hypervisor architecture installs the virtualization layer directly on a clean

Hypervisor architecture installs the virtualization

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hypervisor architecture installs the virtualization layer directly on a clean x86-based system. Depending on the needs and goals of the computer, some alternative techniques which provide for handling sensitive and privileged instructions to virtualize the physical resources are discussed as follows: 1) Full Virtualization: In this approach, kernel codes are translated to replace non-virtualizable instructions with new sequences of instructions that have the required effect on the virtual hardware. The guest OS is not aware it is being virtualized and requires no modification. The hypervisor simulates several logical instances of completely independent virtual computers possessing its own virtual resources. It translates all operating system instructions on the fly and caches the results for future use, while user level instructions run unmodified at native speed. The virtual resources included I/O ports and DMA channels. Therefore, each virtual machine can run any operating system supported by the underlying hardware. [5]. In Full Virtualization, the I/O devices are allotted to the guest machines by imitating the physical devices in the virtual machine monitor; interacting with these devices in the virtual environment are then directed to the real physical devices either by the host operating system driver or by the "hypervisor driver [5]". Therefore, Full virtualization can offer the best isolation and security for virtual machines; it simplifies migration and portability as the same guest OS instance can run on a virtualized or native hardware. 2) Paravirtualization: In this approach, the running guest OS should be modified in order to be operated in the virtual
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environment. Unlike full virtualization, Paravirtualization is a subset of server virtualization, which provides a thin software interface between the host hardware and the modified guest OS. Paravirtualization involves modifying the OS kernel to replace non-virtualizable instructions with hypercalls that communicate directly with the virtualization layer hypervisor. Moreover, the virtual machine monitor is simple which allows paravirtualization to achieve performance closer to non-virtualized hardware. Xen [4] is an example of Paravirtualization. It virtualizes the processor and memory using a modified Linux kernel and virtualizes the I/O using custom guest OS device drivers. Modifying the guest OS to enable Para-virtualization is relatively easy, compared to Full Virtualization. 3) Hardware Assisted Virtualization: Hardware assisted virtualization is a new CPU execution mode. In the new CPU execution mode, the VMM is allowed to run in root mode. Moreover, this mode allows privileged and sensitive calls to automatically trap to the hypervisor, removing the need for either binary translation or Paravirtualization. When Intel and AMD released their processors with inbuilt hardware which supports virtualization, the mode has recently gains attention. In addition, the hardware support virtualization architecture creates a trusted "root mode" and an untrusted "non-root mode". [6] in this mode. There is an example AMD-V [7] which supports hardware assisted virtualization.
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  • Fall '16
  • Sir Adnan
  • virtual machine

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