From: Anton Blanchard <anton@samba.org>

Paul wrote a patch to use some of the rmap infrastructure to flush TLB
entries on ppc64.  When testing it we found a problem in vmalloc where it
sets up the pte -> address mapping incorrectly.  We clear the top bits of
the address but then forget to pass in the full address to
pte_alloc_kernel.  The end result is the address in page->index is
truncated.

I fixed it in a similar way to how zeromap_pmd_range etc does it.  I'm
guessing no one uses the rmap hooks on vmalloc pages yet, so havent seen
this problem.