Xen and the Art of Virtualization

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Xen and the Art of Virtualization
Paul Barham, Boris Dragovic, Keir Fraser, Steven
Hand, Tim Harris, Alex Ho, Rolf Neugebauer, Ian
Pratt, Andrew Warfield
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Apology / Disclaimer
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Why Virtualise?

• Consolidate machines
• Isolate performance
• Stay flexible

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HARDWARE
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???
HARDWARE
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Linux
WinXP
???
HARDWARE
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Linux
WinXP
Mirage
???
HARDWARE
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Linux
WinXP
Mirage
Virtual Machine Monitor
HARDWARE
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How to Build a VMM 1 Emulation
EMULATOR PROCESS
Physical memory
Guest App
Guest App
Virtual MMU
Virtual System Calls
Guest Kernel
Virtual CPU
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate
Guest Kernel
Guest App
EMULATOR PROCESS
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate
Guest Kernel
Guest App
EMULATOR PROCESS
add eax, ebx
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate
Guest Kernel
Guest App
EMULATOR PROCESS
outb al
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate
Guest Kernel
Guest App
EMULATOR PROCESS
outb al
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate
Guest Kernel
Guest App
EMULATOR PROCESS
handle_sysenter
sysenter
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 2 Trap and Emulate

• for(i 0 i lt 256 i)
• mangle_pagetable_entry(ptesi)
• 256 traps into the emulator
• Severe performance penalty

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How to Build a VMM 3 Dynamic Binary Translation
Rewritten Guest Kernel
Rewritten Guest App
TRANSLATOR PROCESS
Physical memory
Virtual MMU
Virtual System Calls
Normal OS
HARDWARE
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How to Build a VMM 3 Dynamic Binary Translation

• for(i 0 i lt 256 i)
• mangle_pagetable_entry(ptesi)

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How to Build a VMM 3 Dynamic Binary Translation

• pte_t new_ptes256
• for(i 0 i lt 256 i)
• new_ptesi mangled_entry(ptesi)
• register_new_ptes(new_ptes, 256)
• But when is this a safe alteration?

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How to Build a VMM 4 Xen

• Q. But when is this a safe alteration?
• A. Let the humans worry about that.
• Manually hack the OS paravirtualisation.

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Xen Founding Principles

• Minimally alter guest OS
• Don't disguise multiplexing
• Thusly, be faster than the competition

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VMWare Memory Management
VAS Pages
Physical frames
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VMWare Memory Management
VAS Pages
Physical frames
Page Table
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VMWare Memory Management
VAS Pages
Physical frames
Page Table (not really)
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VMWare Memory Management
VAS Pages
Physical frames
Shadow Page Table
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Xen Memory Management
VAS Pages
Physical frames
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Xen Memory Management
VAS Pages
Physical frames
Page Table
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VMWare I/O
Physical Memory
I/O Ports
NE2000 Model Rubbish NIC One op at a time Shared
buffers
Device Memory
Device Ports
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Xen I/O
Own Memory
Hypervisor
Async Queue --gt
lt-- Async Queue
Packet
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Xen I/O
Own Memory
Hypervisor
Async Queue --gt
lt-- Async Queue
Packet
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Xen I/O
Own Memory
Hypervisor
Async Queue --gt
lt-- Async Queue
Buffer
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Strawman Warning

• VMWare does that too
• Guest additions are basically paravirt

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Is it Any Good?