From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752148AbeDETQ5 (ORCPT ); Thu, 5 Apr 2018 15:16:57 -0400 Received: from mail-pl0-f51.google.com ([209.85.160.51]:43467 "EHLO mail-pl0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752023AbeDETQy (ORCPT ); Thu, 5 Apr 2018 15:16:54 -0400 X-Google-Smtp-Source: AIpwx4/VZnfApXSfVxcpSI2FLpPNBt7uOAL8T8XAd5/XwicBza6xA7U8bp5Lu/IIyEJwtO7fDB/6jg== Subject: Re: [PATCH v7 2/5] of: change overlay apply input data from unflattened to FDT To: Jan Kiszka , Rob Herring Cc: Pantelis Antoniou , Pantelis Antoniou , devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" , Geert Uytterhoeven , Laurent Pinchart , Jailhouse , Frank Rowand References: <1520122673-11003-1-git-send-email-frowand.list@gmail.com> <1520122673-11003-3-git-send-email-frowand.list@gmail.com> <09e3db63-cbf9-52a2-ee77-520979f17fea@web.de> <935d6135-c5db-e5f8-b850-8ef26ce0c0a0@web.de> From: Frank Rowand Message-ID: <69c06530-94df-b67b-4e56-6519275afb45@gmail.com> Date: Thu, 5 Apr 2018 12:16:52 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <935d6135-c5db-e5f8-b850-8ef26ce0c0a0@web.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/05/18 00:22, Jan Kiszka wrote: > On 2018-04-05 02:55, Rob Herring wrote: >> On Wed, Apr 4, 2018 at 5:35 PM, Jan Kiszka wrote: >>> Hi Frank, >>> >>> On 2018-03-04 01:17, frowand.list@gmail.com wrote: >>>> From: Frank Rowand >>>> >>>> Move duplicating and unflattening of an overlay flattened devicetree >>>> (FDT) into the overlay application code. To accomplish this, >>>> of_overlay_apply() is replaced by of_overlay_fdt_apply(). >>>> >>>> The copy of the FDT (aka "duplicate FDT") now belongs to devicetree >>>> code, which is thus responsible for freeing the duplicate FDT. The >>>> caller of of_overlay_fdt_apply() remains responsible for freeing the >>>> original FDT. >>>> >>>> The unflattened devicetree now belongs to devicetree code, which is >>>> thus responsible for freeing the unflattened devicetree. >>>> >>>> These ownership changes prevent early freeing of the duplicated FDT >>>> or the unflattened devicetree, which could result in use after free >>>> errors. >>>> >>>> of_overlay_fdt_apply() is a private function for the anticipated >>>> overlay loader. >>> >>> We are using of_fdt_unflatten_tree + of_overlay_apply in the >>> (out-of-tree) Jailhouse loader driver in order to register a virtual >>> device during hypervisor activation with Linux. The DT overlay is >>> created from a a template but modified prior to application to account >>> for runtime-specific parameters. See [1] for the current implementation. >>> >>> I'm now wondering how to model that scenario best with the new API. >>> Given that the loader lost ownership of the unflattened tree but the >>> modification API exist only for the that DT state, I'm not yet seeing a >>> clear solution. Should we apply the template in disabled form (status = >>> "disabled"), modify it, and then activate it while it is already applied? >> >> No. I don't think that will work. >> >> The of_overlay_apply() function is still there, but static. We can >> export it again if the need arises. > > That would be the simplest solution from our perspective, but I'm not > sure if that is in the original spirit of this change. For short term out of tree usage, exporting of_overlay_apply() is ok. Yes, for in-tree, exporting it again defeats the attempted process to solve the overlay issues to make them acceptable in main line. >> >> Another option is there is a notifier callback OF_OVERLAY_PRE_APPLY, >> but I'm not sure we want to make that be the normal interface to make >> modifications. > > And would calling modification functions from that callback be legal at all? It might work in some specific cases, but the result is undefined. > > Jan >