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,USER_AGENT_MUTT autolearn=unavailable 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 37EB4C04AB5 for ; Mon, 3 Jun 2019 10:52:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B216280D2 for ; Mon, 3 Jun 2019 10:52:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727565AbfFCKwB (ORCPT ); Mon, 3 Jun 2019 06:52:01 -0400 Received: from 8bytes.org ([81.169.241.247]:41064 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727255AbfFCKwB (ORCPT ); Mon, 3 Jun 2019 06:52:01 -0400 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 Cc: iommu@lists.linux-foundation.org, murphyt7@tcd.ie, Will Deacon , Robin Murphy , Marek Szyprowski , Kukjin Kim , Krzysztof Kozlowski , David Woodhouse , Andy Gross , David Brown , Matthias Brugger , Rob Clark , Heiko Stuebner , Gerald Schaefer , Thierry Reding , Jonathan Hunter , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-s390@vger.kernel.org, linux-tegra@vger.kernel.org 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190506185207.31069-1-tmurphy@arista.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.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