[Xen-devel] Re: pv_ops dom0 kernel and VT cpu extensions

[Christian Tramnitz <chris.ace@xxxxxxx>]

Gerry Reno wrote:
> I compiled a pv_ops dom0 kernel from Jeremy's latest git tree and 
> upgraded Xen to 3.4.1 following one of Boris' blog entries.  From the 
> Xen perspective everything seems to work as expected.  But, I want to be 
> able to run both Xen and KVM existing guests in a single cloud on a farm 
> of VT-enabled machines.  So after booting into the new pv_ops dom0 
> kernel as a test I tried starting one of my KVM guests.  It ran 
> extremely slow so I knew immediately that it wasnt' using the VT 
> acceleration.  I then looked at /proc/cpuinfo and saw that the VT cpu 
> flag (svm on this machine) was not there.  The machine has a VT 
> processor and hardware virtualization is enabled in the BIOS and I 
> rebooted to check with a regular kernel and it of course the guest runs 
> with VT acceleration there.
> My question is how can I get pv_ops dom0 kernel or Xen 3.4.1 to pass the 
> cpu VT flags through so that existing KVM guests will run with cpu VT 
> acceleration at full speed?
You need to start the pvops kernel on bare metal (without Xen) to make 
use of VT. dom0 is already a (privileged) guest (of Xen), so the 
hardware assisted virtualization interface is simply not accessible at 
this point anymore...
Best regards,
   Christian


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