Nouveau - Oct 2025 - [PATCH v2 1/2] rust: pci: skip probing VFs if driver doesn't support VFs

On Thu, Oct 02, 2025 at 09:36:17PM +0200, Danilo Krummrich
wrote:
> If we want to obtain the driver's private data from a device outside
the scope
> of bus callbacks, we always need to ensure that the device is guaranteed to
be
> bound and we also need to prove the type of the private data, since a
device
> structure can't be generic over its bound driver.
pci_iov_get_pf_drvdata() does both of these things - this is what it
is for. Please don't open code it :(
> > Certain conditions may be workable, some drivers seem to have
> > preferences not to call disable, though I think that is wrong :\
> 
> I fully agree! I was told that this is because apparently some PF drivers
are
> only loaded to enable SR-IOV and then removed to shrink the potential
attack
> surface. Personally, I think that's slightly paranoid, if the driver
would not
> do anything else than enable / disable SR-IOV, but I think we can work
around
> this use-case if people really want it.
I've heard worse reasons than that. If that is the interest I'd
suggest they should just use VFIO and leave a userspace stub
process..

Jason

On 10/2/25 11:04 PM, Jason Gunthorpe wrote:
> On Thu, Oct 02, 2025 at 09:36:17PM +0200, Danilo Krummrich wrote:
>> If we want to obtain the driver's private data from a device
outside the scope
>> of bus callbacks, we always need to ensure that the device is
guaranteed to be
>> bound and we also need to prove the type of the private data, since a
device
>> structure can't be generic over its bound driver.
> 
> pci_iov_get_pf_drvdata() does both of these things - this is what it
> is for. Please don't open code it :(
It makes no sense to use it, both of those things will be ensured in a more
generic way in the base device implementation already (which is what I meant
with layering).

Both requirements are not specific to PCI, or the specific VF -> PF use-case.

In order to guarantee soundness both of those things have to be guaranteed for
any access to the driver's private data.

I will send some patches soon, I think this will make it obvious.
:)
>>> Certain conditions may be workable, some drivers seem to have
>>> preferences not to call disable, though I think that is wrong :\
>>
>> I fully agree! I was told that this is because apparently some PF
drivers are
>> only loaded to enable SR-IOV and then removed to shrink the potential
attack
>> surface. Personally, I think that's slightly paranoid, if the
driver would not
>> do anything else than enable / disable SR-IOV, but I think we can work
around
>> this use-case if people really want it.
> 
> I've heard worse reasons than that. If that is the interest I'd
> suggest they should just use VFIO and leave a userspace stub
> process..
I'm not sure I follow your proposal, can you elaborate?