[coreboot] I've turned on paging as a test

Peter Stuge peter at stuge.se
Wed Mar 12 17:07:33 CET 2014

ron minnich wrote:
> > > I think the bigger question that we need to answer, now that we know
> > > it's doable, is whether we want paging or not. We may not.
> There's been confusion about terms such as paging and virtual memory
> in the past. So, to clear it up, 'paging' in this context means PGE
> is set in cr0

I do know what paging is. You and I even worked together on the GTT
page table at the Berlin meeting last year.

Maybe my point was too subtle. You have said many times in the past,
and I think it is a very good point, that we should be careful not to
turn coreboot into an operating system.

One might even dare say that this is a core value of the project.

> We have it today on ARM 32 and ARM V8.

Why is it helpful or neccessary there?

> We will have to have it on x86_64.

Why is it neccessary there?

> > > I was hoping it would give us a more convenient way to cover
> > > cache-disabled, write-back, and write-through ranges without
> > > all the fuss of MTRRs.
> >
> > I never like quick solutions because they're usually not good.
> I don't understand your comment.

I struggle when trying to explain it to Vladimir too. :\

> We first had platforms with paging 12 years ago. This is quick? :-)

When it was first used for matters less than how long it has been
considered for this particular use case. My concern is with the
following thought process:

- MTRRs sure make for a lot of fuss.
- I wish we could do something simpler.
- Let's turn on paging, that would be simpler!

I'm not saying that paging would not be simpler in some ways - I'm
saying that it seems like a big change, introducing codebase-wide
address indirection, for seemingly small gain of avoiding fuss with

Oh, and since we don't have a project-wide habit of distinguishing
between virtual and physical it seems that any use of paging
currently in coreboot can only be a big ugly hack. :\


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