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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 98E1BC433E0 for ; Tue, 9 Feb 2021 15:51:10 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C94EA64E27 for ; Tue, 9 Feb 2021 15:51:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C94EA64E27 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id 883C86F56F for ; Tue, 9 Feb 2021 15:51:09 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id kTA-SvVKT3rF for ; Tue, 9 Feb 2021 15:51:08 +0000 (UTC) Received: by smtp3.osuosl.org (Postfix, from userid 1001) id 7ADC36F556; Tue, 9 Feb 2021 15:51:08 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp3.osuosl.org (Postfix) with ESMTP id 5E9396F500; Tue, 9 Feb 2021 15:51:05 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 340CEC0891; Tue, 9 Feb 2021 15:51:05 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id 38930C013A for ; Tue, 9 Feb 2021 15:51:04 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 27B6687171 for ; Tue, 9 Feb 2021 15:51:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tqcIiPRtkBqB for ; Tue, 9 Feb 2021 15:51:02 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by hemlock.osuosl.org (Postfix) with ESMTPS id C274887135 for ; Tue, 9 Feb 2021 15:51:02 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 9E5D467373; Tue, 9 Feb 2021 16:50:58 +0100 (CET) Date: Tue, 9 Feb 2021 16:50:58 +0100 From: Christoph Hellwig To: Robin Murphy Subject: Re: DMA direct mapping fix for 5.4 and earlier stable branches Message-ID: <20210209155058.GA8912@lst.de> References: <27bbe35deacb4ca49f31307f4ed551b5@SOC-EX02V.e01.socionext.com> <20210209093642.GA1006@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Sumit Garg , Daniel Thompson , Greg KH , obayashi.yoshimasa@socionext.com, stable , Linux Kernel Mailing List , iommu@lists.linux-foundation.org, Christoph Hellwig X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Tue, Feb 09, 2021 at 12:45:11PM +0000, Robin Murphy wrote: > It's not a bug, it's a fundamental design failure. dma_get_sgtable() has > only ever sort-of-worked for DMA buffers that come from CMA or regular page > allocations. In particular, a "no-map" DMA pool is not backed by kernel > memory, so does not have any corresponding page structs, so it's impossible > to generate a *valid* scatterlist to represent memory from that pool, > regardless of what you might get away with provided you don't poke too hard > at it. > > It is not a good API... Yes, I don't think anyone should add new users of the API. That being said the commit he is trying to backport fixes a bug in the implementation that at least in theory could also affect in-tree drivers. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu 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=-5.3 required=3.0 tests=BAYES_00, 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 1CAA8C433DB for ; Tue, 9 Feb 2021 15:52:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC9BD64E70 for ; Tue, 9 Feb 2021 15:52:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232627AbhBIPvr (ORCPT ); Tue, 9 Feb 2021 10:51:47 -0500 Received: from verein.lst.de ([213.95.11.211]:47186 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232384AbhBIPvm (ORCPT ); Tue, 9 Feb 2021 10:51:42 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 9E5D467373; Tue, 9 Feb 2021 16:50:58 +0100 (CET) Date: Tue, 9 Feb 2021 16:50:58 +0100 From: Christoph Hellwig To: Robin Murphy Cc: Sumit Garg , Christoph Hellwig , Greg KH , obayashi.yoshimasa@socionext.com, m.szyprowski@samsung.com, iommu@lists.linux-foundation.org, Linux Kernel Mailing List , stable , Daniel Thompson Subject: Re: DMA direct mapping fix for 5.4 and earlier stable branches Message-ID: <20210209155058.GA8912@lst.de> References: <27bbe35deacb4ca49f31307f4ed551b5@SOC-EX02V.e01.socionext.com> <20210209093642.GA1006@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 09, 2021 at 12:45:11PM +0000, Robin Murphy wrote: > It's not a bug, it's a fundamental design failure. dma_get_sgtable() has > only ever sort-of-worked for DMA buffers that come from CMA or regular page > allocations. In particular, a "no-map" DMA pool is not backed by kernel > memory, so does not have any corresponding page structs, so it's impossible > to generate a *valid* scatterlist to represent memory from that pool, > regardless of what you might get away with provided you don't poke too hard > at it. > > It is not a good API... Yes, I don't think anyone should add new users of the API. That being said the commit he is trying to backport fixes a bug in the implementation that at least in theory could also affect in-tree drivers.