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

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Message-ID: <20251002210433.GH3299207@nvidia.com>
Date: Thu, 2 Oct 2025 18:04:33 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>
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 02, 2025 at 09:36:17PM +0200, Danilo Krummrich wrote:
> If we want to obtain the driver's private data from a device outside the scope
> of bus callbacks, we always need to ensure that the device is guaranteed to be
> bound and we also need to prove the type of the private data, since a device
> structure can't be generic over its bound driver.

pci_iov_get_pf_drvdata() does both of these things - this is what it
is for. Please don't open code it :(

> > Certain conditions may be workable, some drivers seem to have
> > preferences not to call disable, though I think that is wrong :\
> 
> I fully agree! I was told that this is because apparently some PF drivers are
> only loaded to enable SR-IOV and then removed to shrink the potential attack
> surface. Personally, I think that's slightly paranoid, if the driver would not
> do anything else than enable / disable SR-IOV, but I think we can work around
> this use-case if people really want it.

I've heard worse reasons than that. If that is the interest I'd
suggest they should just use VFIO and leave a userspace stub
process..

Jason