From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966114AbcKAOCU (ORCPT ); Tue, 1 Nov 2016 10:02:20 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:18867 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965998AbcKAOCQ (ORCPT ); Tue, 1 Nov 2016 10:02:16 -0400 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 01 Nov 2016 07:02:13 -0700 Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices To: Alexey Kardashevskiy , , , , References: <1476739332-4911-1-git-send-email-kwankhede@nvidia.com> <1476739332-4911-5-git-send-email-kwankhede@nvidia.com> CC: , , , , , X-Nvconfidentiality: public From: Kirti Wankhede Message-ID: <62ade373-6edc-c7f3-c205-200cf4fd211f@nvidia.com> Date: Tue, 1 Nov 2016 19:31:42 +0530 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.24.216.210] X-ClientProxiedBy: DRHKMAIL102.nvidia.com (10.25.59.16) To bgmail102.nvidia.com (10.25.59.11) 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 On 10/28/2016 7:48 AM, Alexey Kardashevskiy wrote: > 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. > Incrementing usage count (get_task_struct()) while saving task structure and decementing it (put_task_struct()) from release() should work here. Updating the patch. Thanks, Kirti