Re: [PATCH 3/8] add mem64_min/max control

H. Peter Anvin
2012-11-18T04:55:46Z

On 11/17/2012 08:47 PM, Eric W. Biederman wrote:
>>
>> I don't think that is feasible; we need access to this structure
>> extremely early. I think if you're using the 64-bit entry point it
>> has to be an entry condition that those structures are mapped. It
>> simply becomes a precondition for using the 64-bit entry point.
>
> 64bit purgatory coming from kexec should be running with a page table
> that identity maps everything loaded by kexec and in practice all of
> memory.
>
> We should still be using that page table when we enter the new kernel.
>
> However then the 64bit kernel switches to it's own page tables.
>
> So after that point we potentially need early_ioremap, because the
> kernel's page tables may not have covered the boot_params. Certainly we
> need to do something to ensure the kernels page table covers boot_params.
>

The easy way to fix that is to do what we do on 32 bits: we copy it into
the bss before we turn paging on (the 64-bit equivalent is before we
switch to the new page tables.) That way we know where it is, at least
for the bounded-size data items.

-hpa

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