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

From: Li, ZhenHua
Date: Wed Oct 15 2014 - 04:10:31 EST

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?


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.


David, Joerg,

What do you think here? Do you want me to update the patch set for 3.17?


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