CS533 Concepts of Operating Systems

Class 9

Virtualization and Exo-Kernels

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Virtualization and Fault Isolation

Do VMMs support fault isolation?o If so, how?

Is the fault isolation problem they solve the same as the one tackled by micro-kernel architectures?

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Multi-tasking

At what granularity do VM monitors support multitasking?

o How does it differ from conventional multitasking?o How do virtualized CPUs differ from threads/processes?

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Virtualization and Hardware

Why is it difficult to virtualize the x86 CPU?

What hardware support would be useful for virtualization?

Does virtualization hide any characteristics of the real hardware?

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True vs Para Virtualization

Why would you want true virtualization?

Why would you want para-virtualization?

Why is it harder to virtualize CPUs with hardware specified page tables than software managed TLBs?

Xen is not transparent to a guest OS. In what ways can the OS distinguish execution on Xen from execution on bare hardware?

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VMMs vs Micro-Kernels

Is Disco a micro-kernel?

Is Xen a micro-kernel?

Do micro-kernels do virtualization?

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Exo-kernel

What is the difference between virtualization and secure multiplexing?

o Do Xen or Disco do secure multiplexing?o Does Exokernel create virtual machines?o How do the approaches differ?

Is Exo-kernel a micro-kernel?o What abstractions does it support?

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Exo-kernel

Does Exokernel support the process abstraction? Does the Exokernel "paravirtualize" privileged

instructions? How does Exokernel’s visible revocation relate to

scheduler activations?o How does it differ from Xen and Disco in this respect?

How does PCT relate to LRPC?o What is the difference between synchronous and

asynchronous PCT?

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Exo-kernel

How does Exo-kernel use hardware support to improve performance?

How are "software caches" used to improve performance?

How is "downloaded code" used to improve performance?

o How does this relate to Sandboxing?o How does this relate to SPIN?