Mailing List Archive

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@huawei.com/

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

On 20/12/2021 09:27, Niklas Schnelle wrote:
>> > My feeling is that in this case we want some other dependency, e.g. a
>> > new CONFIG_LPC. It should actually be possible to use this driver on
>> > any machine with an LPC bus, which would by definition be the primary
>> > I/O space, so it should be possible to load it on Arm64.
>>
>> You did suggest HARDCODED_IOPORT earlier in this thread, and the
>> definition/premise there seemed sensible to me.
>>
>> Anyway it seems practical to make all these changes in a single series,
>> so need a way forward as Niklas has no such changes for this additional
>> kconfig option.
>>
>> As a start, may I suggest we at least have Niklas' patch committed to a
>> dev branch based on -next or latest mainline release for further analysis?
>>
>> Thanks,
>> John
>>
>>
> My plan would be to split the patch up into more manageable pieces as
> suggested by Arnd plus of course fixes like the missing ARM select. As
> Arnd suggested I'll split the HAS_IOPORT additions into the initial
> introduction plus arch selects and then the HAS_IOPORT dependencies per
> subsytem. I think these per subsystem dependency patches then would be
> a great place to find drivers which should have a different dependency
> be it on LPC or a newly introduced HARDCODED_IOPORT. The thing is we
> can find and check HAS_IOPORT dependencies easily but it's hard to find
> HARDCODED_IOPORT so I think the lattter should be a refinement of the
> former. It can of course still go in as a single series. I'll
> definitely make the next iteration available as a git branch.

I'll do an audit for what would require HARDCODED_IOPORT to understand
the scope while you can continue the work on your current path.

Thanks,
john

On Tue, 2021-12-21 at 16:48 +0000, John Garry wrote:
> On 20/12/2021 09:27, Niklas Schnelle wrote:
> > > > My feeling is that in this case we want some other dependency, e.g. a
> > > > new CONFIG_LPC. It should actually be possible to use this driver on
> > > > any machine with an LPC bus, which would by definition be the primary
> > > > I/O space, so it should be possible to load it on Arm64.
> > >
> > > You did suggest HARDCODED_IOPORT earlier in this thread, and the
> > > definition/premise there seemed sensible to me.
> > >
> > > Anyway it seems practical to make all these changes in a single series,
> > > so need a way forward as Niklas has no such changes for this additional
> > > kconfig option.
> > >
> > > As a start, may I suggest we at least have Niklas' patch committed to a
> > > dev branch based on -next or latest mainline release for further analysis?
> > >
> > > Thanks,
> > > John
> > >
> > >
> > My plan would be to split the patch up into more manageable pieces as
> > suggested by Arnd plus of course fixes like the missing ARM select. As
> > Arnd suggested I'll split the HAS_IOPORT additions into the initial
> > introduction plus arch selects and then the HAS_IOPORT dependencies per
> > subsytem. I think these per subsystem dependency patches then would be
> > a great place to find drivers which should have a different dependency
> > be it on LPC or a newly introduced HARDCODED_IOPORT. The thing is we
> > can find and check HAS_IOPORT dependencies easily but it's hard to find
> > HARDCODED_IOPORT so I think the lattter should be a refinement of the
> > former. It can of course still go in as a single series. I'll
> > definitely make the next iteration available as a git branch.
>
> I'll do an audit for what would require HARDCODED_IOPORT to understand
> the scope while you can continue the work on your current path.
>
> Thanks,
> john
>

Sounds good, I'm open to adding such a config option given a clear
enough picture of what drivers it would affect. Meanwhile I've made
some progress splitting things up. I still need to do a bit more
testing and refining of comments before sending an RFC but if you're
curious you can check out the 'has_ioport' branch on my GitHub here:

https://github.com/niklas88/linux.git (still figuring out if/how I can
get a proper git.kernel.org branch/repository).

Thanks,
Niklas