[PATCH 09/16] loongarch: mm: Support MAP_BELOW_HINT

[Charlie Jenkins]

Add support for MAP_BELOW_HINT to mmap by restricting high_limit to addr
when the flag is enabled.

Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>
---
 arch/loongarch/mm/mmap.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/loongarch/mm/mmap.c b/arch/loongarch/mm/mmap.c
index 889030985135..66a5badf849b 100644
--- a/arch/loongarch/mm/mmap.c
+++ b/arch/loongarch/mm/mmap.c
@@ -70,6 +70,13 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
 		info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 		info.low_limit = PAGE_SIZE;
 		info.high_limit = mm->mmap_base;
+		if (flags & MAP_BELOW_HINT)
+			/*
+			 * Subtract (STACK_TOP - mm->mmap_base) to get random
+			 * offset defined in mmap_base() in mm/util.c
+			 */
+			info.high_limit = MIN(mm->mmap_base,
+					      (addr + len) - (STACK_TOP - mm->mmap_base))
 		addr = vm_unmapped_area(&info);
 
 		if (!(addr & ~PAGE_MASK))
@@ -84,7 +91,11 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
 	}
 
 	info.low_limit = mm->mmap_base;
+
 	info.high_limit = TASK_SIZE;
+	if (flags & MAP_BELOW_HINT)
+		info.high_limit = MIN(info.high_limit, addr + len);
+
 	return vm_unmapped_area(&info);
 }
 

-- 
2.45.0