Re: [RFC][PATCH] Randomize kernel base address on boot

H. Peter Anvin
2011-05-24T23:37:13Z

On 05/24/2011 04:34 PM, Dan Rosenberg wrote:
> On Tue, 2011-05-24 at 16:07 -0700, H. Peter Anvin wrote:
>> On 05/24/2011 04:04 PM, Dan Rosenberg wrote:
>>>
>>>> 2. Not introduce a performance regression (we avoid locating in the
>>>> bottom 16 MiB for performance reasons, except on very small systems);
>>>
>>> I altered the boot code so that it uses CONFIG_PHYSICAL_START, which
>>> defaults to 16 MiB, as a lower bound on location. So nothing will ever
>>> get loaded below there, and I still can take advantage of higher
>>> alignment granularity. Are there other problems I'm not anticipating?
>>>
>>
>> Please look at the discussion as to what led us to do things this way.
>>
>
> Would you be able to point me to said discussion? The only thing I can
> find is this:
>
> http://marc.info/?l=linux-kernel&m=124173552516435&w=2
>
> This set PHYSICAL_START at 16 MB and alignment at 2/4 MB. Then, three
> days later, this was committed:
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=ceefccc93932b920a8ec6f35f596db05202a12fe
>
> This sets the alignment to 16 MB, with the only justification being that
> relocatable kernels also need to start above 16 MB.
>

I think those patches came after the discussion were already over. I'll
try to look for it.

-hpa