From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18EE7C3A5A1 for ; Wed, 28 Aug 2019 14:18:21 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E91C122CED for ; Wed, 28 Aug 2019 14:18:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E91C122CED Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id C630830B6; Wed, 28 Aug 2019 14:18:20 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id E23E730B3 for ; Wed, 28 Aug 2019 14:18:03 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 442BC13A for ; Wed, 28 Aug 2019 14:18:03 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Aug 2019 07:18:02 -0700 X-IronPort-AV: E=Sophos;i="5.64,441,1559545200"; d="scan'208";a="174924210" Received: from jkrzyszt-desk.igk.intel.com (HELO jkrzyszt-desk.ger.corp.intel.com) ([172.22.244.17]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Aug 2019 07:18:00 -0700 From: Janusz Krzysztofik To: Lu Baolu Subject: Re: [RFC PATCH] iommu/vt-d: Fix IOMMU field not populated on device hot re-plug Date: Wed, 28 Aug 2019 16:17:53 +0200 Message-ID: <3275480.HMaYE7B3nd@jkrzyszt-desk.ger.corp.intel.com> Organization: Intel Technology Poland sp. z o.o. - ul. Slowackiego 173, 80-298 Gdansk - KRS 101882 - NIP 957-07-52-316 In-Reply-To: <8f505c10-6256-c561-1aea-b3817388c5b2@linux.intel.com> References: <20190822142922.31526-1-janusz.krzysztofik@linux.intel.com> <29020717.Hl6jQjRASr@jkrzyszt-desk.ger.corp.intel.com> <8f505c10-6256-c561-1aea-b3817388c5b2@linux.intel.com> MIME-Version: 1.0 Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, David Woodhouse , intel-gfx@lists.freedesktop.org, =?utf-8?B?TWljaGHFgg==?= Wajdeczko X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Wednesday, August 28, 2019 2:56:18 AM CEST Lu Baolu wrote: > Hi Janusz, > > On 8/27/19 5:35 PM, Janusz Krzysztofik wrote: > > Hi Lu, > > > > On Monday, August 26, 2019 10:29:12 AM CEST Lu Baolu wrote: > >> Hi Janusz, > >> > >> On 8/26/19 4:15 PM, Janusz Krzysztofik wrote: > >>> Hi Lu, > >>> > >>> On Friday, August 23, 2019 3:51:11 AM CEST Lu Baolu wrote: > >>>> Hi, > >>>> > >>>> On 8/22/19 10:29 PM, Janusz Krzysztofik wrote: > >>>>> When a perfectly working i915 device is hot unplugged (via sysfs) and > >>>>> hot re-plugged again, its dev->archdata.iommu field is not populated > >>>>> again with an IOMMU pointer. As a result, the device probe fails on > >>>>> DMA mapping error during scratch page setup. > >>>>> > >>>>> It looks like that happens because devices are not detached from their > >>>>> MMUIO bus before they are removed on device unplug. Then, when an > >>>>> already registered device/IOMMU association is identified by the > >>>>> reinstantiated device's bus and function IDs on IOMMU bus re-attach > >>>>> attempt, the device's archdata is not populated with IOMMU information > >>>>> and the bad happens. > >>>>> > >>>>> I'm not sure if this is a proper fix but it works for me so at least it > >>>>> confirms correctness of my analysis results, I believe. So far I > >>>>> haven't been able to identify a good place where the possibly missing > >>>>> IOMMU bus detach on device unplug operation could be added. > >>>> > >>>> Which kernel version are you testing with? Does it contain below commit? > >>>> > >>>> commit 458b7c8e0dde12d140e3472b80919cbb9ae793f4 > >>>> Author: Lu Baolu > >>>> Date: Thu Aug 1 11:14:58 2019 +0800 > >>> > >>> I was using an internal branch based on drm-tip which didn't contain this > >>> commit yet. Fortunately it has been already merged into drm-tip over last > >>> weekend and has effectively fixed the issue. > >> > >> Thanks for testing this. > > > > My testing appeared not sufficiently exhaustive. The fix indeed resolved my > > initially discovered issue of not being able to rebind the i915 driver to a > > re-plugged device, however it brought another, probably more serious problem > > to light. > > > > When an open i915 device is hot unplugged, IOMMU bus notifier now cleans up > > IOMMU info for the device on PCI device remove while the i915 driver is still > > not released, kept by open file descriptors. Then, on last device close, > > cleanup attempts lead to kernel panic raised from intel_unmap() on unresolved > > IOMMU domain. > > 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? Thanks, Janusz > Best regards, > Baolu > > > > > With commit 458b7c8e0dde reverted and my fix applied, both late device close > > and device re-plug work for me. However, I can realize that's probably still > > not a complete solution, possibly missing some protection against reuse of a > > removed device other than for cleanup. If you think that's the right way to > > go, I can work more on that. > > > > I've had a look at other drivers and found AMD is using somehow similar > > approach. On the other hand, looking at the IOMMU common code I couldn't > > identify any arrangement that would support deferred device cleanup. > > > > If that approach is not acceptable for Intel IOMMU, please suggest a way you'd > > like to have it resolved and I can try to implement it. > > > > Thanks, > > Janusz > > > >> Best regards, > >> Lu Baolu > >> > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu