Re: CVS commit: src/sys/arch

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Thu, Aug 03, 2017 at 04:20:45PM +0200, Maxime Villard wrote:
> > I was more thinking in terms of a single page in kernel VA, not in user
> > VA. That would side step most of the issues with dynamic LDT or having
> > to patch up the default LDT on context switches. That said, the latter
> > wouldn't be that difficult either, given that we already do that for the
> > GDT.
> 
> Mmh, not sure what you mean. If you mean a page that is a kernel page (in the
> sense of not having PG_u), then it's a privileged call gate, and we're back
> on the first issue (being in kernel mode, with user segment registers, and
> interrupts enabled). If you mean a page this a userland page (with PG_u), but
> located in the kernel VA range, that's not a good idea: it all of a sudden
> makes the map less consistent, and it is more complicated since the upper
> levels of the page tree need to have PG_u too.

I was thinking of a page in the kernel VA range that is accessible for
userland. I thought we had some of those already for the comm page, but
I might be misremember. We can also put it at the top of the user VA
range of course, i.e. where the stack used to originate.

Joerg