powerpc/64s/hash: Fix 512T hint detection to use >= 128T

Currently userspace is able to request mmap() search between 128T-512T
by specifying a hint address that is greater than 128T. But that means
a hint of 128T exactly will return an address below 128T, which is
confusing and wrong.

So fix the logic to check the hint is greater than *or equal* to 128T.

Fixes: f4ea6dcb08 ("powerpc/mm: Enable mappings above 128TB")
Cc: stable@vger.kernel.org # v4.12+
Suggested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Suggested-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Split out of Nick's bigger patch]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/slice.c

@@ -419,7 +419,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	/*
 	 * Check if we need to expland slice area.
 	 */
-	if (unlikely(addr > mm->context.addr_limit &&
+	if (unlikely(addr >= mm->context.addr_limit &&
 		     mm->context.addr_limit != TASK_SIZE)) {
 		mm->context.addr_limit = TASK_SIZE;
 		on_each_cpu(slice_flush_segments, mm, 1);
@@ -427,7 +427,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	/*
 	 * This mmap request can allocate upt to 512TB
 	 */
-	if (addr > DEFAULT_MAP_WINDOW)
+	if (addr >= DEFAULT_MAP_WINDOW)
 		high_limit = mm->context.addr_limit;
 	else
 		high_limit = DEFAULT_MAP_WINDOW;