Formal Requirements for Virtualizable Third Generation Architectures – Popek & Goldberg With thanks to Alfred Bratterud for pointing me. Formal Requirements for. Virtualizable Third. Generation Architectures. Gerald J. Popek. University of California, Los Angeles and. Robert P. Goldberg. The Popek and Goldberg virtualization requirements are a set of conditions sufficient for a computer architecture to support system virtualization efficiently. They were introduced by Gerald J. Popek and Robert P. Goldberg in their article “Formal Requirements for Virtualizable Third Generation Architectures”.

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What exactly is a virtual machine? What does a virtual machine monitor do? Beneration how do we now whether a given piece of hardware can support virtualization or not? There are currently a number of viewpoints suggesting what a virtual machine is, how it ought to be constructed, and what hardware and operating system implications result…. Though of course we need to dig further and understand what is implied by the three words efficientisolatedand duplicate.

To explain these, the authors introduce the notion of a virtual machine monitor…. This is the question the vast majority of the paper is dedicated to. Such machines have a processor, and linear uniformly addressable memory. The processor can operate in supervisor mode, or in user mode. Some instructions are only available in supervisor mode.

Formal Requirements for Virtualizable Third Generation Architectures | the morning paper

The location parameter l gives the absolute address that corresponds to the apparent address zero, and the bounds parameter b gives the absolute size of the virtual memory. Suppose an instruction produces some address awe check and then find the true address as follows:.

In this model, for simplicity, we have departed slightly from most common ivrtualizable systems by assuming it to be active in the supervisor as well as user mode. This difference will not be important to the proof of our result. Note also that all references made by the processor to memory are assumed to be relocated.

A trapsuch as the memorytrap above, automatically saves the current state of the machine and passes control to a pre-specified control routine by changing the PSW to the values specified in E[1]. Key to understand whether or not it is possible to virtualize a given piece of hardware is to divide the requiremenrs into groups. In particular, privileged instructions are those that do not trap when the processor is in supervisor mode, but do trap a privileged instruction trap when in user mode.


Privileged instructions are independent of the virtualization process. They are merely characteristics of the machine which may be determined from reading the principles of operation.

Popek and Goldberg virtualization requirements

Note, however, that the way we have defined privileged instructions requires them to trap. Merely NOPing the instruction without trapping is insufficient. Sensitive instructions may be either control sensitive, or behaviour sensitive.

Control sensitive instructions are those that affect or can affect control over system resources — in our eequirements model the only such resource rsquirements memory. A control sensitive instruction attempts to change the amount of resource memory available, or change processor mode, without going through a memory trap.

A behaviour sensitive instruction is one whereby the effect of its execution is dependent on the value of the relocation bounds register location in real memory or processor mode. An instruction that is not sensitive is innocuous. A virtual machine monitor is fhird control program comprising a dispatcher, an allocator, and a set of interpreters, one per privileged instruction.

The location of the control program dispatcher is placed in the program counter at E[1], it directs execution to the allocator or interpreters as needed. The allocator decides what system resources are to be provided e. The allocator will be invoked by the dispatcher whenever an attempted execution of a privileged instruction in a virtual machine environment occurs which would have the effect of changing the machine resources associated with that environment.

Attempting to reset the R relocation-bounds register is the primary example in our skeletal model. If the processor were to be treated as a resource, a halt would be another. A virtual machine monitor [that satisfies the three properties of grneration, resource control, and equivalence] may be constructed if the set of sensitive instructions for that computer is a subset of the privileged instructions.

The proof of this statement is given in the paper and the appendices — requirememts rests on showing a one-one homomorphism f between real machine states and virtual machine states, and that if the arcbitectures machine halts in state S, then the virtual machine halts in state f S.

The final step is an existence argument i. Furthermore, recursive virtualization a VM that runs a copy of itself under the VMM is possible if a a VMM can be constructed for the hardware as above, and b the VMM does not have any timing dependencies. However, those features which have been assumed are fairly standard ones, so the relationship between the sets of sensitive and privileged instructions is the only constraint.


It is a very modest one, easy to check. Further, it is also a simple matter for hardware designers to use as a design requirement. Going forward I architectuures that we should let requirement 1 from Popek-Goldberg go. If we consider something like uKVM as a replacement for Qemu we end up with a significantly more secure and performant system.

Geneartion took requiremennts comment and my it into a blogpost. You are commenting using your WordPress. You are commenting using your Twitter account. You are commenting using atchitectures Facebook account.

Notify me of new comments via email. Notify me of new posts via email. This site uses Akismet to reduce spam. Learn how architecfures comment data is processed. With thanks to Alfred Bratterud for pointing me at this paper. What is a Virtual Machine? A virtual machine is taken to be an efficient, isolated duplicate of the real machine.

Formal Requirements for Virtualizable Third Generation Architectures

To explain these, the authors introduce the notion of a virtual machine monitor… What is a Virtual Machine Monitor? A virtual machine monitor VMM does three things: It provides a duplicateor essentially identical to the original machine, environment for programs.

This statement rules out traditional emulators and complete software interpreters simulators from the virtual machine umbrella. It is in complete control of system resources memory, peripherals, and the like. This requires two conditions: A virtual machine is the environment created by the virtual machine monitor. Does my Hardware Support Virtualization? Suppose an instruction produces some address awe check and then find the true address as follows: The job of the interpreters is to simulate the instruction that trapped.

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