Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753620Ab3HVPlR (ORCPT ); Thu, 22 Aug 2013 11:41:17 -0400 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:57091 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752280Ab3HVPlQ (ORCPT ); Thu, 22 Aug 2013 11:41:16 -0400 Date: Thu, 22 Aug 2013 23:41:07 +0800 From: Wei Yang To: Alex Williamson Cc: Alexey Kardashevskiy , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, benh@au1.ibm.com, paulus@au1.ibm.com Subject: Re: [PATCH 2/2] powerpc/iommu: check dev->iommu_group before remove a device from iommu_group Message-ID: <20130822154107.GC7393@weiyang.vnet.ibm.com> Reply-To: Wei Yang References: <1376647687-20550-1-git-send-email-weiyang@linux.vnet.ibm.com> <1376647687-20550-3-git-send-email-weiyang@linux.vnet.ibm.com> <520DFBC8.4040509@ozlabs.ru> <20130819012945.GA8342@weiyang.vnet.ibm.com> <52117765.7010205@ozlabs.ru> <20130819015538.GB8342@weiyang.vnet.ibm.com> <5215BC76.10105@ozlabs.ru> <20130822075237.GA14479@weiyang.vnet.ibm.com> <1377185303.25163.13.camel@ul30vt.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377185303.25163.13.camel@ul30vt.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13082215-5490-0000-0000-00000406FD78 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4495 Lines: 114 On Thu, Aug 22, 2013 at 09:28:23AM -0600, Alex Williamson wrote: >On Thu, 2013-08-22 at 15:52 +0800, Wei Yang wrote: >> On Thu, Aug 22, 2013 at 05:23:34PM +1000, Alexey Kardashevskiy wrote: >> >On 08/19/2013 11:55 AM, Wei Yang wrote: >> >> On Mon, Aug 19, 2013 at 11:39:49AM +1000, Alexey Kardashevskiy wrote: >> >>> On 08/19/2013 11:29 AM, Wei Yang wrote: >> >>>> On Fri, Aug 16, 2013 at 08:15:36PM +1000, Alexey Kardashevskiy wrote: >> >>>>> On 08/16/2013 08:08 PM, Wei Yang wrote: >> >>>>>> --- >> >>>>>> arch/powerpc/kernel/iommu.c | 3 ++- >> >>>>>> 1 files changed, 2 insertions(+), 1 deletions(-) >> >>>>>> >> >>>>>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c >> >>>>>> index b20ff17..5abf7c3 100644 >> >>>>>> --- a/arch/powerpc/kernel/iommu.c >> >>>>>> +++ b/arch/powerpc/kernel/iommu.c >> >>>>>> @@ -1149,7 +1149,8 @@ static int iommu_bus_notifier(struct notifier_block *nb, >> >>>>>> case BUS_NOTIFY_ADD_DEVICE: >> >>>>>> return iommu_add_device(dev); >> >>>>>> case BUS_NOTIFY_DEL_DEVICE: >> >>>>>> - iommu_del_device(dev); >> >>>>>> + if (dev->iommu_group) >> >>>>>> + iommu_del_device(dev); >> >>>>>> return 0; >> >>>>>> default: >> >>>>>> return 0; >> >>>>>> >> >>>>> >> >>>>> This one seems redundant, no? >> >>>> >> >>>> Sorry for the late. >> >>>> >> >>>> Yes, these two patches have the same purpose to guard the system, while in two >> >>>> different places. One is in powernv platform, the other is in the generic iommu >> >>>> driver. >> >>>> >> >>>> The one in powernv platform is used to correct the original logic. >> >>>> >> >>>> The one in generic iommu driver is to keep system safe in case other platform to >> >>>> call iommu_group_remove_device() without the check. >> >>> >> >>> >> >>> But I am moving bus notifier to powernv code (posted a patch last week, >> >>> otherwise Freescale's IOMMU conflicted) so this won't be the case. >> >> >> >> Yes, I see the patch. >> >> >> >> This means other platforms, besides powernv, will check the dev->iommu_group >> >> before remove the device? This would be a convention? >> >> >> >> If this is the case, the second patch is enough. We don't need to check it in >> >> generic iommu driver. >> >> >> >> Since I am not very familiar with the code convention, I post these two >> >> patches together. This doesn't mean I need to push both of them. Your comments >> >> are welcome, lets me understand which one is more suitable in this case. >> > >> > >> >Ok. So. I included the check in the bus notifier which I moved to powernv >> >platform, I guess I'll repost the series soon. >> >> Thanks, this check will guard the powernv platform. >> >> > >> >Good luck with pushing the fix for drivers/iommu/iommu.c :) >> > >> >> Alex, >> >> Sorry for not including you in the very beginning, which may spend you more >> efforts to track previous mails in this thread. >> >> Do you think it is reasonable to check the dev->iommu_group in >> iommu_group_remove_device()? Or we can count on the bus notifier to check it? >> >> Welcome your suggestions~ > >I don't really see the point of patch 1/2. iommu_group_remove_device() >is specifically to remove a device from an iommu_group, so why would you >call it on a device that's not part of an iommu_group. If you want to >avoid testing dev->iommu_group, then implement the .remove_device >callback rather than using the notifier. Thanks, > You mean the .remove_device like intel_iommu_remove_device()? Hmm... this function didn't check the dev->iommu_group and just call iommu_group_remove_device(). I see this guard is put in iommu_bus_notifier(), which will check dev->iommu_group before invoke .remove_device. Let me explain the case to triger the problem a little. On some platform, like powernv, we implement another bus notifier when devices are added or removed in the system. Like Alexey mentioned, he missed the check for dev->iommu_group in the notifier before removing it from iommu_group. This trigger the crash. So do you think it is reasonable to guard the kernel in iommu_group_remove_device(), or we give the platform developers the responsibility to check the dev->iommu_group before calling it? Thanks~ >Alex -- Richard Yang Help you, Help me -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/