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

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Date:	Fri, 03 Apr 2015 17:01:42 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Dave Young <dyoung@...hat.com>
CC:	dwmw2@...radead.org, indou.takao@...fujitsu.com, bhe@...hat.com,
	joro@...tes.org, vgoyal@...hat.com,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
	alex.williamson@...hat.com, ddutile@...hat.com,
	ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com,
	doug.hatch@...com, jerry.hoemann@...com, tom.vaden@...com,
	li.zhang6@...com, lisa.mitchell@...com, billsumnerlinux@...il.com,
	rwright@...com, "Li, ZhenHua" <zhen-hual@...com>
Subject: Re: [PATCH v9 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

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.


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
>
>

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