Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S943253AbcJ1Cdt (ORCPT ); Thu, 27 Oct 2016 22:33:49 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:35983 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S943005AbcJ1Cdq (ORCPT ); Thu, 27 Oct 2016 22:33:46 -0400 Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices To: Kirti Wankhede , alex.williamson@redhat.com, pbonzini@redhat.com, kraxel@redhat.com, cjia@nvidia.com References: <1476739332-4911-1-git-send-email-kwankhede@nvidia.com> <1476739332-4911-5-git-send-email-kwankhede@nvidia.com> Cc: jike.song@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kevin.tian@intel.com, qemu-devel@nongnu.org, bjsdjshi@linux.vnet.ibm.com From: Alexey Kardashevskiy Message-ID: Date: Fri, 28 Oct 2016 13:18:53 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=koi8-r Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2958 Lines: 76 On 27/10/16 23:31, Kirti Wankhede wrote: > > > On 10/27/2016 12:50 PM, Alexey Kardashevskiy wrote: >> On 18/10/16 08:22, Kirti Wankhede wrote: >>> VFIO IOMMU drivers are designed for the devices which are IOMMU capable. >>> Mediated device only uses IOMMU APIs, the underlying hardware can be >>> managed by an IOMMU domain. >>> >>> Aim of this change is: >>> - To use most of the code of TYPE1 IOMMU driver for mediated devices >>> - To support direct assigned device and mediated device in single module >>> >>> Added two new callback functions to struct vfio_iommu_driver_ops. Backend >>> IOMMU module that supports pining and unpinning pages for mdev devices >>> should provide these functions. >>> Added APIs for pining and unpining pages to VFIO module. These calls back >>> into backend iommu module to actually pin and unpin pages. >>> >>> This change adds pin and unpin support for mediated device to TYPE1 IOMMU >>> backend module. More details: >>> - When iommu_group of mediated devices is attached, task structure is >>> cached which is used later to pin pages and page accounting. >> >> >> For SPAPR TCE IOMMU driver, I ended up caching mm_struct with >> atomic_inc(&container->mm->mm_count) (patches are on the way) instead of >> using @current or task as the process might be gone while VFIO container is >> still alive and @mm might be needed to do proper cleanup; this might not be >> an issue with this patchset now but still you seem to only use @mm from >> task_struct. >> > > Consider the example of QEMU process which creates VFIO container, QEMU > in its teardown path would release the container. How could container be > alive when process is gone? do_exit() in kernel/exit.c calls exit_mm() (which sets NULL to tsk->mm) first, and then releases open files by calling exit_files(). So container's release() does not have current->mm. > > Kirti > >> >> >>> - It keeps track of pinned pages for mediated domain. This data is used to >>> verify unpinning request and to unpin remaining pages while detaching, if >>> there are any. >>> - Used existing mechanism for page accounting. If iommu capable domain >>> exist in the container then all pages are already pinned and accounted. >>> Accouting for mdev device is only done if there is no iommu capable >>> domain in the container. >>> - Page accouting is updated on hot plug and unplug mdev device and pass >>> through device. >>> >>> Tested by assigning below combinations of devices to a single VM: >>> - GPU pass through only >>> - vGPU device only >>> - One GPU pass through and one vGPU device >>> - Linux VM hot plug and unplug vGPU device while GPU pass through device >>> exist >>> - Linux VM hot plug and unplug GPU pass through device while vGPU device >>> exist >>> >>> Signed-off-by: Kirti Wankhede >>> Signed-off-by: Neo Jia >>> Change-Id: I295d6f0f2e0579b8d9882bfd8fd5a4194b97bd9a >> >> -- Alexey