Constructing Services with Interposable Virtual Hardware

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Constructing Services with Interposable Virtual
Hardware

• Author Andrew Whitaker, Richard S. Cox, Marianne
  Shaw, and Steven D. Gribble
• Presenter Huajing Li

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Outline

• Study Motivation
• Overview of a previous VMM, Denali
• An extensible VMM µDenali
• Key feature of µDenali event routing framework
• Application studies
• Discussion

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Study Motivation

• Resurgence in popularity of VMMs
• A powerful platform for new system services
• Simplify problem solution
• Novel applications
• Applied in relevant study areas
• A promising application of VMM as a virtual
  machine service platform.

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Design Limitation of Current VMMs

• Little support was given for developing and
  deploying virtual machine services
• Non-programmable
• Non-extensible
• Self-tailored blackbox system without standard
  interfaces
• Similar with many previous scenarios
• No standards or commonly-aware protocols are
  agreed
• Inter-operability is a serious issue
• Unnecessary efforts are devoted in repeated works

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Interoperability Requirements

• Goal give programmers efficient facilities to
  develop services that manipulate the virtual
  machine interface.
• What functionality should VMM provide to VM
  services?
• Interpose events (messaging across VMs)
• Extend hardware (resources)
• More?
• How to support the previous two key services?
• Intuitively, as the solution we developed for
  distributed systems, we need to create a
  sub-system to coordinate between parts of the
  system.
• Messaging protocol and supportive network
• Resource assignment and management

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Overview of a previous VMM, Denali

• The novel VMM proposed in the paper is based on a
  previous VMM Denali.
• Type-I VMM
• Design goal support a large scale of VMs
• Strategically modifies the virtual architecture
  (interrupt processing, handling non-virtualizable
  instruction, and timers)
• Support NetBSD OS

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Denali Architecture

• Virtual devices bridge between physical devices
  and VM usable interfaces.
• Virtual CPU
• Virtual MMU
• Virtual timers
• Virtual network
• Virtual disk

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An extensible VMM µDenali

• Denali neither supports interposition nor
  extension.
• µDenali is an updated version of Denali, in which
  three basic functions of a VMM are handled in a
  clean separated manner
• Physical resource management
• Device namespace virtualization
• Virtual hardware event trapping and routing
• Recall the two interoperability requirements
  discussed above. The separation of the three
  functions can perfectly meet them.

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Event Routing Infrastructure in µDenali

• Events (typed messages) are associated with
  destination ports.
• The port mapping is configurable, managed by VMM.
• A hardware of a VM (child) can be bound to
  another VM (parent) so that the parent VM has the
  privilege to interpose the childs device.

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µDenali Architecture
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The NetBSD Interposition Library

• Describe a set of operations that a parent VM can
  perform on a child.
• A protocol which consists of a set of downcalls
  sent to children VMs as well as a set of
  responses returned by children.
• Security concern global events are not included
  in the protocol.
• The set of operations
• Virtual machine control
• I/O device interposition
• Exposing µDenali internal state
• Tracking and logging non-deterministic events

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Event Routing

• A framework to receive, route and deliver typed
  messages encoded by VMs.
• An interval messaging network
• Ports are created as protected communication
  channel between VMs.
• Each virtual device in each VM has a set of
  standardized ports associated with it.
• A link between a child VMs port and its parent
  VMs port establishes the message delivery
  connection.

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µDenali Port Tables

• A centralized control by VMM
• Question alternative approach?
• Pros and Cons
• µDenali VMM maintains a table of port
  capabilities on behalf of each VM.
• Port capability includes receive, send and
  send-once rights.
• Stated in the paper From the point of view of
  µDenali, a virtual machine is simply a port
  table.
• It is the parent VMs responsibility to
  initialize the port table of a child VM.

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µDenali Port Queues and Message Buffers

• Messages are not stored by VMM
• Simplify the message delivery process.
• VMM is not involved in the checkpoints or
  recovery of a specific VM.
• Each virtual device which owns message receiving
  port implements its own port queue.
• µDenali asks each VM to maintain ring buffers to
  store messages.

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Example Port Table and Buffers
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Applications

• As use studies of µDenali
• Internet suspend / resume
• Drop-in network services
• Continuous rejuvenation
• Disk and swap device extensions
• Supported by the interposition library provided
  by µDenali, the above services are easy to be
  implemented.

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Discussion

• Summary this paper addresses the problem of lack
  of support for developing cooperative virtual
  machine services in current popular VMMs and
  proposes µDenali to solve it.
• Question What is the desired level of
  interoperability and extensibility?
• µDenali supports VMM-managed (centralized)
  resource and event sharing.

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Thank you!