operating System Guest Process Guest Process Guest Process Guest Operating System Virtual Machine Monitor Host Operating System Hardware Type II VMM Runs directly on hardware Good performance Uses existing host OS abstractions to implement services Poor performance Sam King Operating System Support for Virtual Machines

Can we have Type I performance with Type II elegance? Yes! Only 510 lines of code added to Linux Type II VMM attain performance that approaches type I VMM Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Presentation Outline Background on UMLinux Discussion of optimizations Conclusions Sam King Operating System Support for Virtual Machines

UMLinux Architecture Linux on top of Linux Port of Linux to run in UMLinux ptrace used for virtualization intercept guest system calls track guest user / kernel mode transitions Guest Process UMLinux VMM Guest OS Linux Operating System PC Hardware Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Hardware Equivalents Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Performance Sam King Operating System Support for Virtual Machines

Original UMLinux Guest System Call Guest application VMM Process Guest operating system Host operating system Sam King Operating System Support for Virtual Machines

Move VMM to Host Kernel Guest application VMM Process Guest operating system VMM Process Host operating system Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Performance Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Switching Guest Modes Significant number of guest kernel / user mode crossings Kernel compile benchmark: 22 million guest memory exceptions 1.4 million guest system calls Protection provided using mprotect system calls Instead, use x86 segmentation hardware Sam King Operating System Support for Virtual Machines

Use Segmentation Bounds for Kernel Protection Guest OS 0x70000000 Guest Apps 0x00000000 guest kernel-mode segment bound Host OS 0xffffffff 0xc0000000 Accessible Memory Guest OS 0x70000000 Guest Apps 0x00000000 guest user-mode segment bound Host OS 0xffffffff 0xc0000000 Accessible Memory Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Performance Sam King Operating System Support for Virtual Machines

Original UMLinux Guest Application Context Switching RAM File RAM File Guest Application Memory Guest Application Memory proc_a mem proc_a mem 0x8000 0x8000 proc_b mem proc_b mem process_a running process_b page at 0x8000 mapped in, process_b executes Sam King Operating System Support for Virtual Machines

Multiple Address Space Definitions Instead, modify hardware page table pointer guest proc a guest proc b Guest OS switchguest syscall Page Table Ptr Host operating system Sam King Operating System Support for Virtual Machines

Final Performance Results Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Conclusion Existing OS abstractions sufficient, slow Fast interception of signals and exceptions Expose power of underlying hardware Type II VMM CAN be as fast as type I Questions? Sam King Operating System Support for Virtual Machines

Operating System Support for Virtual Machines Related Work User-Mode-Linux SUNY Palladium Mach, Exokernel, L4 Wisconsin Wind Tunnel Sam King Operating System Support for Virtual Machines

Further Areas of Improvement Asynchronous I/O Exception Handling Sam King Operating System Support for Virtual Machines