Masha at 00:37, 2 December 2007

2007-12-02T00:37:01Z

← Older revision		Revision as of 00:37, 2 December 2007
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	~~(Note: This is just a placeholder while I organize the information I have and create the images)~~

	== QEMU ==		== QEMU ==
	* Where does it fit in OS architecture?		* Where does it fit in OS architecture?
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	* If the TLB misses, the kernel gets called		* If the TLB misses, the kernel gets called
	* Locality of reference: for data and for code, can be spatial and temporal		* Locality of reference: for data and for code, can be spatial and temporal

	~~--[[User:Masha\|Masha]] 00:30, 22 November 2007 (EST)~~

Masha: Initial outline commit

2007-11-22T05:30:07Z

Initial outline commit

New page

(Note: This is just a placeholder while I organize the information I have and create the images)

== QEMU ==
* Where does it fit in OS architecture?
* Simply a procdess, so: [Image 1 goes here]
* If a shell is running in QEMU, it is not seen from the regular terminal
* Quite analogous to the J(ava) V(irtual) M(achine)

== Virtual Machine Monitor ==
* What do you emulate?
** QEMU emulates ''everything'' (like PowerPC binaries for Intel x86 chip) [Image 2 goes here]
* If data coming in is the Linux kernel, it expects to be run in supervisor mode, so QEMU has to emulate supervisor mode (otherwise cannot process privileged instructions)
* If a program in user mode executes a privileged instruction, a software interrupt gets generated, and the kernel is called to look up the trap table
** Example: division by zero
* We would like to emulate any hardware we want; so, why not just dump code directly on the CPU without QEMU in-between?
** Cannot do this, because regular Linux kernel will catch the interrupts
*** One possible way to get around this is to take out privileged instructions from binaries (essentially rewrite them)

== Hypervisor ==
* The kernel's kernel [Image 3 goes here]

=== Ring Model ===
* Unix only has two rings: kernel = 0, user = 3 [Image 4 hoes here]
* If hypervisor runs in -1, we can run multiple operating systems on top of the hypervisor [Image 5 goes here]
* The hypervisor is part of the mechanism that prevents pirated games from playing on the Play Station 3
* Hypervisor does not really affect performance, because it is tacked onto the I/O part of system calls
* Translating memory access from applications in user spaces means switching to kernel (supervisor), and then again from supervisor to hypervisor
* If running multiple operating systems, hypervisor designates one operating system to be the host or root access
* "Server consolidation" - using machines to the best of their abilities to conserve power

=== "Blue Pill" ===
* When an attacker comes in, they have to run as a user process
* To hide, try to modify kernel code to camouflage processes
* Put security code in hypervisor - only good if attacker does not get there first
* Apparently, Windows kernel can actually tell if it has been virtuatlized, because there is one process that cannot be changed - the clock, so determine virtualization by checking the timing of I/O and interrupts
* "Halting problem"

== MMU ==
* How do we translate addresses? For some process, looking at address 2000 actually means looking at 8420
* Every instruction accessing memory has to perform this translation
* There exist tables that keep these - in page intervals (a pages is approximately a 4KB block)
* MMU needs a cache (very fast) to keep these tables
* MMU also requires a special kind of memory called associative memory (not like computers' main memory)
** Content-based access, not address-based
* TLB - translational lookaside buffer is the table with tags (directly on MMU), <64K
* If the TLB misses, the kernel gets called
* Locality of reference: for data and for code, can be spatial and temporal

--[[User:Masha|Masha]] 00:30, 22 November 2007 (EST)

Scheduling - Revision history

Masha at 00:37, 2 December 2007

Masha: Initial outline commit