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

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Message-ID: <20251002120504.GD3195801@nvidia.com>
Date: Thu, 2 Oct 2025 09:05:04 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	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>,
	Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH 0/2] rust: pci: expose is_virtfn() and reject VFs in
 nova-core

On Wed, Oct 01, 2025 at 05:54:45PM -0700, John Hubbard wrote:

>  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.

That's the fundamental problem here. Presenting the same device ID
when the device actually has a very different programming model is
against how PCI is supposed to operate.

For examplem mlx5 devices give unique IDs to their VFs - though they
don't have different programming models.

If novacore doesn't work on VFs at all, even in VMs, then use the
register based detection that was said earlier.

Jason