linux-kernel - Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

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Date:	Fri, 3 Apr 2015 14:05:36 +0000
From:	"Li, Zhen-Hua" <zhen-hual@...com>
To:	Dave Young <dyoung@...hat.com>
CC:	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"indou.takao@...fujitsu.com" <indou.takao@...fujitsu.com>,
	"bhe@...hat.com" <bhe@...hat.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"ddutile@...hat.com" <ddutile@...hat.com>,
	"ishii.hironobu@...fujitsu.com" <ishii.hironobu@...fujitsu.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"Hatch, Douglas B (HPS Linux PM)" <doug.hatch@...com>,
	"Hoemann, Jerry" <jerry.hoemann@...com>,
	"Vaden, Tom (HP Server OS Architecture)" <tom.vaden@...com>,
	"Zhang, Li (Zoe@...ervers-Core-OE-PSC)" <li.zhang6@...com>,
	"Mitchell, Lisa (MCLinux in Fort Collins)" <lisa.mitchell@...com>,
	"billsumnerlinux@...il.com" <billsumnerlinux@...il.com>,
	"Wright, Randy (HP Servers Linux)" <rwright@...com>
Subject: Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump
 kernel

The hardware will do some verification, but not completely.  If people think the OS should also do this, then it should be another patchset, I think.

Thanks
Zhenhua 

> 在 2015年4月3日，17:21，Dave Young <dyoung@...hat.com> 写道：
> 
>> 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.
> 
>> 
>> 
>> Thanks
>> Zhenhua
>> 
>> On 04/03/2015 04:40 PM, Dave Young wrote:
>>>> To fix this problem, we modifies the behaviors of the intel vt-d in the
>>>> crashdump kernel:
>>>> 
>>>> For DMA Remapping:
>>>> 1. To accept the vt-d hardware in an active state,
>>>> 2. Do not disable and re-enable the translation, keep it enabled.
>>>> 3. Use the old root entry table, do not rewrite the RTA register.
>>>> 4. Malloc and use new context entry table, copy data from the old ones that
>>>>   used by the old kernel.
>>> 
>>> Have not read all the patches, but I have a question, not sure this has been
>>> answered before. Old memory is not reliable, what if the old memory get corrupted
>>> before panic? Is it safe to continue using it in 2nd kernel, I worry that it will
>>> cause problems.
>>> 
>>> Hope I'm wrong though.
>>> 
>>> Thanks
>>> Dave
>>