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, URIBL_BLOCKED,USER_AGENT_SANE_2 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 DF71BC433ED for ; Thu, 13 May 2021 23:38:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A2ADC610A7 for ; Thu, 13 May 2021 23:38:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230210AbhEMXjP (ORCPT ); Thu, 13 May 2021 19:39:15 -0400 Received: from mga05.intel.com ([192.55.52.43]:7286 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230230AbhEMXjN (ORCPT ); Thu, 13 May 2021 19:39:13 -0400 IronPort-SDR: 2YkOzYHz9Cqk9R8JUmje4f42+hbByX3/KJtOwl2+71O8GkCNYlnoy61RDA6at3lYMWQXctfDOj 8VYMmDvCXy9A== X-IronPort-AV: E=McAfee;i="6200,9189,9983"; a="285592759" X-IronPort-AV: E=Sophos;i="5.82,296,1613462400"; d="scan'208";a="285592759" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2021 16:38:02 -0700 IronPort-SDR: LSmIhSZ/iJ19HTFkyX5tBW+4f5BeEKik1AweyzWqWzo8Zjwf1GY38yktThsKCjhW+YTcFICCZA 6tvEi3QdOioA== X-IronPort-AV: E=Sophos;i="5.82,296,1613462400"; d="scan'208";a="392484089" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2021 16:38:02 -0700 Date: Thu, 13 May 2021 16:40:28 -0700 From: Jacob Pan To: Jason Gunthorpe Cc: "Luck, Tony" , Christoph Hellwig , LKML , "iommu@lists.linux-foundation.org" , Joerg Roedel , Lu Baolu , Jean-Philippe Brucker , "Liu, Yi L" , "Raj, Ashok" , "Tian, Kevin" , "Jiang, Dave" , "wangzhou1@hisilicon.com" , "zhangfei.gao@linaro.org" , "vkoul@kernel.org" , David Woodhouse , jacob.jun.pan@linux.intel.com Subject: Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags Message-ID: <20210513164028.6e2d6e59@jacob-builder> In-Reply-To: <20210513223122.GV1002214@nvidia.com> References: <20210513081050.5cf6a6ed@jacob-builder> <20210513173303.GL1002214@nvidia.com> <20210513185349.GA801495@agluck-desk2.amr.corp.intel.com> <20210513190040.GR1002214@nvidia.com> <20210513192014.GU1002214@nvidia.com> <20210513124621.01421173@jacob-builder> <20210513195749.GA801830@agluck-desk2.amr.corp.intel.com> <20210513132251.0ff89b90@jacob-builder> <20210513223122.GV1002214@nvidia.com> Organization: OTC X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Jason, On Thu, 13 May 2021 19:31:22 -0300, Jason Gunthorpe wrote: > On Thu, May 13, 2021 at 01:22:51PM -0700, Jacob Pan wrote: > > Hi Tony, > > > > On Thu, 13 May 2021 12:57:49 -0700, "Luck, Tony" > > wrote: > > > > > On Thu, May 13, 2021 at 12:46:21PM -0700, Jacob Pan wrote: > > > > It seems there are two options: > > > > 1. Add a new IOMMU API to set up a system PASID with a *separate* > > > > IOMMU page table/domain, mark the device is PASID only with a flag. > > > > Use DMA APIs to explicit map/unmap. Based on this PASID-only flag, > > > > Vendor IOMMU driver will decide whether to use system PASID domain > > > > during map/unmap. Not clear if we also need to make IOVA==kernel VA. > > > > > > > > 2. Add a new IOMMU API to setup a system PASID which points to > > > > init_mm.pgd. This API only allows trusted device to bind with the > > > > system PASID at its own risk. There is no need for DMA API. This is > > > > the same as the current code except with an explicit API. > > > > > > > > Which option? > > > > > > Option #1 looks cleaner to me. Option #2 gives access to bits > > > of memory that the users of system PASID shouldn't ever need > > > to touch ... just map regions of memory that the kernel has > > > a "struct page" for. > > > > > > What does "use DMA APIs to explicitly map/unmap" mean? Is that > > > for the whole region? > > > > > If we map the entire kernel direct map during system PASID setup, then > > we don't need to use DMA API to map/unmap certain range. > > > > I was thinking this system PASID page table could be on-demand. The > > mapping is built by explicit use of DMA map/unmap APIs. > > Option 1 should be the PASID works exactly like a normal RID and uses > all the normal DMA APIs and IOMMU mechanisms, whatever the platform > implements. This might mean an iommu update on every operation or not. > > > > I'm expecting that once this system PASID has been initialized, > > > then any accelerator device with a kernel use case would use the > > > same PASID. I.e. DSA for page clearing, IAX for ZSwap compression > > > & decompression, etc. > > > > > OK, sounds like we have to map the entire kernel VA with struct page as > > you said. So we still by-pass DMA APIs, can we all agree on that? > > Option 2 should be the faster option, but not available in all cases. > > Option 1 isn't optional. DMA and IOMMU code has to be portable and > this is the portable API. > > If you want to do option 1 and option 2 then give it a go, but in most > common cases with the IOMMU in a direct map you shouldn't get a > notable performance win. > Looks like we are converging. Let me summarize the takeaways: 1. Remove IOMMU_SVA_BIND_SUPERVISOR flag from this patch, in fact there will be no flags at all for iommu_sva_bind_device() 2. Remove all supervisor SVA related vt-d, idxd code. 3. Create API iommu_setup_system_pasid_direct_map(option_flag) if (option_flag == 1) iommu_domain_alloc(IOMMU_DOMAIN_DMA); if (option_flag == 2) iommu_domain_alloc(IOMMU_DOMAIN_DIRECT); //new domain type? setup IOMMU page tables mirroring the direct map 4. Create API iommu_enable_dev_direct_map(struct dev, &pasid, &option) - Drivers call this API to get the system PASID and which option is available on the system PASID - mark device as PASID only, perhaps a new flag in struct device->dev_iommu->pasid_only = 1 5. DMA API IOMMU vendor ops will take action based on the pasid_only flag to decide if the mapping is for system PASID page tables. Does it make sense? > Jason Thanks, Jacob