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

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Message-ID: <cd95b92c-a23b-03a7-1dd3-9554b9d22955@nvidia.com>
Date:   Thu, 17 Jun 2021 02:28:36 +0300
From:   Max Gurtovoy <mgurtovoy@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Alex Williamson <alex.williamson@...hat.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 6/16/2021 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.

But you're right for static mixed table (I assumed that this will never 
happen I guess).

If we put the any_id_override id before the non_override AMAZON device 
entry in the pci-pf-stub we'll fail with the matching to the AMAZON device.

What about the bellow untested addition (also remove condition c):

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 296de7bc9dc9..2d46f6cd96f7 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -136,7 +136,7 @@ static const struct pci_device_id 
*pci_match_device(struct pci_driver *drv,
                                                     struct pci_dev *dev)
  {
         struct pci_dynid *dynid;
-       const struct pci_device_id *found_id = NULL;
+       const struct pci_device_id *found_id = NULL, *ids;

         /* When driver_override is set, only bind to the matching driver */
         if (dev->driver_override && strcmp(dev->driver_override, 
drv->name))
@@ -155,8 +155,8 @@ static const struct pci_device_id 
*pci_match_device(struct pci_driver *drv,
         if (found_id)
                 return found_id;

-       found_id = pci_match_id(drv->id_table, dev);
-       if (found_id) {
+       ids = drv->id_table;
+       while ((found_id = pci_match_id(ids, dev))) {
                 /*
                  * if we found id in the static table, we must fulfill the
                  * matching flags (i.e. if PCI_ID_F_DRIVER_OVERRIDE flag is
@@ -164,17 +164,19 @@ static const struct pci_device_id 
*pci_match_device(struct pci_driver *drv,
                  */
                 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;
+               if (is_driver_override && !dev->driver_override)
+                       ids = found_id++; /* continue searching */
+               else
+                       break;
         }

+       /*
+        * if no static match, driver_override will always match, send a 
dummy
+        * id.
+        */
+       if (!found_id && dev->driver_override)
+               found_id = &pci_device_id_any;
+
         return found_id;
  }

diff --git a/drivers/pci/pci-pf-stub.c b/drivers/pci/pci-pf-stub.c
index 45855a5e9fca..49544ba9a7af 100644
--- a/drivers/pci/pci-pf-stub.c
+++ 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 }
  };


>
> We have to fix this patch so flags isn't an anti-match to make it work
> without user regression.
>
> Jason