Question regardin intel64 arch and page table setup

Eric W. Biederman ebiederm at
Wed Aug 11 20:22:49 EDT 2010

"H. Peter Anvin" <hpa at> writes:

> On 08/11/2010 02:51 PM, Eric W. Biederman wrote:
>> 3) I would start just getting the normal kexec case to work.
>>    The 64bit kernel does support starting at the 64bit entry point,
>>    but I don't think it has been tested if loaded above 4G.
> I can guarantee that it hasn't; I looked at that code not all that long
> ago and it's shock-full of 32- and 39-bit assumptions.

Ugh.  I thought I had purged the 32bit assumptions. I guess it has been
a while.  39-bit assumptions are forgivable, the architecture didn't
support more than 40bit physical addresses when it was written.

I wonder if this is a problem for SGI.  I remember on the ia64 NUMA
machines only node 0 had memory below 4GiB and so if you booted without
node 0 you had no memory below 4GiB.  I wonder if this restriction has
carried over to the x86_64 descendants of the Altix.

What is definitely true (unless someone has added an extension since last
I looked ) is that on a normal x86 smp architecture you can't start
additional processors without memory in the low 1MiB because that is all
you can specify in the startup ipi.


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