From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751662AbdHCPJB (ORCPT ); Thu, 3 Aug 2017 11:09:01 -0400 Received: from lhrrgout.huawei.com ([194.213.3.17]:32617 "EHLO lhrrgout.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751133AbdHCPI7 (ORCPT ); Thu, 3 Aug 2017 11:08:59 -0400 Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator To: Jerome Glisse , Michal Hocko CC: Linux-MM , LKML , , "kernel-hardening@lists.openwall.com" , Kees Cook References: <07063abd-2f5d-20d9-a182-8ae9ead26c3c@huawei.com> <20170802170848.GA3240@redhat.com> <8e82639c-40db-02ce-096a-d114b0436d3c@huawei.com> <20170803114844.GO12521@dhcp22.suse.cz> <20170803135549.GW12521@dhcp22.suse.cz> <20170803144746.GA9501@redhat.com> From: Igor Stoppa Message-ID: Date: Thu, 3 Aug 2017 18:06:11 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170803144746.GA9501@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.122.225.51] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020206.59833C75.006B,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 5acb2892ebed374a65cb7f75df5c6bb5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/08/17 17:47, Jerome Glisse wrote: > On Thu, Aug 03, 2017 at 03:55:50PM +0200, Michal Hocko wrote: >> On Thu 03-08-17 15:20:31, Igor Stoppa wrote: [...] >>> I am confused about this: if "private2" is a pointer, but when I get an >>> address, I do not even know if the address represents a valid pmalloc >>> page, how can i know when it's ok to dereference "private2"? >> >> because you can make all pages which back vmalloc mappings have vm_area >> pointer set. > > Note that i think this might break some device driver that use vmap() > i think some of them use private field to store device driver specific > informations. But there likely is an unuse field in struct page that > can be use for that. This increases the unease from my side ... it looks like there is no way to fully understand if a field is really used or not, without having deep intimate knowledge of lots of code that is only marginally involved :-/ Similarly, how would I be able to specify what would be the correct way to decide the member of the union to use for handling the field? If there were either some sort of non-multiplexed tag/cookie field or a function, that would specify how to treat the various unions, then it would be easier to multiplex the remaining data, according to how the page is used. -- igor