From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58566) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c1vCg-0000A8-4W for qemu-devel@nongnu.org; Wed, 02 Nov 2016 09:03:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c1vCc-0007ZX-3Z for qemu-devel@nongnu.org; Wed, 02 Nov 2016 09:03:42 -0400 Received: from mga11.intel.com ([192.55.52.93]:44531) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1c1vCb-0007Z1-Qe for qemu-devel@nongnu.org; Wed, 02 Nov 2016 09:03:38 -0400 Message-ID: <5819E358.4080706@intel.com> Date: Wed, 02 Nov 2016 21:00:08 +0800 From: Jike Song MIME-Version: 1.0 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> In-Reply-To: <64066f1a-3d25-fede-f383-078b5f8f0fa0@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kirti Wankhede Cc: Alexey Kardashevskiy , alex.williamson@redhat.com, pbonzini@redhat.com, kraxel@redhat.com, cjia@nvidia.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kevin.tian@intel.com, qemu-devel@nongnu.org, bjsdjshi@linux.vnet.ibm.com 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? -- Thanks, Jike