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

[Li, ZhenHua]

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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