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

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Message-ID: <8bc75706c18c410f9564805c487907aba0aab627.camel@linux.intel.com>
Date: Sun, 18 Jan 2026 15:29:02 +0100
From: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
To: Leon Romanovsky <leon@...nel.org>, 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>
Cc: 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 v2 2/4] dma-buf: Document revoke semantics

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?

Or perhaps I missed a prereq patch?

Thanks,
Thomas