> I had Virtualbox just boot the physical Windows partition while Linux was running. Which is totally fine!

I had no idea that this was possible, and I learned something new today. Thank you!

I think Windows refused to do that at some point? So I booted the physical Linux partition from Windows if I needed both at the same time. That's on a laptop that otherwise almost always ran Linux.

Yeah. That is a valid use. I mean, this is how I installed Windows to begin with, from Linux via QEMU, onto my other hard drive. I did reboot and test it out, and it worked just fine.