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[sean mooney <2067757@xxxxxxxxxxxxxxxxxx>]

that not the reason, rhel based distos disabel nested virt on amd by
default if i recall correctly and you have to explicitly enabled it.

its not supported on RHEL and is considered tech preview as there are several know bugs.
intel is also not supported downstream for production workload however it much more mature and i bleive its  enabled by defuat.

nova is not filtering  out svm.

setting cpu_mode=none effectively is the same as cpu_mode=host-model

so either libvirt is disbalinging it or its a kernel  default issue.

in either case i don't think this is a valid nova bug.

** Changed in: nova
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/2067757

Title:
  AMD server do not support nested virtualization

Status in OpenStack Compute (nova):
  Invalid

Bug description:
  From Linux kernel v4.19 onwards, the nested KVM parameter is enabled
  by default for Intel and AMD. (Though your Linux distribution might
  override this default, here is the official documentation of this:
  https://www.kernel.org/doc/html/v5.7/virt/kvm/running-nested-
  guests.html

  We are using OpenStack Zed on CentOS 9 and the VM is running on AMD
  compute nodes, and the kernel version is: 5.14.0-386.el9.x86_64.

  When we created an instance on AMD server and set the "cpu_mode" to
  "none", we found that the "svm" feature is passed to the instance XML
  on libvirt, but when we execu "lscpu" inside the VM, we can not see
  the "svm" feature, so we could not create a L2 instance inside the VM.

  However, when we set the "cpu_mode" to "host-passthrough" and hard
  reboot the VM, the "svm" is set correctly within the VM.

  For intel servers, we can create nested instances by default, and the
  "cpu_mode" is also set to "none", and everything works well.

  We guess it might because of some CPU feature dependencies which cause
  this issue. Can you help us to take a look? Thanks

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