linux-kernel - Re: [PATCH 09/11] PCI: add matching checks for driver

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Date:   Wed, 16 Jun 2021 20:33:17 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Max Gurtovoy <mgurtovoy@...dia.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>, cohuck@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        aviadye@...dia.com, oren@...dia.com, shahafs@...dia.com,
        parav@...dia.com, artemp@...dia.com, kwankhede@...dia.com,
        ACurrid@...dia.com, cjia@...dia.com, yishaih@...dia.com,
        kevin.tian@...el.com, hch@...radead.org, targupta@...dia.com,
        shameerali.kolothum.thodi@...wei.com, liulongfang@...wei.com,
        yan.y.zhao@...el.com
Subject: Re: [PATCH 09/11] PCI: add matching checks for driver_override
 binding

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@...dia.com> 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
 
> -       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?

Thanks,
Jason