Revision as of 17:48, 30 November 2010

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Paper

"The Turtles Project: Design and Implementation of Nested Virtualization"

Authors:

Muli Ben-Yehuday +
Michael D. Day ++
Zvi Dubitzky +
Michael Factor +
Nadav Har’El +
Abel Gordon +
Anthony Liguori ++
Orit Wasserman +
Ben-Ami Yassour +

Research labs:

+ IBM Research – Haifa

++ IBM Linux Technology Center

Website: http://www.usenix.org/events/osdi10/tech/full_papers/Ben-Yehuda.pdf

Video presentation: http://www.usenix.org/multimedia/osdi10ben-yehuda [Note: username and password are required for entry]

Background Concepts

Before we delve into the details of our research paper, its essential that we provide some insight and background to the concepts and notions discussed by the authors.

Virtualization

In essence, virtualization is creating an emulation of the underlying hardware for a guest operating system, program or a process to operate on. [1] Usually referred to as virtual machine, this emulation which includes a guest hypervisor and a virtualized environment, only gives an illusion to the guest virtual machine to make it think that its running directly on the main hardware. In other words, we can view this virtual machine as an application running on the host OS.

The term virtualization has become rather broad, associated with a number of areas where this technology is used like data virtualization, storage virtualization, mobile virtualization and network virtualization. For the purposes and context of our assigned paper, we shall focus our attention on hardware virtualization within the context of operating systems.

Hypervisor

Also referred to as VMM (Virtual machine monitor), is a software module that exists one level above the supervisor and runs directly on the bare hardware to monitor the execution and behaviour of the guest virtual machines. The main task of the hypervior is to provide an emulation of the underlying hardware (CPU, memory, I/O, drivers, etc.) to the guest virtual machines and to take care of the possible issues that may rise due to the interaction of those guest virtual machines among one another, and the interaction with the host hardware and operating system. It also controls host resources.

Nested virtualization

Nested virtualization is the concept of recursively running one or more virtual machines inside one another. For instance, the main operating system (L1) runs a VM called L2, in turn, L2 runs another VM L3, L3 then runs L4 and so on.

Para-virtualization

Trap and emulate model

A vitualization model based on the idea that when a guest hypervisor attempts to execute, gain or access privilged hardware context, it triggers a trap or a fault which gets handled or caught by the host hypervisor. The host hypervisor then determines whether this instruction should be allowed to execute or not. Then based on that, the host hypervisor provides an emulation of the requested outcome to the guest hypervisor. The x86 systems discussed in the Turtles Project research paper follows this model.

The uses of nested virtualization

Compatibility

A system could provide the user with a compatibility mode for other operatng systems or applications. An example of this would be the Windows XP mode thats available in Windows 7, where Windows 7 runs Windows XP as a virtual machine.

Cloud computing

A cloud provider, more fomally referred to as Infrastructure-as-a-Service (IAAS) provider, could use nested virtualization to give the ability to customers to host their own preferred user-controlled hypervisors and run their virtual machines on the provider hardware. This way both sides can benefit, the provider can attract customers and the customer can have freedom implementing its system on the host hardware without worrying about compatibility issues.

The most well known example of an IAAS provider is Amazon Web Services (AWS). AWS presents a virtualized platform for other services and web sites such as NetFlix to host their API and database on Amazon's hardware.

Security

Migration/Transfer of VMs

Nested virtualization can also be used in live migration or transfer of virtual machines in cases of upgrade or disaster recovery. Consider a scenarion where a number of virtual machines must be moved to a new hardware server for upgrade, instead of having to move each VM sepertaely, we can nest those virtual machines and their hypervisors to create one nested entity thats easier to deal with and more manageable. In the last couple of years, virtualization packages such as VMWare and VirtualBox have adapted this notion of live migration and developed their own embedded migration/transfer agents.

Testing

Using virtual machines is convenient for testing, evaluation and bechmarking purposes. Since a virtual machine is essentially a file on the host operating system, if corrupted or damaged, it can easily be removed, recreated or even restored since we can can create a snapshot of the running virtual machine.

Protection rings

Research problem

What is the research problem being addressed by the paper? How does this problem relate to past related work?

Contribution

What are the research contribution(s) of this work? Specifically, what are the key research results, and what do they mean? (What was implemented? Why is it any better than what came before?)

Critique

.. to be continued ..

The good

The non stop evolution of computers entices intricate designs that are virtualized and harmonious with cloud computing. The paper contributes to this belief by allowing consumers and users to inject machines with their choice of hypervisor/OS combination that provides grounds for security and compatibility. The sophisticated abstractions presented in the paper such as shadow paging and isolation of a single OS resources authorize programmers for further development and ideas which use this infrastructure. For example the paper Accountable Virtual Machines wraps programs around a particular state VM which could most definitely be placed on a separate hypervisor for ideal isolation.

The bad

COnclusion

Bottom line, the research showed in the paper is the first to achieve efficient x86 nested-virtualization without altering the hardware, relying on software-only techniques and mechanisms. They also won the Jay Lepreau best paper award.

References

[1] Tanenbaum, Andrew (2007). Modern Operating Systems (3rd edition), page 569.

@@ Line 102: / Line 102: @@
 === The bad ===
+=== COnclusion ===
 Bottom line, the research showed in the paper is the first to achieve efficient x86 nested-virtualization without altering the hardware, relying on software-only techniques and mechanisms. They also won the Jay Lepreau best paper award.
 =References=
 [1] Tanenbaum, Andrew (2007).'' Modern Operating Systems (3rd edition)'', page 569.