Numa fault is a method which help to achieve auto numa balancing.
When such a page fault takes place, the page fault handler will check
whether the page is placed correctly. If not, migration should be
involved to cut down the distance between the cpu and pages.

A pte with _PAGE_NUMA help to implement numa fault. It means not to
allow the MMU to access the page directly. So a page fault is triggered
and numa fault handler gets the opportunity to run checker.

As for the access of MMU, we need special handling for the powernv's guest.
When we mark a pte with _PAGE_NUMA, we already call mmu_notifier to
invalidate it in guest's htab, but when we tried to re-insert them,
we firstly try to map it in real-mode. Only after this fails, we fallback
to virt mode, and most of important, we run numa fault handler in virt
mode.  This patch guards the way of real-mode to ensure that if a pte is
marked with _PAGE_NUMA, it will NOT be mapped in real mode, instead, it will
be mapped in virt mode and have the opportunity to be checked with placement.
Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>