I agree.  The patch is a nop.  I just got overly paranoid.  The whole
thing is just very prone to bugs.

So do we need a patch for .23 or not?

; it does
seem perfectly acceptable though for the mm code to use kmap or vmap
(not kmap_atomic) internally somewhere in the pagetable code.

i386 does it all the time for highmem pagetables in fact.

-Andi