Nouveau - Oct 2025 - [PATCH 0/2] rust: pci: expose is_virtfn() and reject VFs in nova-core

On Thu Oct 2, 2025 at 1:51 AM CEST, John Hubbard wrote:
> On 10/1/25 4:47 PM, Joel Fernandes wrote:
>>> On Oct 1, 2025, at 7:00?PM, John Hubbard <jhubbard at
nvidia.com> wrote:
>>> ?On 10/1/25 3:52 PM, Danilo Krummrich wrote:
>>>>> On Thu Oct 2, 2025 at 12:38 AM CEST, John Hubbard wrote:
>>>>> On 10/1/25 6:52 AM, Zhi Wang wrote:
>>>>>> On 1.10.2025 13.32, Danilo Krummrich wrote:
>>>>>>> On Wed Oct 1, 2025 at 3:22 AM CEST, John Hubbard
wrote:
>>>>>>>> On 9/30/25 5:29 PM, Alistair Popple wrote:
>>>>>>>>> On 2025-10-01 at 08:07 +1000, John Hubbard
<jhubbard at nvidia.com> wrote...
>>>>> ...
>> Here is my opinion and correct me if I missed something:
>> 
>> It feels premature to remove the option of nova-core binding to a VF,
since other options to disable auto probing do exist as Jason pointed out.
>> 
>> Taking a parallel with VFIO pass through for instance, the user already
has to do some diligence like preventing drivers from binding and then making
vfio-pci bind to the device IDs. This case is similar though slightly different,
but VFIO setup requires some configuration anyway so will it really improve
anything?
>> 
>> I quietly suggest holding on till there is a real need or we are sure
nova cannot bind to, or operate on a VF. This
>
> I'm confident that nova-core cannot properly handle a VF with
*today's* code.
> There is no expectation at all for a VF to show up--yet.
>
> Which is why I think it's appropriate to skip it right now.
I agree with John.

If a driver does not support a certain device, it is not the user's
responsibility to prevent probing. Currently nova-core does not support VFs, so
it should never get probed for them in the first place.

> On Oct 1, 2025, at 7:56?PM, Danilo Krummrich <dakr at kernel.org>
wrote:
> 
> ?On Thu Oct 2, 2025 at 1:51 AM CEST, John Hubbard wrote:
>> On 10/1/25 4:47 PM, Joel Fernandes wrote:
>>>> On Oct 1, 2025, at 7:00?PM, John Hubbard <jhubbard at
nvidia.com> wrote:
>>>> ?On 10/1/25 3:52 PM, Danilo Krummrich wrote:
>>>>>> On Thu Oct 2, 2025 at 12:38 AM CEST, John Hubbard
wrote:
>>>>>> On 10/1/25 6:52 AM, Zhi Wang wrote:
>>>>>>> On 1.10.2025 13.32, Danilo Krummrich wrote:
>>>>>>>> On Wed Oct 1, 2025 at 3:22 AM CEST, John
Hubbard wrote:
>>>>>>>>> On 9/30/25 5:29 PM, Alistair Popple wrote:
>>>>>>>>>> On 2025-10-01 at 08:07 +1000, John
Hubbard <jhubbard at nvidia.com> wrote...
>>>>>> ...
>>> Here is my opinion and correct me if I missed something:
>>> 
>>> It feels premature to remove the option of nova-core binding to a
VF, since other options to disable auto probing do exist as Jason pointed out.
>>> 
>>> Taking a parallel with VFIO pass through for instance, the user
already has to do some diligence like preventing drivers from binding and then
making vfio-pci bind to the device IDs. This case is similar though slightly
different, but VFIO setup requires some configuration anyway so will it really
improve anything?
>>> 
>>> I quietly suggest holding on till there is a real need or we are
sure nova cannot bind to, or operate on a VF. This
>> 
>> I'm confident that nova-core cannot properly handle a VF with
*today's* code.
>> There is no expectation at all for a VF to show up--yet.
>> 
>> Which is why I think it's appropriate to skip it right now.
> 
> I agree with John.
> 
> If a driver does not support a certain device, it is not the user's
> responsibility to prevent probing. Currently nova-core does not support
VFs, so
> it should never get probed for them in the first place.
That works for me. If we are doing this, I would also suggest adding a detailed
comment preceding the if statement, saying the reason for this is because the
VFs share the same device IDs when in reality we have 2 different drivers that
handle the different functions.

Thanks.

On 10/1/25 5:48 PM, Joel Fernandes wrote:
>> On Oct 1, 2025, at 7:56?PM, Danilo Krummrich <dakr at kernel.org>
wrote:
>> ?On Thu Oct 2, 2025 at 1:51 AM CEST, John Hubbard wrote:
>>> On 10/1/25 4:47 PM, Joel Fernandes wrote:
>>>>> On Oct 1, 2025, at 7:00?PM, John Hubbard <jhubbard at
nvidia.com> wrote:
>>>>> ?On 10/1/25 3:52 PM, Danilo Krummrich wrote:
>>>>>>> On Thu Oct 2, 2025 at 12:38 AM CEST, John Hubbard
wrote:
>>>>>>> On 10/1/25 6:52 AM, Zhi Wang wrote:
>>>>>>>> On 1.10.2025 13.32, Danilo Krummrich wrote:
>>>>>>>>> On Wed Oct 1, 2025 at 3:22 AM CEST, John
Hubbard wrote:
>>>>>>>>>> On 9/30/25 5:29 PM, Alistair Popple
wrote:
>>>>>>>>>>> On 2025-10-01 at 08:07 +1000, John
Hubbard <jhubbard at nvidia.com> wrote...
>>>>>>> ...
>> If a driver does not support a certain device, it is not the user's
>> responsibility to prevent probing. Currently nova-core does not support
VFs, so
>> it should never get probed for them in the first place.
> 
> That works for me. If we are doing this, I would also suggest adding a
detailed comment preceding the if statement,
The nova-core piece that decides this is not an if statement. It's
a const. It really is cleaner. :)

 saying the reason for this is because the VFs share the same device IDs when in
reality we have 2 different drivers that handle the different
functions.
> 
I've got it passing tests already, I'll add appropriate comments and
post it
shortly, and let's see what you think.

thanks,
-- 
John Hubbard