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

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Date:   Thu, 17 Jun 2021 02:42:46 +0300
From:   Max Gurtovoy <mgurtovoy@...dia.com>
To:     Jason Gunthorpe <jgg@...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 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@...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

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