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
