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

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Message-ID: <20260121142528.GC13201@unreal>
Date: Wed, 21 Jan 2026 16:25:28 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Pranjal Shrivastava <praan@...gle.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, 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 02:22:31PM +0000, Pranjal Shrivastava wrote:
> On Wed, Jan 21, 2026 at 09:47:12AM -0400, Jason Gunthorpe wrote:
> > On Wed, Jan 21, 2026 at 02:59:16PM +0200, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@...dia.com>
> > > 
> > > Use the new dma_buf_attach_revocable() helper to restrict attachments to
> > > importers that support mapping invalidation.
> > > 
> > > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > > ---
> > >  drivers/vfio/pci/vfio_pci_dmabuf.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> > > index 5fceefc40e27..85056a5a3faf 100644
> > > --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> > > +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> > > @@ -31,6 +31,9 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
> > >  	if (priv->revoked)
> > >  		return -ENODEV;
> > >  
> > > +	if (!dma_buf_attach_revocable(attachment))
> > > +		return -EOPNOTSUPP;
> > > +
> > >  	return 0;
> > >  }
> > 
> > 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.
> > 
> > It's tricky that NULL pin ops means "I support pin" :|
> > 
> 
> I've been wondering about this for a while now, I've been sitting on the
> following:
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index a4d8f2ff94e4..962bce959366 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1133,6 +1133,8 @@ int dma_buf_pin(struct dma_buf_attachment *attach)
> 
>         if (dmabuf->ops->pin)
>                 ret = dmabuf->ops->pin(attach);
> +       else
> +               ret = -EOPNOTSUPP;
> 
>         return ret;
>  }
> 
> But didn't get a chance to dive in the history yet. I thought there's a
> good reason we didn't have it? Would it break exisitng dmabuf users?

Probably every importer which called to dma_buf_pin() while connecting
to existing exporters as many in tree implementation don't have ->pin()
implemented.

Thanks

> 
> Praan