Gash Has No Privileges
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The document discusses kernel privileges, outlining what the kernel can do that user-level programs cannot, such as handling interrupts and executing privileged instructions. It explores the evolution of virtualization from early machines to modern hardware-assisted virtualization, emphasizing the challenges of efficient browser design and resource management. The document concludes with a call for modern browser development using advanced programming languages to enhance user experience while addressing safety and reliability concerns.
Gash Has No Privileges
- 2. Plan for Today Kernel Privileges How VirtualBox Really Works Browser Processes Demo PS2 Shell, Pipes, Redirects 1
- 3. Kernel Privileges What can the kernel (supervisor) do that user-level programs cannot? 2
- 4. Kernel Privileges What can the kernel (supervisor) do that user-level programs cannot? 1. Handle interrupts 2. Execute privileged instructions What instructions are privileged? 3
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- 7. GDT: Global Descriptor Table LDT: Local Descriptor Table Control memory segments MOV (control registers) What is in control registers (CR0)? 6
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- 11. x86 Protection Rings Ring 3 Rings 1 and 2: device drivers Ring 0 There’s nothing magic here: just 2 bits in a register that determine what instructions can execute! 10
- 12. Kernel Privileges What can the kernel (supervisor) do that user-level programs cannot? 1. Handle interrupts 2. Execute privileged instructions What happens when a user-level program attempts a privileged instruction? 11
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- 15. “Trap-and-Emulate” Early Virtual Machines (1960-2005) 1. Guest OS (running at user-level) attempts privileged instruction 2. Traps to host OS 3. Host OS trap handler switches to virtualization program (VMM) 4. VMM emulates privileged instruction in virtual environment SOSP 1973 14
- 16. Hardware-Assisted Virtualization VT-x (Intel) and AMD-V (2005/2006) vmrun Enter “Guest mode” Hardware-support for data structures for VM exit Return to “Host mode” Saves guest state in hardware data structures 15
- 17. How many processes should a browser create? Challenge for PS2 Exercise 1: what is the fewest number of processes you can have running on your machine? 16
- 18. 1990’s answer: 1 processes waste memory and CPU which are expensive and limited 17
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- 23. What should the 2010s answer be? 22
- 24. Apple iPhone 5C Five colors, 2 cores! Samsung Galaxy S4 Only two colors, but 4-8 cores! (+ loads of GPU cores) Note: the colors vs. cores tradeoff can probably be overcome by good engineering, but addressing the energy vs. cores tradeoffs require some theoretical advances also. 23
- 25. Humans should not be getting bored and grumpy waiting for their browser to render a page while cores are sitting idle! 24
- 26. “Start from Scratch” but constrained by using programming tools developed in the 1960s 25
- 27. 2010s answer: A modern browser should have enough threads to efficiently use all the machine resources available to provide human users with a good browsing experience! 26
- 28. Unfortunately, it is not (humanly) possible to build such a browser (in a way that will also be secure, robust, and reliable) using languages whose primary design goal was to fit on a 4K machine. 27
- 29. Why do Rust stickers have gears on them? Servo: the main reason Rust is being developed is so Mozilla can build a better browser! 28
- 30. Really starting from scratch is really hard… this is why getting Servo to the point where it can render a static page is cakeworthy! 29
- 31. PS2: The Good Auld SHell gash> gash> gash> gash> gash> gash> echo ‘Wha-hoo-wa!’ !! traceroute 128.143.22.36 id -p ray !! fsck; !mount -u VA! 30
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- 33. Charge Get started on PS2 You must work with one other person If you don’t have a teammate, stay after class and find one! Examine the processes running on your computer, have fun killing them (but backup your work first!) 32