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EDV Dave

Nested VMS Unraid 6.7.2 VMX Performance

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Hello guys,


is it possible to activate VMX for Qemu in Unraid 6.7.2.?


Iam using Passtrough-Mode with the "kvm_intel nested=1" in Autostart to run MS Hyper-V 2016 on my Unraid Setup.

Inside the HyperV 2016 Server i can use nested VMs without hassle when HyperV option enabled and pc-i440fx .

But the performance is absolutely horrible and everthing is lagging  behind.


When i switch do QMEU64 / KVM  CPU mode the Performance of my MS Hyper Server increases drastically. But the Intel VD-X Features are not exposed to it anymore, hence i cannot run nested VMs.


How can i expose VMX to my HyperV Host running on QEMU CPU Mode.


I Found the following:






Somehow it should be possible to make the CPUS Features visible to the VM.


The XML commands above, mentioned by Siwat, do not work anymore.

Error: XML error: Non-empty feature list specified without CPU model


Cpu Mode "custom" does not exist anymore. But there is a mode called "Host-Model".


How can i use QEMU emulated CPU Cores for my MS HyperV Server and passtrough the VMX Features to its VMS for nested Virtualization.


best regards



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Just adding +vmx to the cpu features supported worked for me with a nested guest on  a MacOS VM. Like this:

    <qemu:arg value='-cpu'/>
    <qemu:arg value='Penryn,vendor=GenuineIntel,kvm=on,+invtsc,vmware-cpuid-freq=on,+vmx'/>


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On 7/30/2019 at 2:25 PM, Jagadguru said:

Just adding +vmx to the cpu features supported worked for me with a nested guest on  a MacOS VM. Like this:

    <qemu:arg value='-cpu'/>
    <qemu:arg value='Penryn,vendor=GenuineIntel,kvm=on,+invtsc,vmware-cpuid-freq=on,+vmx'/>


in here?

  <cpu mode='host-passthrough' check='none'>
    <topology sockets='1' cores='10' threads='2'/>


My CPU is Sandy Bridge EP though, should it still be Penryn? E5 2650

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At the very end of the XML.  It's for when you use a QEMU emulated CPU like the OP. Yours should be Penryn if you're running MacOS in a VM. 


What OS are you trying to run in your VM? And what guest within that guest are you trying to run? And with what Virtualization software (within the VM)?

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where can i find the right xml file guys?

my vm xml only got this short cpu section:



  <vcpu placement='static'>24</vcpu>
    <vcpupin vcpu='0' cpuset='0'/>
    <vcpupin vcpu='1' cpuset='12'/>
    <vcpupin vcpu='2' cpuset='1'/>
    <vcpupin vcpu='3' cpuset='13'/>
    <vcpupin vcpu='4' cpuset='2'/>
    <vcpupin vcpu='5' cpuset='14'/>
    <vcpupin vcpu='6' cpuset='3'/>
    <vcpupin vcpu='7' cpuset='15'/>
    <vcpupin vcpu='8' cpuset='4'/>
    <vcpupin vcpu='9' cpuset='16'/>
    <vcpupin vcpu='10' cpuset='5'/>
    <vcpupin vcpu='11' cpuset='17'/>
    <vcpupin vcpu='12' cpuset='6'/>
    <vcpupin vcpu='13' cpuset='18'/>
    <vcpupin vcpu='14' cpuset='7'/>
    <vcpupin vcpu='15' cpuset='19'/>
    <vcpupin vcpu='16' cpuset='8'/>
    <vcpupin vcpu='17' cpuset='20'/>
    <vcpupin vcpu='18' cpuset='9'/>
    <vcpupin vcpu='19' cpuset='21'/>
    <vcpupin vcpu='20' cpuset='10'/>
    <vcpupin vcpu='21' cpuset='22'/>
    <vcpupin vcpu='22' cpuset='11'/>
    <vcpupin vcpu='23' cpuset='23'/>
    <type arch='x86_64' machine='pc-i440fx-3.1'>hvm</type>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
      <vendor_id state='on' value='none'/>
  <cpu mode='host-passthrough' check='none'>
    <topology sockets='1' cores='12' threads='2'/>


you probably edit some qemu config xml right? not the vm itself

Edited by EDV Dave

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OK it worked. Just added your Lines within the "domain" tag:



    <memballoon model='none'/>
  <seclabel type='dynamic' model='dac' relabel='yes'>
    <qemu:arg value='-cpu'/>
    <qemu:arg value='Penryn,vendor=GenuineIntel,kvm=on,+invtsc,vmware-cpuid-freq=on,+vmx'/>




Performance is way better now and nested VMS do start with QEMU Penryn now, but still not performing as well as when i just tick QMEMU CPU without speccifying Penryn type.


 Are there other choices?


best regards

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Thanks this helped me a lot. Made a big difference to get it like that. Now just to set up static huge pages on my second numa node.

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