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RE: [Xen-users] No Full Virtualisation with Intel Core 2 Duo T5500 Mobile CPU?


> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Karl Stevens
> Sent: 12 February 2007 19:18
> To: Falko Tesch
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] No Full Virtualisation with Intel 
> Core 2 Duo T5500 Mobile CPU?
> Hash: SHA1
> Falko Tesch wrote:
> > Hello,
> > 
> > I have some interesting issue with Intel VT CPU and XEN 3.0.2:
> > 
> > I'm running XEN 3.0.2 on a MSI Fuzzy 945GM2 Mainboard
> > 
> (http://www.msi.com.tw/program/products/ic/ic_detail.php?prod_
> no=4) with
> > a Intel Core 2 Duo Mobile CPU (T5500).
> > 
> > When booting the mainboard BIOS says it found a EM64T CPU, which is
> > AFAIK the code for a Intel CPU with Virtualisation Technologie.
> > But whether Linux nor XEN detects this CPU as a VT CPU.

Just to clarify, EM64T is Intel's name for x86-64 (aka AMD64), so it's
the 64-bit extensions to the x86 architecture. This is NOT directly
related to Intel's VT. 

> > 
> > Who's right, the mainboard or Linux?
> Probably both.  Intel allows the BIOS to disable the VT 
> instructions at
> boot time.

Since you're looking at different features, we can't say one is right or
wrong. Obviously, the core-duo processor shouls support VT and 64-bit
> If the BIOS allows you to enable it (most manufacturers leave it
> disabled by default) you will need to power-cycle the machine after
> doing so (just rebooting won't work - the machine needs to be off for
> the option to be enabled properly.)

This is correct, you will need to enable the feature in BIOS (or
technically speaking "Not set the disable bit"!) in the BIOS during
startup. Since this is a "can't clear" bit, once it's been written, it
can't be reset in software, you'll have to power-cycle as Karl says. 

It's worth noting also that there are BIOS's that don't allow this bit
to be turned on/off - they just lock it without giving the user any
options to change the setting. 

> - -Karl
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