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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41817C3A59B for ; Fri, 30 Aug 2019 14:59:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 209D923427 for ; Fri, 30 Aug 2019 14:59:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728098AbfH3O7l (ORCPT ); Fri, 30 Aug 2019 10:59:41 -0400 Received: from verein.lst.de ([213.95.11.211]:56266 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727958AbfH3O7j (ORCPT ); Fri, 30 Aug 2019 10:59:39 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 8244E68BFE; Fri, 30 Aug 2019 16:59:35 +0200 (CEST) Date: Fri, 30 Aug 2019 16:59:35 +0200 From: Christoph Hellwig To: Russell King - ARM Linux admin Cc: Christoph Hellwig , iommu@lists.linux-foundation.org, Robin Murphy , linux-arm-kernel@lists.infradead.org, linux-xtensa@linux-xtensa.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code Message-ID: <20190830145935.GA19838@lst.de> References: <20190830062924.21714-1-hch@lst.de> <20190830062924.21714-2-hch@lst.de> <20190830092918.GV13294@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190830092918.GV13294@shell.armlinux.org.uk> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 30, 2019 at 10:29:18AM +0100, Russell King - ARM Linux admin wrote: > On Fri, Aug 30, 2019 at 08:29:21AM +0200, Christoph Hellwig wrote: > > The arm architecture had a VM_ARM_DMA_CONSISTENT flag to mark DMA > > coherent remapping for a while. Lift this flag to common code so > > that we can use it generically. We also check it in the only place > > VM_USERMAP is directly check so that we can entirely replace that > > flag as well (although I'm not even sure why we'd want to allow > > remapping DMA appings, but I'd rather not change behavior). > > Good, because if you did change that behaviour, you'd break almost > every ARM framebuffer and cripple ARM audio drivers. How would that break them? All the usual video and audio drivers that use dma_alloc_* then use dma_mmap_* which never end up in the only place that actually checks VM_USERMAP (remap_vmalloc_range_partial) as they end up in the dma_map_ops mmap methods which contain what is effecitvely open coded versions of that routine. There are very few callers of remap_vmalloc_range_partial / remap_vmalloc_range, and while a few of those actually are in media drivers and the virtual frame buffer video driver, none of these seems to be called on dma memory (which would be a layering violation anyway).