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

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Date:   Sun, 13 Jun 2021 11:19:46 +0300
From:   Max Gurtovoy <mgurtovoy@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     <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 6/9/2021 4:27 AM, Alex Williamson wrote:
> On Tue, 8 Jun 2021 19:45:17 -0300
> Jason Gunthorpe <jgg@...dia.com> 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;

-       /* 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) ||
+                   (dev->driver_override && !is_driver_override))
+                       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.

For "new" driver_override we must fulfill the new rules.

>
> Alex
>