Re: New pmap module for m68k

> On Nov 9, 2025, at 11:10=E2=80=AFPM, Romain Dolbeau =
<[email protected]> wrote:
>=20
> s it possible to have more than one 32-bits space in the qemu model?
> That would be a way to create something equivalent to a 34-bits area.
> I am wondering if it would be possible to have UPA[1:0] (stored in
> bits [9:8] of descriptors, and the treated same as address bits all
> the way to the pins) used to discriminate between 4 32-bits area, that
> would give the virtual model e.g. 4 GiB of I/O space and up to 12 GiB
> of memory. The process virtual space would still be limited to <4 GiB,
> but several of them could be resident simultaneously. Completely
> useless on a real '040 (too much data, not enough speed), but might be
> handy on a build host.

I keep forgetting about the UPA bits (partially because the Hibler pmap =
uses one of them as a software-defined bit, which we thankfully got away =
with for all these years).

Yes, it would be possible to do that with UPA, but it would need special =
support in the pmap module (and any other place that has reason to =
consult a PTE value).

That said=E2=80=A6 I tried booting Qemu with 3.5GB and it errored out=E2=80=
=A6 Qemu itself does impose a limit, just above 3GB.

-- thorpej