Re: [Fastboot] [PATCH] Reserving backup region for kexec basedcrashdumps.

[Hirokazu Takahashi]

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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