Re: [CFT][PATCH] 2.6.4-rc1 remove x86 boot page tables

[hpa@zytor.com (H. Peter Anvin)]

Followup to:  <m1vflp81kq.fsf@ebiederm.dsl.xmission.com>
By author:    ebiederm@xmission.com (Eric W. Biederman)
In newsgroup: linux.dev.kernel
> 
> I think I have accounted for the sub architectures but I don't have
> the hardware to test them.  For voyager and VISWS I actually changed
> some code so I would appreciate a confirmation I didn't break
> anything.  
> 

For VISWS I think you actually need to turn paging off explicitly.
Also, you probably need to check that you didn't break 4G/4G,
especially on SMP.

I would also like to remove the magic %bx, which I did in the version
of my patch sent to akpm and which is now in -mm (basically the SMP
trampoline jumps to a different entrypoint instead.)  In that patch,
%ebx is still used as a flag, but it's completely internal to head.S.

See ftp://ftp.kernel.org/pub/linux/kernel/people/hpa/earlymem-7.diff

> Thanks to HPA who got the ball started :)

:)

I definitely agree that simply using no paging until we have page
tables is by far the cleanest approach.  I felt that is was too high
risk for 2.6, basically because I'm a chicken, but more realistically
because I couldn't really see the effect on all subarchitectures, and
I didn't feel 100% confident that there wasn't anything that relied on
memory being dual mapped; however, I'm more than happy to be proven
wrong :)

Oh yes, with this change you should probably just move swapper_pg_dir
(and empty_zero_page?) into .bss like anything else that should be
zero after boot.

	-hpa