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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4C2AEC433FE for ; Tue, 7 Dec 2021 01:52:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235439AbhLGB4X (ORCPT ); Mon, 6 Dec 2021 20:56:23 -0500 Received: from mga12.intel.com ([192.55.52.136]:2913 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234802AbhLGB4W (ORCPT ); Mon, 6 Dec 2021 20:56:22 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10190"; a="217481070" X-IronPort-AV: E=Sophos;i="5.87,293,1631602800"; d="scan'208";a="217481070" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Dec 2021 17:52:52 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,293,1631602800"; d="scan'208";a="515038186" Received: from allen-box.sh.intel.com (HELO [10.239.159.118]) ([10.239.159.118]) by orsmga008.jf.intel.com with ESMTP; 06 Dec 2021 17:52:44 -0800 Cc: baolu.lu@linux.intel.com, Greg Kroah-Hartman , Alex Williamson , Bjorn Helgaas , Christoph Hellwig , Kevin Tian , Ashok Raj , Will Deacon , Robin Murphy , Dan Williams , rafael@kernel.org, Diana Craciun , Cornelia Huck , Eric Auger , Liu Yi L , Jacob jun Pan , Chaitanya Kulkarni , Stuart Yoder , Laurentiu Tudor , Thierry Reding , David Airlie , Daniel Vetter , Jonathan Hunter , Li Yang , Dmitry Osipenko , iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 01/18] iommu: Add device dma ownership set/release interfaces To: Jason Gunthorpe , Joerg Roedel References: <20211206015903.88687-1-baolu.lu@linux.intel.com> <20211206015903.88687-2-baolu.lu@linux.intel.com> <20211206150144.GC4670@nvidia.com> From: Lu Baolu Message-ID: Date: Tue, 7 Dec 2021 09:52:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211206150144.GC4670@nvidia.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 12/6/21 11:01 PM, Jason Gunthorpe wrote: > On Mon, Dec 06, 2021 at 02:35:55PM +0100, Joerg Roedel wrote: >> On Mon, Dec 06, 2021 at 09:58:46AM +0800, Lu Baolu wrote: >>> >From the perspective of who is initiating the device to do DMA, device >>> DMA could be divided into the following types: >>> >>> DMA_OWNER_DMA_API: Device DMAs are initiated by a kernel driver >>> through the kernel DMA API. >>> DMA_OWNER_PRIVATE_DOMAIN: Device DMAs are initiated by a kernel >>> driver with its own PRIVATE domain. >>> DMA_OWNER_PRIVATE_DOMAIN_USER: Device DMAs are initiated by >>> userspace. >> >> I have looked at the other iommu patches in this series, but I still >> don't quite get what the difference in the code flow is between >> DMA_OWNER_PRIVATE_DOMAIN and DMA_OWNER_PRIVATE_DOMAIN_USER. What are the >> differences in the iommu core behavior based on this setting? > > USER causes the IOMMU code to spend extra work to never assign the > default domain. Lu, it would be good to update the comment with this > detail > > Once in USER mode the domain is always a /dev/null domain or a domain > controlled by userspace. Never a domain pointing at kernel memory. Yes. The __iommu_detach_group() re-attaches the default domain automatically. This is not allowed once in USER mode. I will update the comments whit this detail. > >>> struct group_device { >>> @@ -621,6 +624,7 @@ struct iommu_group *iommu_group_alloc(void) >>> INIT_LIST_HEAD(&group->devices); >>> INIT_LIST_HEAD(&group->entry); >>> BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier); >>> + group->dma_owner = DMA_OWNER_NONE; >> >> >> DMA_OWNER_NONE is also questionable. All devices are always in one >> domain, and the default domain is always the one used for DMA-API, so >> why isn't the initial value DMA_OWNER_DMA_API? > > 'NONE' means the group is in the default domain but no driver is bound > and thus DMA isn't being used. Seeing NONE is the only condition when > it is OK to change the domain. > > This could be reworked to instead rely on the refcount == 0 as the > signal to know it is OK to change the domain and then we never have > NONE at all. Lu? NONE is just a parking state. It's okay to rely on the "refcount == 0" for state transition as far as I see. I will work towards this. Best regards, baolu