Re: [PAE support] Types + cosmetic fixes

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Feb 23, 2010 at 04:57:55PM +0100, Jean-Yves Migeon wrote:
> > I would like to see paddr_t and related types always be 64-bit,
> regardless
> > of whether the kernel is PAE enabled.  If not we effectively create a new
> > platform.
> 
> Yep, i386-pae. IMHO, modules cannot be "safely" shared between PAE and
> non-PAE.

Yes. And I don't think making paddr_t 64bits unconditionally would
make them magically compatible for modules. There would be other issues.

> 
> >  Do you envision any compatibility problems with userspace
> > applications from this change?
> 
> Typical userspace applications, no. However, I suspect that programs like
> crash(8) or libkvm would be affected by such a change. As well as those
> reading stuff directly in kmem.

I don't think so. kmem grovellers care about virtual addresses,
not physical addresses. At last I've not noticed anything bad with
i386PAE Xen kernels.

> 
> There is much more work for in-kernel code though; for example, iterating
> through the PDs/PTs is not as easy as iterating in a paddr_t array
> (consider a 64-bits paddr_t with a non-PAE kernel). We would have to split
> pd_entry_t from paddr_t, which is currently not the case.

Sure, you can't change the hardware to make the formats the same :)
I don't know if anything outside kernel tries to read the PTE though.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--