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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 0D931C28CC6 for ; Mon, 3 Jun 2019 10:52:06 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 E3CAF280D2 for ; Mon, 3 Jun 2019 10:52:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3CAF280D2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id AF4C2C6A; Mon, 3 Jun 2019 10:52:05 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id D3BBDBE4 for ; Mon, 3 Jun 2019 10:52:03 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id A50305D3 for ; Mon, 3 Jun 2019 10:52:02 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id C6EF836B; Mon, 3 Jun 2019 12:51:59 +0200 (CEST) Date: Mon, 3 Jun 2019 12:51:58 +0200 From: Joerg Roedel To: Tom Murphy Subject: Re: [PATCH v3 0/4] iommu/amd: Convert the AMD iommu driver to the dma-iommu api Message-ID: <20190603105158.GL12745@8bytes.org> References: <20190506185207.31069-1-tmurphy@arista.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190506185207.31069-1-tmurphy@arista.com> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: Heiko Stuebner , Will Deacon , David Brown , Thierry Reding , linux-s390@vger.kernel.org, linux-samsung-soc@vger.kernel.org, iommu@lists.linux-foundation.org, Krzysztof Kozlowski , Jonathan Hunter , linux-rockchip@lists.infradead.org, Kukjin Kim , Gerald Schaefer , Andy Gross , linux-tegra@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mediatek@lists.infradead.org, Matthias Brugger , linux-arm-kernel@lists.infradead.org, Robin Murphy , linux-kernel@vger.kernel.org, murphyt7@tcd.ie, David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 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 Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org Hi Tom, On Mon, May 06, 2019 at 07:52:02PM +0100, Tom Murphy wrote: > Convert the AMD iommu driver to the dma-iommu api. Remove the iova > handling and reserve region code from the AMD iommu driver. Thank you for your work on this! I appreciate that much, but I am not sure we are ready to make that move for the AMD and Intel IOMMU drivers yet. My main concern right now is that these changes will add a per-page table lock into the fast-path for dma-mapping operations. There has been much work in the past to remove all locking from these code-paths and make it scalable on x86. The dma-ops implementations in the x86 IOMMU drivers have the benefit that they can call their page-table manipulation functions directly and without locks, because they can make the necessary assumptions. The IOMMU-API mapping/unmapping path can't make these assumptions because it is also used for non-DMA-API use-cases. So before we can move the AMD and Intel drivers to the generic DMA-API implementation we need to solve this problem to not introduce new scalability regressions. Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu