Question

3) There are different approaches for virtualization. List two architectures for virtualization, draw the architecture figures and briefly explain their differences. [10 points)

Answer 1

These are the types of virtualization or architecture of virtualization:

• Bare Metal / Native

In this type of virtualization, the hypervisors run directly on the machine's hardware to control it and manages the guest operating systems present. Just as depicted in the digram above, guest OS runs a level above the hypervisor.

• Hosted

In this type of virtualization, the hypervisors run on a layer of Host Operating System. That is, hypervisors are deployed over the host OS and Guest OS is installed above the layer of Hypervisor.

We use the machine's hardware and the operating system to run any virtualization software (VMWare) or any hypervisor and inside these softwares, we use our virtual machines or a guest OS.

Approaches to Virtualization:

(i) Full Virtualization using Binary Translation -

User apps directly have access to the hardware. In Full virtualization technique, the VM uses Binary translation to virtualize both sensitive and non-virtualizable instructions sent by the Guest OS. The Guest OS is not aware that is is virtualized and believes that it is the only system present in the machine.

The performance may be low as instructions need to be translated to binary and reverse.

Example: ESXi, MS Virtual Server, etc.

(ii) Para Virtualization using Hypercalls-

In this, we modify the OS kernel to send hypercalls to the hypervisor or the virtualization layer so that we can avoid the binary translations. Even critical instructions can be passed through hypercalls.

It is an attempt to increase the performance as the translations are not required here. Also, the Guest OS is aware that the system is virtualized.

Example: Xen, IBM LPAR

(iii) Hardware assisted Virtualization-

VIrtualization technologies such as Intel's VTx, and AMD-V enables an option for VMM to work below the Ring 0 Layer having the root mode priveleges. The guest OS is run in the Ring 0 where root privelges are not given. Therefore, the sensitive information or priveleged instructions are automatically caught by the VMM or hypervisor and are handled by the hardware which removes the requirement of hyper calls or binary translations.

Examples: VMWare workstation, Xen Centre, etc.

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