linux-kernel - Re: [PATCH RESEND] intel/pinctrl: check capability offset is between MMIO region

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Date:   Wed, 24 Mar 2021 16:13:59 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
CC:     <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH RESEND] intel/pinctrl: check capability offset is between
 MMIO region

On Wed, Mar 24, 2021 at 04:22:44PM +0200, Andy Shevchenko wrote:
> On Wed, Mar 24, 2021 at 02:55:15PM +0100, Roger Pau Monné wrote:
> > On Wed, Mar 24, 2021 at 02:58:07PM +0200, Andy Shevchenko wrote:
> > > On Wed, Mar 24, 2021 at 01:31:18PM +0100, Roger Pau Monne wrote:
> > > Moreover, it seems you are bailing out and basically denying driver to load.
> > > This does look that capability is simply the first register that blows the setup.
> > > I think you have to fix something into Xen to avoid loading these drivers or
> > > check with something like pci_device_is_present() approach.
> > 
> > Is there a backing PCI device BAR for those MMIO regions that the
> > pinctrl driver is trying to access? AFAICT those regions are only
> > reported in the ACPI DSDT table on the _CRS method of the object (at
> > least on my system).
> 
> Unfortunately it does not expose PCI configuration space.

Are those regions supposed to be marked as reserved in the memory map,
or that's left to the discretion of the hardware vendor?

> > Doing something like pci_device_is_present would require a register
> > that we know will never return ~0 unless the device is not present. As
> > said above, maybe we could use REVID to that end?
> 
> Yes, that's good, see above.
> 
> WRT capabilities, if we crash we will see the report immediately on the
> hardware which has such an issue. (It's quite unlikely we will ever have one,
> that's why I consider it's not critical)

I would rather prefer to not crash, because I think the kernel should
only resort to crashing when there's no alternative, and here it's
perfectly fine to just print an error message and don't load the
driver. IMO I would rather boot without pinctrl than get a panic if
it turns out pinctrl capabilities list is somehow corrupted. It's a
long shot, but the check added in order to prevent this scenario is
minimal.

In any case I will send a new version with the REVID check and this
current patch.

Thanks, Roger.