CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

Question

I have the same issue as here, but the solution does not work to me. Every time I want to create or run a VM with virt-manager, I get the same message:

Error al iniciar dominio: configuración no soportada: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor 

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 89, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 125, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 82, in newfn
    ret = fn(self, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1508, in startup
    self._backend.create()
  File "/usr/lib/python2.7/site-packages/libvirt.py", line 1069, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: configuración no soportada: CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor 

However, when appying the fix from the mentiones thread then I get:

Error al iniciar dominio: internal error: process exited while connecting to monitor: Could not access KVM kernel module: Permission denied
2018-03-13T22:43:10.555542Z qemu-system-x86_64: failed to initialize KVM: Permission denied

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 89, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 125, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 82, in newfn
    ret = fn(self, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1508, in startup
    self._backend.create()
  File "/usr/lib/python2.7/site-packages/libvirt.py", line 1069, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: internal error: process exited while connecting to monitor: Could not access KVM kernel module: Permission denied
2018-03-13T22:43:10.555542Z qemu-system-x86_64: failed to initialize KVM: Permission denied

I've also tried as root, but same result.

My system is Parabola GNU/Linux-libre (Arch-based) x86_64

Solution 1

Try rebooting the host machine.

This seems weird but it is just happened to me. I am using debian stretch and While installing a gust OS(some distribution of ubuntu) on KVM for the first time after installation, I got the same alert. I shutdown the host machine leaving the issue unresolved and the next day while trying again, I got no error at all. Meanwhile I did absolutely nothing. There is a possibility that KVM needs a restart for complete installation or to collect necessary data. Though I am not sure about arch but you can give it a try before proceeding for another solution.

Solution 2

I had the same issue, and the problem was that libvirt could not access /dev/kvm. So you need to make sure, the user has the right permissions to access the device node, e.g., by running chown root.kvm /dev/kvm;chmod 660 /dev/kvm.

I suppose that it just tries the machine configuration and returns this error, when anything does not work, because it thinks the configuration is the problem.

Comments

[Amitav Pajni]

How did you set the CPU configuration? Try setting it to "Predeterminado del hipervisor".

[Megver83]

same thing, I'm getting the second error again

[Amitav Pajni]

It's probably something specific to your distro, then. Try selecting a specific CPU type matching your actual CPU generation, or use a different Linux distribution.

[Megver83]

and how did you solve it?

[allo]

chmod on /dev/kvm

[user323094]

+1 helped me. As a bonus, I noticed that my new machine restarts really fast.