Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754013AbcKBNVZ (ORCPT ); Wed, 2 Nov 2016 09:21:25 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:17348 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753536AbcKBNVV (ORCPT ); Wed, 2 Nov 2016 09:21:21 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Tue, 01 Nov 2016 18:21:04 -0700 Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices To: Jike Song References: <1476739332-4911-1-git-send-email-kwankhede@nvidia.com> <1476739332-4911-5-git-send-email-kwankhede@nvidia.com> <62ade373-6edc-c7f3-c205-200cf4fd211f@nvidia.com> <45b517de-3766-e96b-fec0-2b77da4dcf8d@nvidia.com> <695ca09f-b332-d33a-22fb-073f03dfaebf@ozlabs.ru> <5819DA45.9000200@intel.com> <64066f1a-3d25-fede-f383-078b5f8f0fa0@nvidia.com> <5819E358.4080706@intel.com> CC: Alexey Kardashevskiy , , , , , , , , , X-Nvconfidentiality: public From: Kirti Wankhede Message-ID: <4918e17b-b586-1e6e-aa47-f3fcdd3c660d@nvidia.com> Date: Wed, 2 Nov 2016 18:48:20 +0530 MIME-Version: 1.0 In-Reply-To: <5819E358.4080706@intel.com> X-Originating-IP: [10.24.216.210] X-ClientProxiedBy: DRUKMAIL101.nvidia.com (10.25.59.19) To bgmail102.nvidia.com (10.25.59.11) Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1460 Lines: 40 On 11/2/2016 6:30 PM, Jike Song wrote: > On 11/02/2016 08:41 PM, Kirti Wankhede wrote: >> On 11/2/2016 5:51 PM, Jike Song wrote: >>> On 11/02/2016 12:09 PM, Alexey Kardashevskiy wrote: >>>> Or you could just reference and use @mm as KVM and others do. Or there is >>>> anything else you need from @current than just @mm? >>>> >>> >>> I agree. If @mm is the only thing needed, there is really no reason to >>> refer to the @task :-) >>> >> >> In vfio_lock_acct(), that is for page accounting, if mm->mmap_sem is >> already held then page accounting is deferred, where task structure is >> used to get mm and work is deferred only if mm exist: >> mm = get_task_mm(task); >> >> That is where this module need task structure. > > Kirti, > > By calling get_task_mm you hold a ref on @mm and save it in iommu, > whenever you want to do something like vfio_lock_acct(), use that mm > (as you said, if mmap_sem not accessible then defer it to a work, but > still @mm is the whole information), and put it after the usage. > > I still can't see any reason that the @task have to be saved. It's > always the @mm all the time. Did I miss anything? > If the process is terminated by SIGKILL, as Alexey mentioned in this mail thread earlier exit_mm() is called first and then all files are closed. From exit_mm(), task->mm is set to NULL. So from teardown path, we should call get_task_mm(task) to get current status intsead of using stale pointer. Thanks, Kirti.