amd64: get rid of zeroing

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/lib/usercopy.c

@@ -76,10 +76,11 @@ EXPORT_SYMBOL(_copy_to_user);
  */
 unsigned long _copy_from_user(void *to, const void __user *from, unsigned n)
 {
+	unsigned long res = n;
 	if (access_ok(VERIFY_READ, from, n))
-		n = __copy_from_user(to, from, n);
-	else
-		memset(to, 0, n);
-	return n;
+		res = __copy_from_user_inatomic(to, from, n);
+	if (unlikely(res))
+		memset(to + n - res, 0, res);
+	return res;
 }
 EXPORT_SYMBOL(_copy_from_user);

arch/x86/lib/usercopy_64.c

@@ -80,9 +80,5 @@ copy_user_handle_tail(char *to, char *from, unsigned len)
 			break;
 	}
 	clac();
-
-	/* If the destination is a kernel buffer, we always clear the end */
-	if (!__addr_ok(to))
-		memset(to, 0, len);
 	return len;
 }