RE: [Xen-users] para virtualised and full virtualised

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Grok Mogger
> Sent: 01 December 2006 03:13
> To: anant
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] para virtualised and full virtualised
> 
> anant wrote:
> > Hi 
> > my system is showing as if its para virtualised. I think 
> intel vt isn't
> > included but i would like to know can i install windows 
> OperatinG System
> > over para virtualised system or its possible only with 
> fully virtualised...I
> > am new to linux and xen .Any help would be appreciated... 
> > thanks
> 
> Hey, I hope this'll help,
> 
> 1) My understanding is that you can only install Windows as a 
> Guest OS if you are running "fully virtualized" Xen software.
> 
> 2) My understanding about running Xen "fully virtualized" is 
> that it requires 3 things.
>     i) Your processor must support Virtualization Technology 
> (VT) (called "Intel VT" by Intel or "AMDV" by AMD).
>     ii) Your BIOS must support VT.  If it does, you'll have some 
> options to turn VT on and off from within the BIOS.

Currently, AMD doesn't support "switching off" AMD-V, so it's not
dependant on any BIOS features - it's only dependant on having "the
right model of processor". 

>     iii) Xen must be compiled to support VT.  I think I recall 
> seeing some instructions about how to compile Xen to support 
> full virtualization somewhere in the Xen 3.0 manual...

There are a few things that need to be done to build for HVM (VT) mode,
but the actual Xen kernel supports HVM by and of itself without any
settings or adjustments - just build the code and it's there. 

The things that need special attention is the fact that to boot a
fully-virtualized domain (guest), you'll need a BIOS that loads the OS
itself (just like you need for a REAL machine). The BIOS requires a
special compiler to be downloaded. I believe this is now an ERROR rather
than a WARNING, but I'm not 100% sure. Either way, if you're not certain
if this works, go to <xen-source-dir>/tools/firmware and do "make". If
it builds ok and you have a hvmloader executable in the hvmloader
direectory, then you've got all the tools. If that's not the case, then
you'll need to follow the instructons from the makefile. 

> 
> 3) I believe you can determine whether or not your processor 
> supports Intel VT by going to looking at the text file 
> "/proc/cpuinfo".  In that file, you will see a line that starts 
> with the word "flags".  The line will most likely also contain a 
> list of 3 or 4 letter abbreviations that (to me at least) mostly 
> don't make a whole lot of sense.  If you see "vmx" in that list, 
> supposedly that means that you have a VT enabled processor.  I 
> have read this a few places on the internet, but am a little 
> skeptical myself.

For AMD processors, you'll need to look for "svm", "vmx" is the Intel
name for this feature. 

> 
> If anyone else can confirm or refute what I've written here, 
> please do.
> 
> 
> Thanks,
> - GM
> 
> BTW - I saw someone suggest that you might run Windows as a 
> Guest OS on a paravirtualized Xen system by actually running a 
> paravirtualized *Linux* Guest OS (as you're probably already 
> doing), and then using qemu to run Windows from within that 
> Linux Guest.  I have not tried this myself and have no idea how 
> well it might work.  (I've never even used qemu)

That'll be POSSIBLE, and it's got a few advantages over the "obvious"
solution of running QEMU in Dom0 - mainly that Dom0 should be used only
for the minimal amount of work, as it's priority is higher than other
domaoms  (by default at least), and thus other domains may starve if
Dom0 is very busy. 

--
Mats
> 
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