[libvirt-users] Help With Nested Virtualization

[Martin Kletzander]

On Thu, Sep 01, 2016 at 12:11:17PM +0200, Kashyap Chamarthy wrote:
>On Wed, Aug 31, 2016 at 12:48:33PM +0200, Martin Kletzander wrote:
>> On Mon, Aug 29, 2016 at 09:42:17PM -0400, Brandon Golway wrote:
>> > (Copied from my post on the Arch Linux forums:
>
>[...]
>
>> > Can someone clue me in on what the issue is?
>> >
>> > Here's the entire XML config for the FreeNAS VM
>> >
>> > [code]<!--
>> > WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
>> > OVERWRITTEN AND LOST. Changes to this xml configuration should be made
>> > using:
>> >  virsh edit FreeNAS_10
>> > or other application using the libvirt API.
>> > -->
>> >
>>
>> Just as I see you grabbed it from the place where it is stored, you
>> should rather instead do 'virsh dumpxml FreeNAS_10', or remove the
>> comment above.  Otherwise it steers other users to believing that
>> mangling with internal XML files is safe.
>
>Yeah, or use the `virt-xml` tool (comes as part of `virt-install`
>package).  To pass-through host CPU to the level-1 guest:
>
>	$ virt-xml FreeNAS_10 --edit --cpu host-passthrough,clearxml=yes
>
>If you issue this while the guest is running, it'll take affect on next
>reboot.
>
>> > <domain type='kvm'>
>> >  <name>FreeNAS_10</name>
>> >  <uuid>ea816b85-7685-495a-bc97-28a882f190d7</uuid>
>> >  <title>FreeNAS v10</title>
>> >  <description>Nightly Alpha Test Releases</description>
>> >  <memory unit='KiB'>6340608</memory>
>> >  <currentMemory unit='KiB'>6340608</currentMemory>
>> >  <vcpu placement='static'>4</vcpu>
>> >  <os>
>> >    <type arch='x86_64' machine='pc-i440fx-2.6'>hvm</type>
>> >    <bootmenu enable='no'/>
>> >  </os>
>> >  <features>
>> >    <acpi/>
>> >    <apic/>
>> >    <vmport state='off'/>
>> >  </features>
>> >  <cpu mode='host-passthrough'/>
>>
>> Although what you did should be enough for the nested virt to work, I
>> have just an idea to try out.  I can't try it because I don't have
>> nested virt turned on for the module and don't want to reboot now.
>
>Assuming you're talking about the physical host, you don't need a reboot
>of the host :-) You can simply:
>
>    $ sudo rmmod kvm-intel
>    $ echo "options kvm-intel nested=y" > /etc/modprobe.d/dist.conf
>    $ sudo modprobe kvm-intel
>

Unless:
  $ zgrep -i kvm_intel /proc/config.gz
  CONFIG_KVM_INTEL=y

Maybe I could switch to =m when I'm building the next kernel.

>> But
>> if you have new enough libvirt, you should be able to do:
>>
>> <cpu mode='host-passthrough'>
>>  <feature policy='require' name='vmx'/>
>> </cpu>
>>
>> Also check that you are not missing the kvm_intel module in the L1 guest
>> kernel and other similar non-nested troubleshooting steps as well.
>
>Yeah.  If the L1 guest has the /dev/kvm character device, then he's good:
>
>    $ file /dev/kvm
>    /dev/kvm: character special (10/232)
>
>
>--
>/kashyap
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