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

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Message-ID: <fb5c2be5-b104-4314-a1f5-728317d0ca53@nvidia.com>
Date: Tue, 30 Sep 2025 18:26:23 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>,
 Danilo Krummrich <dakr@...nel.org>
Cc: 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>, 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>,
 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 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