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

[Max Gurtovoy]

On 6/17/2021 2:33 AM, Jason Gunthorpe wrote:
> On Thu, Jun 17, 2021 at 02:28:36AM +0300, Max Gurtovoy wrote:
> > On 6/16/2021 3:34 AM, Jason Gunthorpe wrote:
> > > On Tue, Jun 15, 2021 at 06:22:45PM -0600, Alex Williamson wrote:
> > > > On Tue, 15 Jun 2021 20:32:57 -0300
> > > > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
> > > >
> > > > > On Tue, Jun 15, 2021 at 05:22:42PM -0600, Alex Williamson wrote:
> > > > >
> > > > > > > > b) alone is a functional, runtime difference.
> > > > > > > I would state b) differently:
> > > > > > >
> > > > > > > b) Ignore the driver-override-only match entries in the ID table.
> > > > > > No, pci_match_device() returns NULL if a match is found that is marked
> > > > > > driver-override-only and a driver_override is not specified.  That's
> > > > > > the same as no match at all.  We don't then go on to search past that
> > > > > > match in the table, we fail to bind the driver.  That's effectively an
> > > > > > anti-match when there's no driver_override on the device.
> > > > > anti-match isn't the intention. The deployment will have match tables
> > > > > where all entires are either flags=0 or are driver-override-only.
> > > > I'd expect pci-pf-stub to have one of each, an any-id with
> > > > override-only flag and the one device ID currently in the table with
> > > > no flag.
> > > Oh Hum. Actually I think this shows the anti-match behavior is
> > > actually a bug.. :(
> > >
> > > For something like pci_pf_stub_whitelist, if we add a
> > > driver_override-only using the PCI any id then it effectively disables
> > > new_id completely because the match search will alway find the
> > > driver_override match first and stop searching. There is no chance to
> > > see things new_id adds.
> > Actually the dynamic table is the first table the driver search. So new_id
> > works exactly the same AFAIU.
> Oh, even better, so it isn't really an issue
>
> > But you're right for static mixed table (I assumed that this will never
> > happen I guess).
> Me too, we could organize the driver-overrides to be last

Yes we could, but in 2 years from now I'll forget this rule :)

And others may not be aware of it.

>   
> > -       found_id = pci_match_id(drv->id_table, dev);
> > -       if (found_id) {
> > +       ids = drv->id_table;
> > +       while ((found_id = pci_match_id(ids, dev))) {
> Yeah, keep searching makes logical sense to me
>
> > diff --git a/drivers/pci/pci-pf-stub.c b/drivers/pci/pci-pf-stub.c
> > index 45855a5e9fca..49544ba9a7af 100644
> > +++ b/drivers/pci/pci-pf-stub.c
> > @@ -19,6 +19,7 @@
> >    */
> >   static const struct pci_device_id pci_pf_stub_whitelist[] = {
> >          { PCI_VDEVICE(AMAZON, 0x0053) },
> > +       { PCI_DEVICE_FLAGS(PCI_ANY_ID, PCI_ANY_ID,
> > PCI_ID_F_STUB_DRIVER_OVERRIDE) }, /* match all by default (override) */
> >          /* required last entry */
> >          { 0 }
> And we don't really want this change any more right? No reason to put
> pci_stub in the module.alias file?

I actually did it in the patches I attached earlier.

It will look like:

stub_pci:v*d*sv*sd*bc*sc*i*

pci:v00001D0Fd00000053sv*sd*bc*sc*i*

I think it's good practice to avoid matching automatically and auto 
loading any_id_override and vfio_override drivers in general.

Do you see a reason not adding this alias for stub drivers but adding it 
to vfio_pci drivers ?

> Thanks,
> Jason