From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24941C433FE for ; Thu, 10 Nov 2022 01:54:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232213AbiKJByd (ORCPT ); Wed, 9 Nov 2022 20:54:33 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49996 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232038AbiKJBy3 (ORCPT ); Wed, 9 Nov 2022 20:54:29 -0500 Received: from fudo.makrotopia.org (fudo.makrotopia.org [IPv6:2a07:2ec0:3002::71]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 198A4C771; Wed, 9 Nov 2022 17:54:27 -0800 (PST) Received: from local by fudo.makrotopia.org with esmtpsa (TLS1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.94.2) (envelope-from ) id 1oswlW-0002Yx-Jg; Thu, 10 Nov 2022 02:54:02 +0100 Date: Thu, 10 Nov 2022 01:52:43 +0000 From: Daniel Golle To: Matthew Wilcox Cc: Jens Axboe , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Davidlohr Bueso , "Martin K. Petersen" , Chaitanya Kulkarni , Ming Lei , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-efi@vger.kernel.org Subject: Re: [PATCH v4 2/5] block: add partition parser for U-Boot uImage.FIT Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Wed, Nov 09, 2022 at 05:21:01PM +0000, Matthew Wilcox wrote: > On Wed, Nov 09, 2022 at 02:36:11PM +0000, Daniel Golle wrote: > > On Wed, Nov 09, 2022 at 01:58:29PM +0000, Matthew Wilcox wrote: > > > ... actually, why can't you call read_part_sector() and avoid all of > > > this? > > > > I've tried that before and the problem is that read_part_sector() > > returns a pointer to one sector (typically 512 bytes) of data. > > And this pointer should not be accesses beyond sector boundaries, > > right? You'd have to call read_part_sector() again for the next > > sector. > > > > The FIT structure, however, usually exceeds the size of one sector, > > and having a continous memory area covering the structure as a whole > > is crucial for libfdt to do its job. > > > > I could, of course, use read_part_sector() to copy all sectors > > covering the FIT structure into a buffer, but that seemed strange > > given that read_part_sector() actually used read_mapping_page() > > (and now uses read_mapping_folio()) internally and then returns a > > pointer to the offset within the page/folio. So why not read it in one > > piece in first place instead of having it first split up to sectors > > by read_part_sector() just to then having to reassemble it into a > > continous buffer again. > > Are you guaranteed that it's "sufficiently" aligned on storage so > that it fits entirely within a single page? If not, you'll have > to copy it, vmap it, or fix libfdt to handle a segmented buffer. Yes, for the uImage.FIT to be usable for the partition parser it has to be page-aligned. There is a check which makes sure that this is the case: > + /* uImage.FIT should be aligned to page boundaries */ > + if (fit_start_sector % (1 << (PAGE_SHIFT - SECTOR_SHIFT))) > + return 0; In case of mtdblock or ubiblock devices, the image always starts at offset 0, so this is never a problem. In case of the image being stored in a GPT partition, one has to make sure that the start sector of the partition is page aligned, otherwise the above check will fail and the partition parser will bail out.