[PATCH 12/16] parisc: 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/parisc/include/uapi/asm/mman.h       | 1 +
 arch/parisc/kernel/sys_parisc.c           | 9 +++++++++
 tools/arch/parisc/include/uapi/asm/mman.h | 1 +
 3 files changed, 11 insertions(+)

diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index 68c44f99bc93..44925ef8ac44 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -26,6 +26,7 @@
 #define MAP_HUGETLB	0x80000		/* create a huge page mapping */
 #define MAP_FIXED_NOREPLACE 0x100000	/* MAP_FIXED which doesn't unmap underlying mapping */
 #define MAP_UNINITIALIZED 0		/* uninitialized anonymous mmap */
+#define MAP_BELOW_HINT  0x200000	/* give out address that is below (inclusive) hint address */
 
 #define MS_SYNC		1		/* synchronous memory sync */
 #define MS_ASYNC	2		/* sync memory asynchronously */
diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
index f7722451276e..feccb60cf746 100644
--- a/arch/parisc/kernel/sys_parisc.c
+++ b/arch/parisc/kernel/sys_parisc.c
@@ -148,6 +148,13 @@ 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(info.high_limit,
+					      (addr + len) - (STACK_TOP - mm->mmap_base));
 		addr = vm_unmapped_area(&info);
 		if (!(addr & ~PAGE_MASK))
 			return addr;
@@ -163,6 +170,8 @@ static unsigned long arch_get_unmapped_area_common(struct file *filp,
 
 	info.low_limit = mm->mmap_base;
 	info.high_limit = mmap_upper_limit(NULL);
+	if (flags & MAP_BELOW_HINT)
+		info.high_limit = MIN(info.high_limit, addr + len);
 	return vm_unmapped_area(&info);
 }
 
diff --git a/tools/arch/parisc/include/uapi/asm/mman.h b/tools/arch/parisc/include/uapi/asm/mman.h
index 4cc88a642e10..297acc0f7b2a 100644
--- a/tools/arch/parisc/include/uapi/asm/mman.h
+++ b/tools/arch/parisc/include/uapi/asm/mman.h
@@ -40,4 +40,5 @@
 /* MAP_32BIT is undefined on parisc, fix it for perf */
 #define MAP_32BIT	0
 #define MAP_UNINITIALIZED	0
+#define MAP_BELOW_MAP	0x200000
 #endif

-- 
2.45.0