powerpc/64s/hash: Allow MAP_FIXED allocations to cross 128TB boundary

While mapping hints with a length that cross 128TB are disallowed,
MAP_FIXED allocations that cross 128TB are allowed. These are failing
on hash (on radix they succeed). Add an additional case for fixed
mappings to expand the addr_limit when crossing 128TB.

Fixes: f4ea6dcb08ea ("powerpc/mm: Enable mappings above 128TB")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/slice.c

@@ -418,7 +418,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	unsigned long high_limit;
 
 	high_limit = DEFAULT_MAP_WINDOW;
-	if (addr >= high_limit)
+	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
 		high_limit = TASK_SIZE;
 
 	if (len > high_limit)