[Bug 246168] Ubuntu 20.04 KVM / QEMU Failure with nested FreeBSD bhyve

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246168

--- Comment #10 from Peter Grehan <grehan at FreeBSD.org> ---
I used a laptop-class CPU when trying the repro (core i5-8250U). In particular,
there is a difference in VT-x features as reported by the L1 guest:

  VT-x: PAT,HLT,MTF,PAUSE,EPT,UG,VPID

vs your system:

  VT-x: PAT,HLT,MTF,PAUSE,EPT,UG,VPID,VID,PostIntr

The one of interest here is that KVM is emulating APIC-virtualization
(VID,PostIntr).

One thing to try is to disable this feature in the L1 guest. In
/boot/loader.conf, put an entry 

hw.vmm.vmx.use_apic_vid=0

After (re)booting the L1 guest, the status of this parameter can be checked
with:

# sysctl hw.vmm.vmx.cap.virtual_interrupt_delivery
hw.vmm.vmx.cap.virtual_interrupt_delivery: 0          <- should be zero

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