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SubjectRe: [CFT][PATCH] 2.6.4-rc1 remove x86 boot page tables
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hpa@zytor.com (H. Peter Anvin) writes:

> 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.

Hmm. I will look at that.

> Also, you probably need to check that you didn't break 4G/4G,
> especially on SMP.

The patch will need a few tweaks but it should be fairly straight forward.

> 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.

Ok I have not seen that one. In this case there was enough common
code that it seemed reasonable to reuse it. I managed to reduce
the code to two tests. With just a bit of care I suspect I could
remove the tests completely.

> 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 :)

I will try. So far except for early_printk I have not found anything.
And that was easy to fix.

> 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.

Sounds like a good idea.

Eric
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