Re: [PATCH 09/11] PCI: add matching checks for driver_override binding

[Max Gurtovoy]

On 6/14/2021 9:42 PM, Alex Williamson wrote:
> On Sun, 13 Jun 2021 11:19:46 +0300
> Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote:
>
> > On 6/9/2021 4:27 AM, Alex Williamson wrote:
> > > On Tue, 8 Jun 2021 19:45:17 -0300
> > > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
> > >   
> > > > On Tue, Jun 08, 2021 at 03:26:43PM -0600, Alex Williamson wrote:
> > > > > > drivers that specifically opt into this feature and the driver now has
> > > > > > the opportunity to provide a proper match table that indicates what HW
> > > > > > it can properly support. vfio-pci continues to support everything.
> > > > > In doing so, this also breaks the new_id method for vfio-pci.
> > > > Does it? How? The driver_override flag is per match entry not for the
> > > > entire device so new_id added things will work the same as before as
> > > > their new match entry's flags will be zero.
> > > Hmm, that might have been a testing issue; combining driverctl with
> > > manual new_id testing might have left a driver_override in place.
> > >      
> > > > > Sorry, with so many userspace regressions, crippling the
> > > > > driver_override interface with an assumption of such a narrow focus,
> > > > > creating a vfio specific match flag, I don't see where this can go.
> > > > > Thanks,
> > > > On the other hand it overcomes all the objections from the last go
> > > > round: how userspace figures out which driver to use with
> > > > driver_override and integrating the universal driver into the scheme.
> > > >
> > > > pci_stub could be delt with by marking it for driver_override like
> > > > vfio_pci.
> > > By marking it a "vfio driver override"? :-\
> > >   
> > > > But driverctl as a general tool working with any module is not really
> > > > addressable.
> > > >
> > > > Is the only issue the blocking of the arbitary binding? That is not a
> > > > critical peice of this, IIRC
> > > We can't break userspace, which means new_id and driver_override need
> > > to work as they do now.  There are scads of driver binding scripts in
> > > the wild, for vfio-pci and other drivers.  We can't assume such a
> > > narrow scope.  Thanks,
> > what about the following code ?
> >
> > @@ -152,12 +152,28 @@ static const struct pci_device_id
> > *pci_match_device(struct pci_driver *drv,
> >           }
> >           spin_unlock(&drv->dynids.lock);
> >
> > -       if (!found_id)
> > -               found_id = pci_match_id(drv->id_table, dev);
> > +       if (found_id)
> > +               return found_id;
> a) A dynamic ID match always works regardless of driver override...
>
> > -       /* driver_override will always match, send a dummy id */
> > -       if (!found_id && dev->driver_override)
> > +       found_id = pci_match_id(drv->id_table, dev);
> > +       if (found_id) {
> > +               /*
> > +                * if we found id in the static table, we must fulfill the
> > +                * matching flags (i.e. if PCI_ID_F_DRIVER_OVERRIDE flag is
> > +                * set, driver_override should be provided).
> > +                */
> > +               bool is_driver_override =
> > +                       (found_id->flags & PCI_ID_F_DRIVER_OVERRIDE) != 0;
> > +               if ((is_driver_override && !dev->driver_override) ||
> b) A static ID match fails if the driver provides an override flag and
> the device does not have an override set, or...
>
> > +                   (dev->driver_override && !is_driver_override))
> c) The device has an override set and the driver does not support the
> override flag.
>
> > +                       return NULL;
> > +       } else if (dev->driver_override) {
> > +               /*
> > +                * if we didn't find suitable id in the static table,
> > +                * driver_override will still , send a dummy id
> > +                */
> >                   found_id = &pci_device_id_any;
> > +       }
> >
> >           return found_id;
> >    }
> >
> >
> > dynamic ids (new_id) works as before.
> >
> > Old driver_override works as before.
> This is deceptively complicated, but no, I don't believe it does.  By
> my understanding of c) an "old" driver can no longer use
> driver_override for binding a known device.  It seems that if we have a
> static ID match, then we cannot have a driver_override set for the
> device in such a case.  This is a userspace regression.

If I'll remove condition c) everyone will be happy ?

I really would like to end this ongoing discussion and finally have a 
clear idea of what we want.

By clear I mean C code.

If we'll continue raising ideas we'll never reach our goal. And my goal 
is the next merge window.

> > For "new" driver_override we must fulfill the new rules.
> For override'able drivers, the static table is almost useless other
> than using it for modules.alias support and potentially to provide
> driver_data.  As above, I find this all pretty confusing and I'd advise
> trying to write a concise set of rules outlining the behavior of
> driver_override vs dynamic IDs vs static IDs vs "override'able" driver
> flags.  I tried, I can't, it's convoluted and full of exceptions.
> Thanks,
>
> Alex