From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: Re: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device hot re-plug Date: Thu, 29 Aug 2019 17:08:18 +0800 Message-ID: References: <20190822142922.31526-1-janusz.krzysztofik@linux.intel.com> <3275480.HMaYE7B3nd@jkrzyszt-desk.ger.corp.intel.com> <0cf4e930-1132-1e7f-815b-57a08a1fe5de@linux.intel.com> <3255251.C7nBVfOIaa@jkrzyszt-desk.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <3255251.C7nBVfOIaa@jkrzyszt-desk.ger.corp.intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Janusz Krzysztofik Cc: baolu.lu@linux.intel.com, David Woodhouse , Joerg Roedel , iommu@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, =?UTF-8?Q?Micha=c5=82_Wajdeczko?= List-Id: intel-gfx@lists.freedesktop.org Hi, On 8/29/19 3:58 PM, Janusz Krzysztofik wrote: > Hi Baolu, > > On Thursday, August 29, 2019 3:43:31 AM CEST Lu Baolu wrote: >> Hi Janusz, >> >> On 8/28/19 10:17 PM, Janusz Krzysztofik wrote: >>>> We should avoid kernel panic when a intel_unmap() is called against >>>> a non-existent domain. >>> Does that mean you suggest to replace >>> BUG_ON(!domain); >>> with something like >>> if (WARN_ON(!domain)) >>> return; >>> and to not care of orphaned mappings left allocated? Is there a way to > inform >>> users that their active DMA mappings are no longer valid and they > shouldn't >>> call dma_unmap_*()? >>> >>>> But we shouldn't expect the IOMMU driver not >>>> cleaning up the domain info when a device remove notification comes and >>>> wait until all file descriptors being closed, right? >>> Shouldn't then the IOMMU driver take care of cleaning up resources still >>> allocated on device remove before it invalidates and forgets their > pointers? >>> >> >> You are right. We need to wait until all allocated resources (iova and >> mappings) to be released. >> >> How about registering a callback for BUS_NOTIFY_UNBOUND_DRIVER, and >> removing the domain info when the driver detachment completes? > > Device core calls BUS_NOTIFY_UNBOUND_DRIVER on each driver unbind, regardless > of a device being removed or not. As long as the device is not unplugged and > the BUS_NOTIFY_REMOVED_DEVICE notification not generated, an unbound driver is > not a problem here. > Morever, BUS_NOTIFY_UNBOUND_DRIVER is called even before > BUS_NOTIFY_REMOVED_DEVICE so that wouldn't help anyway. > Last but not least, bus events are independent of the IOMMU driver use via > DMA-API it exposes. Fair enough. > > If keeping data for unplugged devices and reusing it on device re-plug is not > acceptable then maybe the IOMMU driver should perform reference counting of > its internal resources occupied by DMA-API users and perform cleanups on last > release? I am not saying that keeping data is not acceptable. I just want to check whether there are any other solutions. Best regards, Baolu