powerpc/mm/hash: Handle mmap_min_addr correctly in get_unmapped_area topdown search

When doing top-down search the low_limit is not PAGE_SIZE but rather
max(PAGE_SIZE, mmap_min_addr). This handle cases in which mmap_min_addr >
PAGE_SIZE.

Fixes: fba2369e6c ("mm: use vm_unmapped_area() on powerpc architecture")
Reviewed-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/slice.c

@@ -32,6 +32,7 @@
 #include <linux/export.h>
 #include <linux/hugetlb.h>
 #include <linux/sched/mm.h>
+#include <linux/security.h>
 #include <asm/mman.h>
 #include <asm/mmu.h>
 #include <asm/copro.h>
@@ -377,6 +378,7 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 	int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
 	unsigned long addr, found, prev;
 	struct vm_unmapped_area_info info;
+	unsigned long min_addr = max(PAGE_SIZE, mmap_min_addr);
 
 	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 	info.length = len;
@@ -393,7 +395,7 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 	if (high_limit > DEFAULT_MAP_WINDOW)
 		addr += mm->context.slb_addr_limit - DEFAULT_MAP_WINDOW;
 
-	while (addr > PAGE_SIZE) {
+	while (addr > min_addr) {
 		info.high_limit = addr;
 		if (!slice_scan_available(addr - 1, available, 0, &addr))
 			continue;
@@ -405,8 +407,8 @@ static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 		 * Check if we need to reduce the range, or if we can
 		 * extend it to cover the previous available slice.
 		 */
-		if (addr < PAGE_SIZE)
+		if (addr < min_addr)
-			addr = PAGE_SIZE;
+			addr = min_addr;
 		else if (slice_scan_available(addr - 1, available, 0, &prev)) {
 			addr = prev;
 			goto prev_slice;
@@ -528,7 +530,7 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 		addr = _ALIGN_UP(addr, page_size);
 		slice_dbg(" aligned addr=%lx\n", addr);
 		/* Ignore hint if it's too large or overlaps a VMA */
-		if (addr > high_limit - len ||
+		if (addr > high_limit - len || addr < mmap_min_addr ||
 		    !slice_area_is_free(mm, addr, len))
 			addr = 0;
 	}