Re: [Xen-users] Intel 2 core duo question

["Ulrich Windl" <ulrich.windl@xxxxxxxxxxxxxxxxxxxx>]

On 2 Nov 2006 at 6:31, Art Fore wrote:

> Have a machine with intel 2 core duo (7600) processore. It is a del
> latitude D820. I get the followmessage from the xm dmesg output:
>
> VMX disabled by Feature Control MSR.
>
> This is on both cores. I believe it is the vanderpool part disabled,, am
> I right? What is this Feature Control? And how do you enable it if that
> is what it is.  I looked in the bios settings, but did not see anything
> I recognize for enabling the vanderpool thing.

>From the Intel manual "IA-32 Intel® Architecture Software Developer´s Manual
Volume 3B: System Programming Guide, Part 2" (downloadable PDF):
19.7 ENABLING AND ENTERING VMX OPERATION

Before system software can enter VMX operation, it enables VMX by setting
CR4.VMXE[bit 13] = 1. VMX operation is then entered by executing the VMXON
instruction.
VMXON causes an invalid-opcode exception (#UD) if executed with CR4.VMXE = 0. 
Once
in
VMX operation, it is not possible to clear CR4.VMXE (see Section 19.8). System
software
leaves VMX operation by executing the VMXOFF instruction. CR4.VMXE can be 
cleared
outside of VMX operation after executing of VMXOFF.
VMXON is also controlled by the IA32_FEATURE_CONTROL MSR (MSR address 3AH).
This MSR is cleared to zero when a logical processor is reset. The relevant bits
of the MSR are:
o Bit 0 is the lock bit. If this bit is clear, VMXON causes a general-protection
exception. If
the lock bit is set, WRMSR to this MSR causes a general-protection exception. 
Once
the
lock bit is set, the MSR cannot be modified until a power-up reset condition.
System BIOS
can use this bit to provide a setup option for BIOS to disable support for VMX. 
To
enable
VMX support in a platform, BIOS must set bit 2 (see below) as well as the lock
bit.
o Bit 2 enables VMXON. If this bit is clear, VMXON causes a general-protection
exception

Regards,
Ulrich


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