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

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Message-ID: <68BD4291-A757-475D-A1AC-582EF4ADE197@nvidia.com>
Date: Thu, 2 Oct 2025 00:48:49 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>
CC: John Hubbard <jhubbard@...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 Oct 1, 2025, at 7:56 PM, Danilo Krummrich <dakr@...nel.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@...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.

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.