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=-2.2 required=3.0 tests=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 421A5C43331 for ; Thu, 26 Mar 2020 17:05:27 +0000 (UTC) Received: from silver.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 1E9B52076A for ; Thu, 26 Mar 2020 17:05:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1E9B52076A 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 silver.osuosl.org (Postfix) with ESMTP id EB9D226291; Thu, 26 Mar 2020 17:05:26 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JMNjkgBRvjhZ; Thu, 26 Mar 2020 17:05:24 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 8C06C2153D; Thu, 26 Mar 2020 17:05:24 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 7F47EC1D7C; Thu, 26 Mar 2020 17:05:24 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id E0804C0177 for ; Thu, 26 Mar 2020 17:05:22 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id CB0B988587 for ; Thu, 26 Mar 2020 17:05:22 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9T61-2FFW5s7 for ; Thu, 26 Mar 2020 17:05:21 +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 whitealder.osuosl.org (Postfix) with ESMTPS id 4E7A78857E for ; Thu, 26 Mar 2020 17:05:21 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id CF3D2227A81; Thu, 26 Mar 2020 18:05:16 +0100 (CET) Date: Thu, 26 Mar 2020 18:05:16 +0100 From: Christoph Hellwig To: Alexander Graf Subject: Re: [PATCH] swiotlb: Allow swiotlb to live at pre-defined address Message-ID: <20200326170516.GB6387@lst.de> References: <20200326162922.27085-1-graf@amazon.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200326162922.27085-1-graf@amazon.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: Mark Rutland , benh@amazon.com, Konrad Rzeszutek Wilk , Jan Kiszka , x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, aggh@amazon.com, alcioa@amazon.com, iommu@lists.linux-foundation.org, aagch@amazon.com, dhr@amazon.com, dwmw@amazon.com, Robin Murphy , 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 Thu, Mar 26, 2020 at 05:29:22PM +0100, Alexander Graf wrote: > The swiotlb is a very convenient fallback mechanism for bounce buffering of > DMAable data. It is usually used for the compatibility case where devices > can only DMA to a "low region". > > However, in some scenarios this "low region" may be bound even more > heavily. For example, there are embedded system where only an SRAM region > is shared between device and CPU. There are also heterogeneous computing > scenarios where only a subset of RAM is cache coherent between the > components of the system. There are partitioning hypervisors, where > a "control VM" that implements device emulation has limited view into a > partition's memory for DMA capabilities due to safety concerns. > > This patch adds a command line driven mechanism to move all DMA memory into > a predefined shared memory region which may or may not be part of the > physical address layout of the Operating System. > > Ideally, the typical path to set this configuration would be through Device > Tree or ACPI, but neither of the two mechanisms is standardized yet. Also, > in the x86 MicroVM use case, we have neither ACPI nor Device Tree, but > instead configure the system purely through kernel command line options. > > I'm sure other people will find the functionality useful going forward > though and extend it to be triggered by DT/ACPI in the future. I'm totally against hacking in a kernel parameter for this. We'll need a proper documented DT or ACPI way. We also need to feed this information into the actual DMA bounce buffering decisions and not just the swiotlb placement. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu