linux-kernel - Re: [PATCH v2 2/4] dma-buf: Document revoke semantics

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Message-ID: <20260119113938.GL13201@unreal>
Date: Mon, 19 Jan 2026 13:39:38 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Christian König <christian.koenig@....com>
Cc: Sumit Semwal <sumit.semwal@...aro.org>,
	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>,
	Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Alex Williamson <alex@...zbot.org>, 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,
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Subject: Re: [PATCH v2 2/4] dma-buf: Document revoke semantics

On Mon, Jan 19, 2026 at 11:56:16AM +0100, Christian König wrote:
> On 1/18/26 13:08, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> > 
> > Document a DMA-buf revoke mechanism that allows an exporter to explicitly
> > invalidate ("kill") a shared buffer after it has been handed out to
> > importers. Once revoked, all further CPU and device access is blocked, and
> > importers consistently observe failure.
> > 
> > This requires both importers and exporters to honor the revoke contract.
> > 
> > For importers, this means implementing .invalidate_mappings() and calling
> > dma_buf_pin() after the DMA‑buf is attached to verify the exporter’s support
> > for revocation.
> > 
> > For exporters, this means implementing the .pin() callback, which checks
> > the DMA‑buf attachment for a valid revoke implementation.
> > 
> > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > ---
> >  include/linux/dma-buf.h | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)

<...>

> > + * Returns true if DMA-buf importer honors revoke semantics, which is
> > + * negotiated with the exporter, by making sure that importer implements
> > + * .invalidate_mappings() callback and calls to dma_buf_pin() after
> > + * DMA-buf attach.
> 
> That wording is to unclear. Something like:
> 
> Returns true if the DMA-buf importer can handle invalidating it's mappings at any time, even after pinning a buffer.

<...>

> 
> That's clearly not a good name. But that is already discussed in another thread.

<...>

> Oh, we should have renamed that as well. Or maybe it is time to completely remove that config option.

<...>

> This is checking exporter and not importer capabilities, please drop.

<...>

> So when invalidate_mappings is implemented we need to be able to call it at any time. Yeah that sounds like a valid approach to me.
> 
> But we need to remove the RDNA callback with the warning then to properly signal that. And also please document that in the callback kerneldoc.

Will do, thanks

> 
> Regards,
> Christian.
> 
> > +}
> > +
> >  struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> >  					  struct device *dev);
> >  struct dma_buf_attachment *
> > 
>