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List:       kvm
Subject:    Re: Regarding KVM
From:       Zhen-Hua Li <lizhenhua.dev () gmail ! com>
Date:       2011-12-29 2:57:00
Message-ID: CAEk7JKa9nmdwFq0yTXYoWEft+DMgBbtVU+nF0bnUHtPER8iQag () mail ! gmail ! com
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In short, when you running qemu and enabled KVM, kvm only gives
virtual cpu and gets the commands from your vm and give them to VT.
KVm does  not have other hardware.  The hardware are provided by qemu
or other vms.


> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On Behalf Of \
>                 David Mair
> Sent: Wednesday, 28 December, 2011 09:43
> To: adapa.ajith@gmail.com
> Cc: kvm@vger.kernel.org
> Subject: Re: Regarding KVM
> 
> Hi
> 
> On 12/27/2011 03:25 AM, Ajith Adapa wrote:
> > Hi,
> > 
> > I am new to KVM stuff and had very BASIC (might be lame even) doubts
> > regarding KVM.
> > 
> > As per the various diagrams I have gone through in internet my
> > understanding is KVM is an hypervisor on top of which all VMs run.
> > 
> > In case of FULL VIRTUALIZATION .. KVM will be directly running on top
> > of HARDWARE and VMs will be running on top of KVM .
> > In that case we dont need any support of other linux modules or subsystems ?
> > 
> > vm1 ... vmn
> > --------------
> > > KVM      |
> > --------------
> > Hardware
> 
> Not in my experience. kvm is drivers on a host kernel which has other drivers in \
> order to function (at least to boot) and a user-space (at least qemu instances). \
> kvm does provide I/O virtualization to the extent that host devices you only want \
> to be used in a guest can be ignored without host drivers and only operated from \
> the guest as-if a guest device with guest drivers but there will still be things \
> like I/O port access trapping and interrupts will happen on host processors at any \
> juncture so presumably quickly routed by kvm behavior to service routines after \
> switching to a suitable guest context, though I'm no expert on the code. 
> > Actually I am very much intrested in networking component of
> > virtualization. So does KVM provides any specific support for
> > networking in case of virtualization ?
> 
> You can take a host NIC and use it's drivers in a guest to operate it.
> You can use tap interfaces for a guest and bridge them to host interfaces which can \
> include bridged physical NICs or not and/or use host IP stack configuration to \
> route guest traffic from its own IP network to any reachable by the host. On most \
> of my kvm hosts I have bridges br0, br1 and br8 to simulate the vmnet0 (bridged - \
> physical network access), vmnet1 (host only - isolated guests with host \
> connectivity) and vmnet8 (NAT - routing from a host only network to anything \
> reachable by the host) configurations you get on many default vmware \
> configurations. I tried the I/O device virtualization quite a while ago and it \
> wasn't reliable enough and, although I'm sure it's much improved, with the \
> configuration I use I've never needed to try again. 
> > Sorry if there is any developer guide for KVM will be more helpful for me.
> 
> --
> David.
> --
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