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SubjectRe: [Fastboot] [PATCH] Reserving backup region for kexec based crashdumps.
From
Hi Eric,

> > Hi Vivek and Eric,
> >
> > IMHO, why don't we swap not only the contents of the top 640K
> > but also kernel working memory for kdump kernel?
> >
> > I guess this approach has some good points.
> >
> > 1.Preallocating reserved area is not mandatory at boot time.
> > And the reserved area can be distributed in small pieces
> > like original kexec does.
> >
> > 2.Special linking is not required for kdump kernel.
> > Each kdump kernel can be linked in the same way,
> > where the original kernel exists.
> >
> > Am I missing something?
>
> Preallocating the reserved area is largely to keep it from
> being the target of DMA accesses. Since we are not able
> to shutdown any of the drivers in the primary kernel running
> in a normal swath of memory sounds like a good way to get
> yourself stomped at the worst possible time.

So what do you think my another idea?

I think we can always make a kdump kernel mapped to the same virtual
address. So we will be free from caring about the physical address
where the kdump kernel is loaded.

I believe the memsection functionality which LHMS project is working
on would help this.

+
|
|
(user space)
|
|
physical | virtual
memory | space
+ ------------ +
| |
| |
| |
+ ------------.+
original | . | map kdump kernel here
kernel | . |
| . |
| . .+
+ . . |
| . . |
+ . |
kdump | . |
kernel | . |
| . |
+ |
| |
| |
| |


Thanks,
Hirokazu Takahashi.
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