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

Dan Rosenberg
2011-05-24T23:34:59Z

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.

Thanks,
Dan