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xen-users
Re: [Xen-users] para virtualised and full virtualised
Petersson, Mats wrote:
[*snip*]
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".
Thanks for correcting me about the BIOS. So just to be clear,
the BIOS has absolutely nothing to do with it, right? The
processor is all that matters.
I know that Intel claims on their website that your BIOS must
support VT, but I've seen so many people suggest otherwise now
that I'm assuming that must be false.
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.
So you're NOT referring to the BIOS that is actually on your
motherboard in a flash rom here, right? You mean that you need
to have a separate BIOS resident on the hard disk (which will
appear as an executable called "hvmloader"). Could you point me
to where this is documented? I don't recall seeing it anywhere.
Also, what kind of special compiler would I need? Where could I
download it? This is the first time I've heard any mention of that.
(In case you haven't figured out, I've never actually used full
virtualization; I don't have hardware for it at the moment.
I'm running Xen with paravirtualization, but I'd like to go
ahead and figure this HVM stuff out for the future. =) )
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.
Okay, cool. =)
Oh! One more thing though. At the moment, Xen does not support
AMD processors with VT, right? It only works with Intel VT
enabled processors. Is that right?
Thanks for replying,
-GM
[*snip*]
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