VMX disabled by Feature Control MSR

[Guillaume Thouvenin <guillaume.thouvenin@bull.net>]

Hello,

 I already posted a message about this problem on this mailing list but
I went more deeply in the analysis of the problem and I'd like to have
your opinion. 

 The problem is: I have a processor (pentium D) that supports the VT
technology but when I boot Xen I have the following message:

(XEN) VMX disabled by Feature Control MSR.

 Here is how I understand that. Xen is using the CPUID instruction to
identify the processor functionality. This is done in
arch/x86/hvm/vmx/vmx.c:start_vmx(). As VMXON is controlled by the
IA32_FEATURE_CONTROL we must test the lock bit (bit0) and the bit2. I
found in the intel documentation that if the bit2 is clear, VMXON
causes a general-protection exeption. In our case, we stop the
start_vmx() function and display the message VMX disabled by feature
control MSR. 

  Thus my question is: What to do to set the bit 2 of the
IA32_FEATURE_CONTROL to 1? Is it only possible by using the option in
the BIOS menu (and it's not present in mine) or is it possible to set it
to 1 before switching in protected mode when Xen is booting. For exemple
somwhere in arch/x86/boot/x86_64.S?


 Thanks for your help,

Guillaume