linux-kernel - Re: [PATCH v4 8/8] vfio: Validate dma-buf revocation semantics

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Message-ID: <20260121154137.GD961572@ziepe.ca>
Date: Wed, 21 Jan 2026 11:41:37 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Leon Romanovsky <leon@...nel.org>
Cc: Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Alex Deucher <alexander.deucher@....com>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Dmitry Osipenko <dmitry.osipenko@...labora.com>,
	Gurchetan Singh <gurchetansingh@...omium.org>,
	Chia-I Wu <olvaffe@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Lucas De Marchi <lucas.demarchi@...el.com>,
	Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Felix Kuehling <Felix.Kuehling@....com>,
	Alex Williamson <alex@...zbot.org>,
	Ankit Agrawal <ankita@...dia.com>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
	amd-gfx@...ts.freedesktop.org, virtualization@...ts.linux.dev,
	intel-xe@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH v4 8/8] vfio: Validate dma-buf revocation semantics

On Wed, Jan 21, 2026 at 04:47:01PM +0200, Leon Romanovsky wrote:
> > We need to push an urgent -rc fix to implement a pin function here
> > that always fails. That was missed and it means things like rdma can
> > import vfio when the intention was to block that. It would be bad for
> > that uAPI mistake to reach a released kernel.
> 
> I don't see any urgency here. In the current kernel, the RDMA importer
> prints a warning to indicate it was attached to the wrong exporter.
> VFIO also invokes dma_buf_move_notify().

The design of vfio was always that it must not work with RDMA because
we cannot tolerate the errors that happen due to ignoring the
move_notify.

The entire purpose of this series could be stated as continuing to
block RDMA while opening up other pining users.

So it must be addressed urgently before someone builds an application
relying on this connection.

Jason