[PATCH 13/16] s390: 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/s390/mm/mmap.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 206756946589..29e20351ca85 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -105,6 +105,8 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.length = len;
 	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);
 	info.align_mask = get_align_mask(filp, flags);
 	info.align_offset = pgoff << PAGE_SHIFT;
 	addr = vm_unmapped_area(&info);
@@ -143,6 +145,12 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long ad
 	info.length = len;
 	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(info.high_limit, addr + len) - (STACK_TOP - mm->mmap_base);
 	info.align_mask = get_align_mask(filp, flags);
 	info.align_offset = pgoff << PAGE_SHIFT;
 	addr = vm_unmapped_area(&info);
@@ -158,6 +166,8 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long ad
 		info.flags = 0;
 		info.low_limit = TASK_UNMAPPED_BASE;
 		info.high_limit = TASK_SIZE;
+		if (flags & MAP_BELOW_HINT)
+			info.high_limit = MIN(TASK_SIZE, addr + len);
 		addr = vm_unmapped_area(&info);
 		if (offset_in_page(addr))
 			return addr;

-- 
2.45.0