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For XEN we dont need Hardware Assisted support for running linux os. But why do we need that for KVM for running even linux based os.

Can Kvm be configured to support para virtualization.

Edit:

With full virtualization guests may not be aware that its being virtualized,and can degrade total performance,and in para virtualization guests are aware that its being virtualized and hence can result in improved performance is that so??

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There can be performance benefits to para-virtualization -- not in all cases. And there are security benefits to full virtualization. It's up to you to decide what is best for your environment. –  Aaron Copley Aug 18 '12 at 6:19
    
@AaronCopley Can you please specify how can there be security benefit for full virtualization? –  ananthan Oct 22 '12 at 15:26
    
No, I'm sorry. It's not the subject of this question. Feel free to start your own, though. (You can refer back to this one if you'd like.) –  Aaron Copley Oct 22 '12 at 18:51

2 Answers 2

up vote 6 down vote accepted

KVM provides full hardware virtualization, but you can use paravirtualized disk and network drivers (virtio). Most current Linux distributions will use them by default provided you've configured them when setting up the VM.

Since you expanded your question, I'll expand my answer.

In full hardware virtualization, every component of the virtual PC appears to be a physical PC and the guest OS uses the same device drivers as it would if it were on a physical PC made of the same hardware. This can be slow because the hypervisor has to emulate common hardware for the benefit of the guest.

In paravirtualization, guests can use specially written drivers for some performance-critical devices (like the disk and network drivers) to improve performance back to near bare-metal numbers. The paravirtualized driver, instead of talking to emulated hardware, talks (almost) directly to the native hardware.

The disk and network drivers are generally the first to be paravirtualized, since they provide the greatest performance benefit. Other devices can be paravirtualized as well, though doing so doesn't provide much actual real-world benefit.

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KVM supports para-virtualization for certain drivers, but not for the entire Guest. They explicitly define themselves as a full virtualization solution for Linux.

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