SLIDE 1
CSC 256/456: Operating Systems
Microkernels
John Criswell University of Rochester
1
Onwards to user-space!
2
Microkernels John Criswell University of Rochester 1 Onwards to - - PowerPoint PPT Presentation
Microkernels John Criswell University of Rochester 1 Onwards to - - PowerPoint PPT Presentation
CSC 256/456: Operating Systems Microkernels John Criswell University of Rochester 1 Onwards to user-space! 2 Microkernels 3 Monolithic Kernel (aka Everything and the Kitchen Sink) Application Application Libraries Commands
SLIDE 2
SLIDE 3
Microkernels
3
SLIDE 4
Monolithic Kernel (aka Everything and the Kitchen Sink)
Application Programs Libraries Commands
Device Driver
Application Programs OS System Call Interface
Device Driver Device Driver
Driver Interface
…
Monolithic Kernel Module
- Process Management
- Memory Management
- File Management
- Device Mgmt Infrastructure
…
4
SLIDE 5
Monolithic Kernel Limitations
❖ Poor security ❖ Buffer overflow gains access to everything! ❖ Poor reliability ❖ Bug in kernel can affect unrelated subsystems ❖ Difficult to restart faulty subsystem
5
SLIDE 6
Processes Don’t Have This Problem
❖ Isolated memory ❖ Communication via ❖ Pipes ❖ Explicitly shared memory ❖ Self-contained programs ❖ No access to irrelevant data
structures
Web Server Email Client MP3 Player
6
SLIDE 7
Could kernel components be processes?
7
SLIDE 8
Microkernel
❖ Move kernel functionality into user-space processes ❖ File systems ❖ Networking subsystem ❖ Drivers ❖ Kernel provides ❖ Protection ❖ Communication mechanisms
8
SLIDE 9
Microkernel
9
File System TCP/IP Ethernet Driver Disk Driver Process Credentials Address Space IPC Terminal Driver Web Server Email Client MP3 Player Page Replacement Video Game Interrupt Handler
User Mode Kernel Mode
SLIDE 10
Advantages of Microkernels
❖ Faults are localized ❖ Bug in network code doesn’t corrupt disk data ❖ Easier to improve reliability ❖ Can monitor and restart processes (e.g., filesystem) ❖ Easier to apply security techniques ❖ Randomization and re-randomization (Guiffruida) ❖ Apply memory safety or type-safe language to critical
processes
10
SLIDE 11
Disadvantages of Microkernels
❖ Communication overhead ❖ Semantics of message passing affects performance ❖ What is placed in user-space affects performance ❖ User/Kernel boundary crossing overhead ❖ Context switching overhead ❖ Monolithic libraries are always available ❖ User-space service may not have CPU when needed ❖ TLB Flush when switching page table pages 11
SLIDE 12
Microkernel Advantages are Not Magic
❖ Reliability must be designed and built ❖ File system process crash still catastrophic ❖ Restart of critical processes must be designed and
built
❖ Security is still an issue ❖ Exploited file system process can access any file ❖ Exploited network process can read all packets
12
SLIDE 13
Mach
❖ Developed at Carnegie Mellon University in the 80’s ❖ Memory management design influenced modern OS
design
❖ Goal: separate policy from mechanism
13
SLIDE 14
Example: Mach
❖ User-level memory management ❖ trusted/protected by the kernel ❖ kernel provides the basic protection mechanism ❖ user-level memory manager handles page loading; decides replacement policy
14
SLIDE 15
Microkernel Failures
❖ Windows NT family ❖ Original Windows NT had microkernel design ❖ By Windows 2000, functionality moved into kernel ❖ Mac OS X ❖ Based on NextStep which is based on Mach + 4.4BSD ❖ BSD sub-systems moved into kernel; live alongside Mach ❖ Essentially two kernels living in the same space
15
SLIDE 16
Microkernel Successes
❖ QNX (real-time operating system kernel) ❖ Symbian (mobile operating system) ❖ L4 ❖ Major work to reduce microkernel overheads ❖ Can run Linux with L4Linux ❖ seL4: Fully verified variant
16
SLIDE 17
Hypervisors and Virtual Machines
17
SLIDE 18
Virtual Machines
❖ Run multiple OS instances ❖ Migrate OS instances from one machine to another ❖ Software compatibility when hardware changes
18
Windows Mac OS X Linux ??? Hardware
SLIDE 19
Compiler Translation
❖ Translate binary code (Original VMWare) ❖ Translate virtual code (JVM, OS/360)
19
Windows Mac OS X Linux Original VMWare Hardware
SLIDE 20
Para-Virtualizaiton
❖ Modify OS to interface with lower-level hypervisor ❖ Efficient but requires OS changes
20
Windows Mac OS X Linux Original Xen Hardware
SLIDE 21
Hardware Virtualization
❖ Hardware provide new privilege layer under OS ❖ Efficient ❖ Compatible ❖ Requires new hardware
21
Windows Mac OS X Linux Xen, Hyper-V Hardware
SLIDE 22
Credits
❖ Some slides based on slides from previous year ❖ Slides only to be used for instruction at the University of
Rochester
22