From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752140AbbEKBb4 (ORCPT ); Sun, 10 May 2015 21:31:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42656 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751653AbbEKBby (ORCPT ); Sun, 10 May 2015 21:31:54 -0400 Message-ID: <554FCE21.7060208@redhat.com> Date: Sun, 10 May 2015 17:31:13 -0400 From: Don Dutile User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.8.0 MIME-Version: 1.0 To: Dave Young CC: Baoquan He , "Li, ZhenHua" , dwmw2@infradead.org, indou.takao@jp.fujitsu.com, joro@8bytes.org, vgoyal@redhat.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, kexec@lists.infradead.org, alex.williamson@redhat.com, ishii.hironobu@jp.fujitsu.com, bhelgaas@google.com, doug.hatch@hp.com, jerry.hoemann@hp.com, tom.vaden@hp.com, li.zhang6@hp.com, lisa.mitchell@hp.com, billsumnerlinux@gmail.com, rwright@hp.com Subject: Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel References: <1426743388-26908-1-git-send-email-zhen-hual@hp.com> <20150403084031.GF22579@dhcp-128-53.nay.redhat.com> <551E56F6.60503@hp.com> <20150403092111.GG22579@dhcp-128-53.nay.redhat.com> <20150405015453.GB1562@dhcp-17-102.nay.redhat.com> <20150407034622.GB7213@localhost.localdomain> <5523E5DB.2090001@redhat.com> <20150507140029.GC4559@localhost.localdomain> In-Reply-To: <20150507140029.GC4559@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/07/2015 10:00 AM, Dave Young wrote: > On 04/07/15 at 10:12am, Don Dutile wrote: >> On 04/06/2015 11:46 PM, Dave Young wrote: >>> On 04/05/15 at 09:54am, Baoquan He wrote: >>>> On 04/03/15 at 05:21pm, Dave Young wrote: >>>>> On 04/03/15 at 05:01pm, Li, ZhenHua wrote: >>>>>> Hi Dave, >>>>>> >>>>>> There may be some possibilities that the old iommu data is corrupted by >>>>>> some other modules. Currently we do not have a better solution for the >>>>>> dmar faults. >>>>>> >>>>>> But I think when this happens, we need to fix the module that corrupted >>>>>> the old iommu data. I once met a similar problem in normal kernel, the >>>>>> queue used by the qi_* functions was written again by another module. >>>>>> The fix was in that module, not in iommu module. >>>>> >>>>> It is too late, there will be no chance to save vmcore then. >>>>> >>>>> Also if it is possible to continue corrupt other area of oldmem because >>>>> of using old iommu tables then it will cause more problems. >>>>> >>>>> So I think the tables at least need some verifycation before being used. >>>>> >>>> >>>> Yes, it's a good thinking anout this and verification is also an >>>> interesting idea. kexec/kdump do a sha256 calculation on loaded kernel >>>> and then verify this again when panic happens in purgatory. This checks >>>> whether any code stomps into region reserved for kexec/kernel and corrupt >>>> the loaded kernel. >>>> >>>> If this is decided to do it should be an enhancement to current >>>> patchset but not a approach change. Since this patchset is going very >>>> close to point as maintainers expected maybe this can be merged firstly, >>>> then think about enhancement. After all without this patchset vt-d often >>>> raised error message, hung. >>> >>> It does not convince me, we should do it right at the beginning instead of >>> introduce something wrong. >>> >>> I wonder why the old dma can not be remap to a specific page in kdump kernel >>> so that it will not corrupt more memory. But I may missed something, I will >>> looking for old threads and catch up. >>> >>> Thanks >>> Dave >>> >> The (only) issue is not corruption, but once the iommu is re-configured, the old, >> not-stopped-yet, dma engines will use iova's that will generate dmar faults, which >> will be enabled when the iommu is re-configured (even to a single/simple paging scheme) >> in the kexec kernel. >> > > Don, so if iommu is not reconfigured then these faults will not happen? > > Baoquan and me has a confusion below today about iommu=off/intel_iommu=off: > > intel_iommu_init() > { > ... > > dmar_table_init(); > > disable active iommu translations; > > if (no_iommu || dmar_disabled) > goto out_free_dmar; > > ... > } > > Any reason not move no_iommu check to the begining of intel_iommu_init function? > > Thanks > Dave Looks like you could. > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >