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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 464BAC433EF for ; Sat, 18 Sep 2021 11:41:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23CBF61244 for ; Sat, 18 Sep 2021 11:41:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235874AbhIRLlW (ORCPT ); Sat, 18 Sep 2021 07:41:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:33662 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229793AbhIRLlU (ORCPT ); Sat, 18 Sep 2021 07:41:20 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 95D1B61244; Sat, 18 Sep 2021 11:39:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631965196; bh=BzRo8ApXY7trnCJ4YSP1u1W1GLdyywjRf4lzNkQ9II0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Rk5GtKtSkrKOa37Armo/WbiMF40SMYf8Z/yR7wQLJ4tq9WvlEnBIZRkh/v7avyV+1 F3jWBZaBjcyK3s4MIFrizkLVTv3itkj4orR1Mq67lK2PEa9dn09GJS3+kyQJ5Ek1k0 jDipUzBhNz72d8ZC/6axWHaQV/QZJgpAOpSiGdC+SlkNm4f/n/D8CKTX2p15oT2QM2 0TAsWlAbZWDnB4N4h513W1swEMpj+nQs7sW0PNjH5scL+6KIqqW+Tn+1ZyL6RhO3OQ UcZfnBAVhOCmMQjNufRvsycfCDXV/v2wltAP2a8387XaTVOCoMThTvANyB2vffLdSt dxUydgSy7D22Q== Date: Sat, 18 Sep 2021 14:39:49 +0300 From: Mike Rapoport To: Christoph Hellwig Cc: Catalin Marinas , 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 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. Otherwise the simplest way would be to hide it behind something like ARCH_WANTS_DMA_NOT_RAM and make arm/arm64 select it. Thoughts? -- Sincerely yours, Mike.