This adds support for highmem pages poisoning and verification to the
debug-pagealloc feature for no-architecture support.

[akpm@linux-foundation.org: remove unneeded preempt_disable/enable]
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>