From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754808AbbLINzs (ORCPT <rfc822;w@1wt.eu>);
	Wed, 9 Dec 2015 08:55:48 -0500
Received: from mail-wm0-f51.google.com ([74.125.82.51]:35149 "EHLO
	mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753218AbbLINzq (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 9 Dec 2015 08:55:46 -0500
Date: Wed, 9 Dec 2015 14:55:44 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Sebastian Frias <sebastian_frias@sigmadesigns.com>
Cc: linux-mm@kvack.org, Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
        linux-kernel@vger.kernel.org
Subject: Re: m(un)map kmalloc buffers to userspace
Message-ID: <20151209135544.GE30907@dhcp22.suse.cz>
References: <5667128B.3080704@sigmadesigns.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5667128B.3080704@sigmadesigns.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue 08-12-15 18:25:31, Sebastian Frias wrote:
> Hi,
> 
> We are porting a driver from Linux 3.4.39+ to 4.1.13+, CPU is Cortex-A9.
> 
> The driver maps kmalloc'ed memory to user space.

This sounds like a terrible idea to me. Why don't you simply use the
page allocator directly? Try to imagine what would happen if you mmaped
a kmalloc with a size which is not page aligned? mmaped memory uses
whole page granularity.
-- 
Michal Hocko
SUSE Labs