1.
Virtualization Technology Overview
Liu, Jinsong
(jinsong.liu@intel.com)
SSG System Software Division

2.
Agenda
• Introduction
 history
 Usage model
• Virtualization overview
 cpu virtualiztion
 memory virtualization
 I/O virtualization
• Xen/KVM architecture
 Xen
 KVM
• Some intel work for Openstack
 OAT
2 2012/11/28

3.
Virtualization history
• 60s’ IBM - CP/CMS on S360, VM370, …
• 70’s 80s’ Silence
• 1998 VMWare - SimOS project, Stanford
• 2003 Xen - Xen project, Cambridge
• After that: KVM/Hyper-v/Parallels …
3 2012/11/28

4.
What is Virtualization
VM0 VM1 VMn
Apps Apps Apps
Guest OS Guest OS ... Guest OS
Virtual Machine Monitor (VMM)
Platform HW
Memory Processors I/O Devices
• VMM is a layer of abstraction
 support multiple guest OSes
 de-privilege each OS to run as Guest OS
• VMM is a layer of redirection
 redirect physical platform to virtual platform illusions of many
 provide virtaul platfom to guest os
4 2012/11/28

5.
Server Virtualization Usage Model
Server Consolidation R&D Production
App App App
…
OS OS OS
HW HW VMM VMM
HW HW
Benefit: Cost Savings
• Consolidate services Benefit: Business Agility and Productivity
• Power saving
Dynamic Load Balancing
Disaster Recovery
App App App App
1 2 3 4
App
App
… OS OS OS OS
OS OS VMM VMM
VMM
HW HW
VMM
CPU Usage CPU Usage
HW HW 90% 30%
Benefit: Lost saving
• RAS
• live migration
• relief lost • Benefit: Productivity
5 2012/11/28

6.
Agenda
• Introduction
• Virtualization overview
 CPU virtualization
 Memory virtualization
 I/O virtualization
• Xen/KVM architecture
• Some intel work for Openstack
6 2012/11/28

7.
X86 virtualization challenges
• Ring Deprivileging
 Goal: isolate guest OS from
• Controlling physical resources directly
• Modifying VMM code and data
 Ring deprivileging layout
• vmm runs at full privileged ring0
• Guest kernel runs at
• X86-32: deprivileging ring 1
• X86-64: deprivileging ring 3
• Guest app runs at ring 3
 Ring deprivileging problems
• Unnecessary faulting
• some privilege instructions
• some exceptions
• Guest kernel protection (x86-64)
• Virtualization holes
 19 instructions
• SIDT/SGDT/SLDT …
• PUSHF/POPF …
 Some userspace holes hard to fix by s/w approach
• Hard to trap, or
• Performance overhead
7 2012/11/28

8.
X86 virtualization challenges
VM0 VM0
1
VM0
2
Ring3 Guest Apps
Apps Guest Apps
Apps Guest Apps
Apps
Guest Kernel
Guest OS Guest Kernel
Guest OS Guest Kernel
Guest OS
Ring1
Ring0 Virtual Machine Monitor (VMM)
8 2012/11/28

9.
Typical X86 virtualization approaches
• Para-virtualization (PV)
 Para virtualization approach, like Xen
 Modified guest OS aware and co-work with VMM
 Standardization milestone: linux3.0
• VMI vs. PVOPS
• Bare metal vs. virtual platform
• Binary Translation (BT)
 Full virtualization approach, like VMWare
 Unmodified guest OS
 Translate binary ‘on-the-fly’
• translation block w/ caching,
• usually used for kernel, ~80% native performance
• userspace app directly runs natively as much as possible, ~100% native performance
• overall ~95% native performance
• Complicated
• Involves excessive complexities. e.g., self-modifying code
• Hardware-assisted Virtualization (VT)
 Full virtualization approach assisted by hardware, like KVM
 Unmodified guest OS
 Intel VT-x, AMD-v
 Benefits:
• Closing virtualization holes in hardware
• Simplify VMM software
• Optimizing for performance
9 2012/11/28

10.
Memory virtualization challenges
• Guest OS has 2 assumptions
 expect to own physical memory starting from 0
• BIOS/Legacy OS are designed to boot from address low 1M
 expect to own basically contiguous physical memory
• OS kernel requires minimal contiguous low memory
• DMA require certain level of contiguous memory
• Efficient MM management, e.g., less buddy overhead
• Efficient TLB, e.g., super page TLB
• MMU virtualization
 How to keep physical TLB valid
 Different approaches involve different complication and overhead
10 2012/11/28

11.
Memory virtualization challenges
VM1 VM2 VM3 VM4
1
Guest 2
Pseudo 3
Physical 4
Memory 5
Hypervisor
5
Machine 1
Physical
Memory 2
3 4
11 2012/5/13

12.
Memory virtualization approaches
• Direct page table
 Guest/VMM in same linear space
 Guest/VMM share same page table
GVA
• Shadow page table
 Guest page table unmodified
• gva -> gpa
 VMM shadow page table
• gva -> hpa
 Complication and memory overhead Guest
page table
• Extended page table
 Guest page table unmodified
• gva -> gpa
Direct Shadow
• full control CR3, page fault
 VMM extended page table page table GPA page table
• gpa -> hpa
• hardware based
• good scalability for SMP
• low memory overhead Extended
• Reduce page fault VMexit greatly page table
• Flexible choices
 Para virtualization
• Direct page table
• Shadow page table
 Full virtualization HPA
• Shadow page table
• Extended page table
12 2012/11/28

13.
Shadow page table
Page
Directory
• Guest page table remains PTE
unmodified to guest
PDE
 Translate from gva -> gpa Page
Table
• Hypervisor create a new vCR3
page table for physical
Virtual
 Use hpa in PDE/PTE
Physical
 Translate from gva -> hpa
 Invisible to guest Page
Directory
PTE
PDE
Page
Table
pCR3
13 2012/11/28

14.
Extended page table
Guest CR3 EPT base pointer
Guest Guest Physical Address Extended
Guest Linear Page Page Host Physical
Address Tables Tables Address
• Extended page table
 Guest can have full control over its page tables and events
• CR3, INVLPG, page fault
 VMM controls Extended Page Tables
• Complicated shadow page table is eliminated
• Improved scalability for SMP guest
14 2012/11/28

15.
I/O virtualization requirements
Interrupt
Register Access
Device CPU
DMA Shared
Memory
• I/O device from OS point of view
 Resource configuration and probe
 I/O request: IO, MMIO
 I/O data: DMA
 Interrupt
• I/O Virtualization require
 presenting guestos driver a complete device interface
• Presenting an existing interface
• Software Emulation
• Direct assignment
• Presenting a brand new interface
• Paravirtualization
15 2012/11/28

16.
I/O virtualization approaches
• Emulated I/O
 Software emulates real hardware device
 VMs run same driver for the emulated hardware device
 Good legacy software compatibility
 Emulation overheads limit performance
• Paravirtualized I/O
 Uses abstract interfaces and stack for I/O services
 FE driver: guest run virtualization-aware drivers
 BE driver: driver based on simplified I/O interface and stack
 Better performance over emulated I/O
• Direct I/O
 Directly assign device to Guest
• Guest access I/O device directly
• High performance and low CPU utilization
 DMA issue
• Guest set guest physical address
• DMA hardware only accept host physical address
 Solution: DMA Remapping (a.k.a IOMMU)
• I/O page table is introduced
• DMA engine translate according to I/O page table
 Some limitations under live migration
16 2012/11/28

17.
Virtual platform models
Hypervisor Model Host-based Model Hybrid Model
Guest Guest Guest
Apps Apps ULM
Apps Apps Apps
DM
Service
Preferred Guest Guest Preferred VM Guest
OS OS ULM OS OS OS
DM DR
P M DR P M
Host
Hypervisor U-Hypervisor
OS P LKM M
DR DM N
P Processor Mgt code DR Device Driver N NoDMA
M Memory Mgt code DM Device Model
17 2012/11/28

18.
Agenda
• Introduction
• Virtualization
• Xen/KVM architecture
• Some intel work for Openstack
18 2012/11/28

19.
Xen Architecture
HVM Domain HVM Domain
Domain 0 DomainU (32-bit) (64-bit)
XenLinux64 Unmodified Unmodified
OS OS
(xm/xend)
Models
Control
Device
Panel
3P 3D
XenLinux64
Drivers
Drivers
FE
FE
Front end Virtual
0D
Virtual driver
Guest BIOS Guest BIOS
Backend
Drivers
Virtual Platform Virtual Platform
1/3P Native
Device
Drivers VM Exit VM Exit
Callback / Hypercall
0P
Inter-domain Event Channels
Control Interface Scheduler Event Channel Hypercalls
Processor Memory I/O: PIT, APIC, PIC, IOAPIC
Xen Hypervisor
19 2012/11/28

20.
KVM Architecture
Windows Linux
Guest Guest
Qemu-kvm
Non Root
Root
VMCS VMCS VMCS
vCPU vMEM vTimer
Linux Kernel vPIC vAPIC vIOAPIC
KVM module
20 2012/11/28

21.
Agenda
• Introduction
• Virtualization
• Xen/KVM architecture
• Some intel work for Openstack
21 2012/11/28

22.
Trusted Pools - Implementation
User specifies ::
OpenStack App
App
App
App
App App
Host
Mem > 2G agent
Disk > 50G OS OS
GPGPU=Intel Hypervisor / tboot
EC2 API
trusted_host=trusted Create VM HW/TXT
Tboot-
Scheduler Enabled
Create TrustedFilter
OSAPI
Query
Report
Attest
untrusted
trusted/
Query API Attestation
Server
Host Agent API
Privacy OAT-
Query API
CA
Based
Attestation Appraiser
Service Whitelist
Whitelist API
DB