From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id E64016B06CB for ; Thu, 3 Aug 2017 10:47:51 -0400 (EDT) Received: by mail-qt0-f197.google.com with SMTP id p48so7072361qtf.1 for ; Thu, 03 Aug 2017 07:47:51 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id p22si30260680qte.548.2017.08.03.07.47.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Aug 2017 07:47:50 -0700 (PDT) Date: Thu, 3 Aug 2017 10:47:46 -0400 From: Jerome Glisse Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator Message-ID: <20170803144746.GA9501@redhat.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170803135549.GW12521@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Igor Stoppa , Linux-MM , LKML , linux-security-module@vger.kernel.org, "kernel-hardening@lists.openwall.com" , Kees Cook On Thu, Aug 03, 2017 at 03:55:50PM +0200, Michal Hocko wrote: > On Thu 03-08-17 15:20:31, Igor Stoppa wrote: > > On 03/08/17 14:48, Michal Hocko wrote: > > > On Thu 03-08-17 13:11:45, Igor Stoppa wrote: > > >> On 02/08/17 20:08, Jerome Glisse wrote: > > >>> On Wed, Aug 02, 2017 at 06:14:28PM +0300, Igor Stoppa wrote: > > > > [...] > > > > >>>> from include/linux/mm_types.h: > > >>>> > > >>>> struct page { > > >>>> ... > > >>>> union { > > >>>> unsigned long private; /* Mapping-private opaque data: > > >>>> * usually used for buffer_heads > > >>>> * if PagePrivate set; used for > > >>>> * swp_entry_t if PageSwapCache; > > >>>> * indicates order in the buddy > > >>>> * system if PG_buddy is set. > > >>>> */ > > > > [...] > > > > >> If the "Mapping-private" was dropped or somehow connected exclusively to > > >> the cases listed in the comment, then I think it would be more clear > > >> that the comment needs to be intended as related to mapping in certain > > >> cases only. > > >> But it is otherwise ok to use the "private" field for whatever purpose > > >> it might be suitable, as long as it is not already in use. > > > > > > I would recommend adding a new field into the enum... > > > > s/enum/union/ ? > > > > If not, I am not sure what is the enum that you are talking about. > > yeah, fat fingers on my side > > > > > [...] > > > > >> But, to reply more specifically to your advice, yes, I think I could add > > >> a flag to vm_struct and then retrieve its value, for the address being > > >> processed, by passing through find_vm_area(). > > > > > > ... and you can store vm_struct pointer to the struct page there > > > > "there" as in the new field of the union? > > btw, what would be a meaningful name, since "private" is already taken? > > > > For simplicity, I'll use, for now, "private2" > > why not explicit vm_area? > > > > and you> won't need to do the slow find_vm_area. I haven't checked > > very closely > > > but this should be possible in principle. I guess other callers might > > > benefit from this as well. > > > > 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. Jerome -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org