CMA area is now managed by the separate zone, ZONE_MOVABLE, to fix many
MM related problems.  In this implementation, if CONFIG_HIGHMEM = y,
then ZONE_MOVABLE is considered as HIGHMEM and the memory of the CMA
area is also considered as HIGHMEM.  That means that they are considered
as the page without direct mapping.  However, CMA area could be in a
lowmem and the memory could have direct mapping.

In ARM, when establishing a new mapping for DMA, direct mapping should
be cleared since two mapping with different cache policy could cause
unknown problem.  With this patch, PageHighmem() for the CMA memory
located in lowmem returns true so that the function for DMA mapping
cannot notice whether it needs to clear direct mapping or not,
correctly.  To handle this situation, this patch always clears direct
mapping for such CMA memory.

Link: http://lkml.kernel.org/r/1512114786-5085-4-git-send-email-iamjoonsoo.kim@lge.comSigned-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>