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

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Message-ID: <1FA2746D-6F73-4D5A-A0DC-803D0563A5D7@nvidia.com>
Date: Wed, 1 Oct 2025 23:47:36 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: John Hubbard <jhubbard@...dia.com>
CC: Danilo Krummrich <dakr@...nel.org>, 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 7:00 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...
>>> ...
>>> As I mentioned in the other fork of this thread, I do think this is
>>> a good start. So unless someone disagrees, I'd like to go with this
>>> series (perhaps with better wording in the commit messages, and maybe
>>> a better comment above the probe() failure return) for now.
>> 
>> Indicating whether the driver supports VFs through a boolean in struct
>> pci_driver is about the same effort (well, maybe slightly more), but solves the
>> problem in a cleaner way since it avoids probe() being called in the first
>> place. Other existing drivers benefit from that as well.
> 
> Yes, that is cleaner, and like you say, nearly as easy.
> 
>> 
>> Forget about the SR-IOV RFC I was talking about; I really just intended to offer
>> to take care of that. :)
> 
> I can send out a v2 with that "PCI driver bool: supports VFs" approach,
> glad to do that.

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 might also close the door to say any future testing we may do by binding to a VF for instance (yes we can delete a statement but..).

Just my suggestion, but I do not strongly oppose either.

thanks,

- Joel

> 
> 
> thanks,
> --
> John Hubbard
>