[PATCH 10/16] arm: mm: Support MAP_BELOW_HINT

Charlie Jenkins
2024-08-28T05:50:19Z

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@rivosinc.com>
---
arch/arm/mm/mmap.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index d65d0e6ed10a..fa0c79447b78 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -71,6 +71,8 @@ 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 = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
info.align_offset = pgoff << PAGE_SHIFT;
return vm_unmapped_area(&info);
@@ -122,6 +124,12 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
info.length = len;
info.low_limit = FIRST_USER_ADDRESS;
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 = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
info.align_offset = pgoff << PAGE_SHIFT;
addr = vm_unmapped_area(&info);
@@ -137,6 +145,8 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
info.flags = 0;
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);
addr = vm_unmapped_area(&info);
}

--
2.45.0