Comment 21 for bug 1813165

'nested' parameter for kvm_intel module controls whether you're able to run nested configurations and it is enabled by default, it doesn't say anything about whether your configuration is nested or not.

Could you please describe your environment? In case it is nested, it will look like:
L0(host) Linux 5.4.0 .... with KVM
L1(guest) Linux xxxx with KVM
L2(nested guest) Linux xxxx

Note that L2 in this scenario is running "inside" L1 and that's why it is nested.

Also, it is important to know if L1 or L2 in this configuration are UEFI booted, it is not very important how you boot the host (L0).