linux-kernel - Re: [PATCH 0/2] rust: pci: expose is_virtfn() and reject VFs in nova-core

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Message-Id: <DD7E4902SAFP.3JLTVDIKKCRWS@kernel.org>
Date: Thu, 02 Oct 2025 01:55:57 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "John Hubbard" <jhubbard@...dia.com>
Cc: "Joel Fernandes" <joelagnelf@...dia.com>, "Zhi Wang" <zhiw@...dia.com>,
 "Alistair Popple" <apopple@...dia.com>, "Alexandre Courbot"
 <acourbot@...dia.com>, "Timur Tabi" <ttabi@...dia.com>, "Surath Mitra"
 <smitra@...dia.com>, "David Airlie" <airlied@...il.com>, "Simona Vetter"
 <simona@...ll.ch>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>, "Miguel
 Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun
 Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
 "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
 "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>, "LKML"
 <linux-kernel@...r.kernel.org>, "Jason Gunthorpe" <jgg@...dia.com>, "Alex
 Williamson" <alex.williamson@...hat.com>
Subject: Re: [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@...dia.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@...dia.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.