[RESEND PATCH v6] x86/fpu: Trying to fix writing PKRU through ptrace

[Kyle Huey]

Hello Linus,

I've been trying since July to get this regression that was introduced in
5.14 fixed. This is my third time submitting this version of the patch in the
last two months. Both prior submissions have not received any comments from
(nor have they been applied by) the x86 maintainers. I don't really know
what else to do at this point beyond "complain to the management" as it
were.

I appreciate anything you can do to unjam things here.

- Kyle