Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access

[John Garry]

On 19/12/2021 14:23, David Laight wrote:
> > > > > I have tested this on s390 with HAS_IOPORT=n and allyesconfig as well
> > > > > as running it with defconfig. I've also been using it on my Ryzen 3990X
> > > > > workstation with LEGACY_PCI=n for a few days. I do get about 60 MiB
> > > > > fewer modules compared with a similar config of v5.15.8. Hard to say
> > > > > which other systems might miss things of course.
> > > > >
> > > > > I have not yet worked on the discussed IOPORT_NATIVE flag. Mostly I'm
> > > > > wondering two things. For one it feels like that could be a separate
> > > > > change on top since HAS_IOPORT + LEGACY_PCI is already quite big.
> > > > > Secondly I'm wondering about good ways of identifying such drivers and
> > > > > how much this overlaps with the ISA config flag.
> > I was interesting in the IOPORT_NATIVE flag (or whatever we call it) as
> > it solves the problem of drivers which "unconditionally do inb()/outb()
> > without checking the validity of the address using firmware or other
> > methods first" being built for (and loaded on and crashing) unsuitable
> > systems. Such a problem is in [0]
> >
> > So if we want to support that later, then it seems that someone would
> > need to go back and re-edit many same driver Kconfigs – like hwmon, for
> > example. I think it's better to avoid that and do it now.
> Could you do something where valid arguments to inb() have to come
> from some kernel mapping/validation function and are never in the
> range [0x0, 0x10000).
> Then drivers that are cheating the system will fail.

That sounds like the solution which I had here:

https://lore.kernel.org/lkml/1610729929-188490-2-git-send-email-john.garry@xxxxxxxxxx/

It worked for the scenario I was interested in, but Arnd had some 
concerns, which you can check there.

> Or, maybe, only allow [0x0, 0x10000) on systems that have a suitable bus.
> With the mapping functions returning a different value (eg the KVA into
> the PCI master window) that can be separately verified.
> That would let drivers do (say) inb(0x120) on systems that have (something
> like) and ISA bus, but not on PCI-only systems which support PCI IO
> accesses through a physical address window.

I'm not sure how this would look in practice. What would the check for 
the suitable bus be?

Thanks,
John