So you are running an unknown version (I have no idea what "B" means), and furthermore an as yet unreleased version. That means that anything that breaks is to be expected.
I'm getting a page fault panic on ...
If you want assistance debugging it, we need WAY MORE information. At the minimum a stack trace with register dumps, and a description of what the system was doing. If you are running a pre-release version, debugging it probably also requires showing us the source code of where the problem occurred.
Isnt the point of copyout to lock down the pages during the copy?
Describing the purpose of a significantly large part of the kernel in a half dozen words is not going to work. It's way more complex that that.
It seems in 12 the page in user space isn't locked down.
If in general the pages weren't pinned or locked during the page out IO operation, then fundamentally nothing would work. That seems exceedingly unlikely. It is also the kind of elementary mistake that no seasoned kernel developer would make, and that would not get through reviews. Now, it is possible that there is a bug in the logic (wouldn't be the first one, and won't be the last one), but such a generalization makes it laughable.
I've found some other threads where it's outlined that stuff that's worked for 20 years no longer works because none of the corporate sponsors care about it. One of the "improvements" in 12.
Sorry, if you want to make paranoid accusations, you need to give us some evidence. Extraordinary claims require extraordinary evidence. The idea that no corporate sponsors care about basic functionality of the OS (which paging is) is nonsense. As is your mental concept that FreeBSD development is driven by decisions of corporate sponsors. I don't know whether it has become clear to you that this is not Linux, and the sociology and economics of Linux does not apply here.
Please show us which threads, what has been broken, and which "corporate sponsors" used to keep it running. Failing that, my explanation for your behavior here in this thread is that you are just being disruptive and trolling.