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

On Wed Oct 1, 2025 at 7:07 AM JST, John Hubbard wrote:
> Post-Kangrejos, the approach for NovaCore + VFIO has changed a bit: the
> idea now is that VFIO drivers, for NVIDIA GPUs that are supported by
> NovaCore, should bind directly to the GPU's VFs. (An earlier idea was
to
> let NovaCore bind to the VFs, and then have NovaCore call into the upper
> (VFIO) module via Aux Bus, but this turns out to be awkward and is no
> longer in favor.) So, in order to support that:
>
> Nova-core must only bind to Physical Functions (PFs) and regular PCI
> devices, not to Virtual Functions (VFs) created through SR-IOV.
Naive question: will guests also see the passed-through VF as a VF? If
so, wouldn't this change also prevents guests from using Nova?

On 9/30/25 5:26 PM, Alexandre Courbot wrote:
> On Wed Oct 1, 2025 at 7:07 AM JST, John Hubbard wrote:
>> Post-Kangrejos, the approach for NovaCore + VFIO has changed a bit: the
>> idea now is that VFIO drivers, for NVIDIA GPUs that are supported by
>> NovaCore, should bind directly to the GPU's VFs. (An earlier idea
was to
>> let NovaCore bind to the VFs, and then have NovaCore call into the
upper
>> (VFIO) module via Aux Bus, but this turns out to be awkward and is no
>> longer in favor.) So, in order to support that:
>>
>> Nova-core must only bind to Physical Functions (PFs) and regular PCI
>> devices, not to Virtual Functions (VFs) created through SR-IOV.
> 
> Naive question: will guests also see the passed-through VF as a VF? If
> so, wouldn't this change also prevents guests from using Nova?
I'm also new to this area. I would expect that guests *must* see
these as PFs, otherwise...nothing makes any sense.

Maybe Alex Williamson or Jason Gunthorpe (+CC) can chime in.

thanks,
-- 
John Hubbard

On 1.10.2025 3.26, Alexandre Courbot wrote:
> On Wed Oct 1, 2025 at 7:07 AM JST, John Hubbard wrote:
>> Post-Kangrejos, the approach for NovaCore + VFIO has changed a bit: the
>> idea now is that VFIO drivers, for NVIDIA GPUs that are supported by
>> NovaCore, should bind directly to the GPU's VFs. (An earlier idea
was to
>> let NovaCore bind to the VFs, and then have NovaCore call into the
upper
>> (VFIO) module via Aux Bus, but this turns out to be awkward and is no
>> longer in favor.) So, in order to support that:
>>
>> Nova-core must only bind to Physical Functions (PFs) and regular PCI
>> devices, not to Virtual Functions (VFs) created through SR-IOV.
> 
> Naive question: will guests also see the passed-through VF as a VF? If
> so, wouldn't this change also prevents guests from using Nova?
In the entire software stack (firmware and interface, host/guest 
driver,and management stack), the entire design assumes that a VF is
tied to a VM.

NVIDIA GPU already provides good enough mechanisms to enforce
those between containers on PF. Moreover, VF on baremetal is not the
only way to support *container* environments. Surely, there are also
other approaches, for example, PF driver with DRM cgroup.

Like what I mentioned, it is really device/use-case specific. The device
vendor chooses the best approaches based on their device characteristic
and schedule/resource isolation capabilities for supporting containers
on bare metal.

Z.