On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote:

quoted

-		return 0;
-	return (size == 0 || size - 1 <= seg.seg - addr);
+	if (addr >= TASK_SIZE_MAX)
+		return false;
+	if (size == 0)
+		return false;

__access_ok() was returning true when size == 0 up to now. Any reason to 
return false now ?

No, this is accidental and broken.  Can you re-run your benchmark with
this fixed?