6.033 Spring Lecture #6. Monolithic kernels vs. Microkernels Virtual Machines spring 2018 Katrina LaCurts

Transcription

1 6.033 Spring 2018 Lecture #6 Monolithic kernels vs. Microkernels Virtual Machines 1

2 operating systems enforce modularity on a single machine using virtualization in order to enforce modularity + build an effective operating system 1. programs shouldn t be able to refer to (and corrupt) each others memory virtual memory 2. programs should be able to communicate 3. programs should be able to share a CPU without one program halting the progress of the others bounded buffers (virtualize communication links) threads (virtualize processors) today: running multiple OSes at once (and dealing with kernel bugs) 2

3 Virtual Machines virtual machine running guest OS virtual machine running guest OS physical hardware problem: how to (safely) share access to physical hardware? 3

4 Virtual Machines VMM runs in kernel-mode on hardware virtual machine running guest OS virtual machine running guest OS virtual machine monitor (VMM) physical hardware 4

5 guest OS guest OS U/K page table U/K page table virtual machine monitor (VMM) physical hardware U/K,,, VMM s goal: virtualize hardware 5

6 guest virtual guest OS guest OS address U/K U/K guest physical address virtual machine monitor (VMM) physical hardware U/K,,, host physical address 6

7 guest OS load guest OS guest OS VMM intercept! guest OS VMM host + guest virtual -> guest physical VMM guest physical -> host physical host physical hardware host guest virtual -> host physical 7

8 guest OS load guest OS guest OS VMM intercept! guest virtual -> guest physical VMM guest physical -> guest OS VMM host physical + physical hardware in modern hardware, the physical hardware is aware of both s, and performs the translation from guest virtual to host physical itself 8

9 guest OS guest OS U/K page table U/K page table virtual machine monitor (VMM) physical hardware U/K,,, VMM s goal: virtualize hardware 9

10 source: bugzilla.kernel.org, count of all bugs currently marked NEW, ASSIGNED, REOPENED, RESOLVED, VERIFIED, or CLOSED, by creation date source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see 10

11 monolithic kernels: no enforced modularity within the kernel itself Application Basic interprocess communication, virtual memory, scheduling, file server, device drivers, network, Hardware 11

12 microkernels: enforce modularity by putting subsystems in user programs Application application IPC device driver network Basic interprocess communication, virtual memory, scheduling Hardware 12

13 Virtual Machines allow us to run multiple isolated OSes on a single physical machine, similar to how we used an OS to run multiple programs on a single CPU. VMs must handle the challenges of virtualizing the hardware (examples: virtualizing memory, the U/K bit). Monolithic kernels provide no enforced modularity within the kernel. Microkernels do, but redesigning monolithic kernels as microkernels is challenging. 13

14 Virtual Machines (in the host OS model, there was actually a host OS) virtual machine running guest OS virtual machine running guest OS virtual machine monitor (VMM) 14

15 MIT OpenCourseWare Computer System Engineering Spring 2018 For information about citing these materials or our Terms of Use, visit: