How does kdump deal with trampoline allocation?

H. Peter Anvin hpa at
Mon Dec 27 19:13:55 EST 2010

On 12/27/2010 04:06 PM, Vivek Goyal wrote:
> On Mon, Dec 27, 2010 at 12:31:20PM -0800, H. Peter Anvin wrote:
>> Hi guys,
>> I'm planning a major overhaul of the trampoline allocation in x86, and
>> I'm trying to understand how kdump deals with it.  The trampoline has to
>> be allocated in low memory (< 1 MiB) and obviously that doesn't include
>> the kdump area at all.
> Hi Peter,
> Kdump has the concept of backup area. We backup the contents of first
> 640KB of physical RAM in kdump reserved area and then allow kdump kernel
> to use first 640KB of memory. So any trampoline allocation can be done
> in low memory area without overwritting the contents of first kernel.

OK, that's straightforward.  That presumably means that the low 640K is
marked unused in the memory map that memblock sees during early startup.
 That fits very cleanly with the patches I'm doing.



H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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