linux-kernel - Re: [PATCH 0/8] iommu/vt-d: Fix crash dump failure caused by legacy DMA/IO

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Date:	Wed, 15 Oct 2014 16:10:02 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Joerg Roedel <joro@...tes.org>,
	David Woodhouse <dwmw2@...radead.org>
CC:	Jerry.Hoemann@...com, indou.takao@...fujitsu.com, bhe@...hat.com,
	linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com, zhenhua@...com
Subject: Re: [PATCH 0/8] iommu/vt-d: Fix crash dump failure caused by legacy
 DMA/IO

David, Joerg,
I plan to merge this patch set with 3.17 stable kernel, and split this 
patch set into two :
1. The core part, including the changed functions, like [Patch 4/8], 
[Patch 8/8].
2. For the formatting issues, like [Patch 1/8],[Patch 3/8],  including 
the changes for code formations, creation of new files 
intel-iommu-kdump.c, intel-iommu-private.h.

I believe this will make the patch set more clear to read and understand.

What are your suggestions?

Thanks
Zhenhua


On 07/12/2014 12:27 AM, Jerry Hoemann wrote:
> On Wed, Jul 02, 2014 at 03:32:59PM +0200, Joerg Roedel wrote:
>> Hi David,
>>
>> On Wed, Apr 30, 2014 at 11:49:33AM +0100, David Woodhouse wrote:
>>> There could be all kinds of existing mappings in the DMA page tables,
>>> and I'm not sure it's safe to preserve them. What prevents the crashdump
>>> kernel from trying to use any of the physical pages which are
>>> accessible, and which could thus be corrupted by stray DMA?
>>>
>>> In fact, the old kernel could even have set up 1:1 passthrough mappings
>>> for some devices, which would then be able to DMA *anywhere*. Surely we
>>> need to prevent that?
>>
>> Ideally we would prevent that, yes. But the problem is that a failed DMA
>> transaction might put the device into an unrecoverable state. Usually
>> any in-flight DMA transactions should only target buffers set up by the
>> previous kernel and not corrupt any data.
>>
>>> After the last round of this patchset, we discussed a potential
>>> improvement where you point every virtual bus address at the *same*
>>> physical scratch page.
>>
>> That is a solution to prevent the in-flight DMA failures. But what
>> happens when there is some in-flight DMA to a disk to write some inodes
>> or a new superblock. Then this scratch address-space may cause
>> filesystem corruption at worst.
>>
>> So with this in mind I would prefer initially taking over the
>> page-tables from the old kernel before the device drivers re-initialize
>> the devices.
>>
>>
>> 	Joerg
>
> David, Joerg,
>
> What do you think here?  Do you want me to update the patch set for 3.17?
>
> Jerry
>

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