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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A4661C433F5 for ; Mon, 20 Sep 2021 10:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A7E360F46 for ; Mon, 20 Sep 2021 10:58:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236203AbhITK7h (ORCPT ); Mon, 20 Sep 2021 06:59:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:37294 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229999AbhITK7a (ORCPT ); Mon, 20 Sep 2021 06:59:30 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7885B60F3A; Mon, 20 Sep 2021 10:58:01 +0000 (UTC) Date: Mon, 20 Sep 2021 11:57:58 +0100 From: Catalin Marinas To: Mike Rapoport Cc: Christoph Hellwig , David Hildenbrand , Robin Murphy , Alex Bee , Will Deacon , Andrew Morton , Anshuman Khandual , Linux Kernel Mailing List , linux-mm@kvack.org, Linux ARM Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases) Message-ID: References: <20210824173741.GC623@arm.com> <0908ce39-7e30-91fa-68ef-11620f9596ae@arm.com> <60a11eba-2910-3b5f-ef96-97d4556c1596@redhat.com> <20210825102044.GA3420@arm.com> <20210918051843.GA16104@lst.de> 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-kernel@vger.kernel.org On Sat, Sep 18, 2021 at 02:39:49PM +0300, Mike Rapoport wrote: > On Sat, Sep 18, 2021 at 11:37:22AM +0300, Mike Rapoport wrote: > > On Sat, Sep 18, 2021 at 07:18:43AM +0200, Christoph Hellwig wrote: > > > On Sat, Sep 18, 2021 at 12:22:47AM +0300, Mike Rapoport wrote: > > > > I did some digging and it seems that the most "generic" way to check if a > > > > page is in RAM is page_is_ram(). It's not 100% bullet proof as it'll give > > > > false negatives for architectures that do not register "System RAM", but > > > > those are not using dma_map_resource() anyway and, apparently, never would. > > > > > > The downside of page_is_ram is that it looks really expensiv for > > > something done at dma mapping time. > > > > Indeed :( > > But pfn_valid is plain wrong... > > I'll keep digging. > > I did some more archaeology and it that check for pfn_valid() was requested > by arm folks because their MMU may have troubles with alias mappings with > different attributes and so they made the check to use a false assumption > that pfn_valid() == "RAM". > > As this WARN_ON(pfn_valid()) is only present in dma_map_resource() it's > probably safe to drop it entirely. I agree, we should drop it. IIUC dma_map_resource() does not create any kernel mapping to cause problems with attribute aliasing. You'd need a prior devm_ioremap_resource() if you want access to that range from the CPU side. For arm64 at least, the latter ends up with a pfn_is_map_memory() check. -- Catalin