kern/59993: nvmm: support nested virt

["campbell+netbsd%mumble.net@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         59993
>Category:       kern
>Synopsis:       nvmm: support nested virt
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 10 22:50:01 +0000 2026
>Originator:     Taylor R Campbell
>Release:        current, 11, 10, 9, ...
>Organization:
The NetNVMM Virtual Machine Monitor Recursion, Inc.
>Environment:
>Description:
It would be nice if nvmm supported nested virtualization, so that you can develop and debug nvmm inside a VM.

Paper on how to do this:

https://www.usenix.org/legacy/events/osdi10/tech/full_papers/Ben-Yehuda.pdf
>How-To-Repeat:
try to use nvmm from inside qemu -accel nvmm
>Fix:
Yes, please!