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

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Message-ID: <20260119090440.GG13201@unreal>
Date: Mon, 19 Jan 2026 11:04:40 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
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>,
	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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	kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dma-buf: Document revoke semantics

On Sun, Jan 18, 2026 at 03:29:02PM +0100, Thomas Hellström wrote:
> On Sun, 2026-01-18 at 14:08 +0200, 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.
> 
> See previous comment WRT this.
> 
> > 
> > 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.
> 
> Why would the importer want to verify the exporter's support for
> revocation? If the exporter doesn't support it, the only consequence
> would be that invalidate_mappings() would never be called, and that
> dma_buf_pin() is a NOP. Besides, dma_buf_pin() would not return an
> error if the exporter doesn't implement the pin() callback?

The idea is that both should do revoke and there is a need to indicate
that this exporter has some expectations from the importers. One of them
is that invalidate_mappings exists.

Thanks

> 
> Or perhaps I missed a prereq patch?
> 
> Thanks,
> Thomas
> 
>