linux-kernel - Re: [PATCH v2 1/2] rust: pci: skip probing VFs if driver doesn't support VFs

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Message-Id: <DD82CIS1RKUX.GRLSUUL05D8E@kernel.org>
Date: Thu, 02 Oct 2025 20:55:12 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Jason Gunthorpe" <jgg@...dia.com>
Cc: "John Hubbard" <jhubbard@...dia.com>, "Alexandre Courbot"
 <acourbot@...dia.com>, "Joel Fernandes" <joelagnelf@...dia.com>, "Timur
 Tabi" <ttabi@...dia.com>, "Alistair Popple" <apopple@...dia.com>, "Zhi
 Wang" <zhiw@...dia.com>, "Surath Mitra" <smitra@...dia.com>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Alex Williamson"
 <alex.williamson@...hat.com>, "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>, <linux-pci@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, "LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] rust: pci: skip probing VFs if driver doesn't
 support VFs

On Thu Oct 2, 2025 at 7:56 PM CEST, Jason Gunthorpe wrote:
> This is certainly one option, you can put #2 in an aux driver of the
> PF in a nova-sriov.ko module that is fully divorced from VFIO. It
> might go along with a nova-fwctl.ko module too.
>
> You could also just embed it in nova-core.ko and have it activate when
> the PF is booted in "vGPU" mode.
>
> Broadly I would suggest the latter. aux devices make most sense to
> cross subsystems. Micro splitting a single driver with aux devices
> will make more of a mess than required. Though a good motivating
> reason would be if nova-srvio.ko is large.

As mentioned in the other sub-thread, I'm fine with either approach, but I think
I'd also prefer folding it into nova-core.

> Then you have two more:
>
> 4) A PCI driver in a VM that creates a DRM subsystem device
>
> This is nova-core.ko + nova-drm.ko
>
> 5) A VF driver that creates a DRM subsystem device without a VM
>
> Zhi says the device can't do this, but lets assume it could, then I
> would expect this to be nova-core.ko + nova-drm.ko, same as #4.

Indeed, but there'd probably be an overlap between the logic in the VFIO driver
and the logic required in nova-core to make this use-case happen I suspect.