[POWERPC] Fix bogus BUG_ON() in in hugetlb_get_unmapped_area()

The powerpc specific version of hugetlb_get_unmapped_area() makes some
unwarranted assumptions about what checks have been made to its
parameters by its callers.  This will lead to a BUG_ON() if a 32-bit
process attempts to make a hugepage mapping which extends above
TASK_SIZE (4GB).

I'm not sure if these assumptions came about because they were valid
with earlier versions of the get_unmapped_area() path, or if it was
always broken.  Nonetheless this patch fixes the logic, and removes
the crash.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/hugetlbpage.c

@@ -744,7 +744,8 @@ static int htlb_check_hinted_area(unsigned long addr, unsigned long len)
 	struct vm_area_struct *vma;
 
 	vma = find_vma(current->mm, addr);
-	if (!vma || ((addr + len) <= vma->vm_start))
+	if (TASK_SIZE - len >= addr &&
+	    (!vma || ((addr + len) <= vma->vm_start)))
 		return 0;
 
 	return -ENOMEM;
@@ -815,6 +816,8 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 		return -EINVAL;
 	if (len & ~HPAGE_MASK)
 		return -EINVAL;
+	if (len > TASK_SIZE)
+		return -ENOMEM;
 
 	if (!cpu_has_feature(CPU_FTR_16M_PAGE))
 		return -EINVAL;
@@ -823,9 +826,6 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	BUG_ON((addr + len)  < addr);
 
 	if (test_thread_flag(TIF_32BIT)) {
-		/* Paranoia, caller should have dealt with this */
-		BUG_ON((addr + len) > 0x100000000UL);
-
 		curareas = current->mm->context.low_htlb_areas;
 
 		/* First see if we can use the hint address */