linux-kernel - Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

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Message-ID: <20260121194506.GI13201@unreal>
Date: Wed, 21 Jan 2026 21:45:06 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Christian König <christian.koenig@....com>,
	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>,
	Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
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	Alex Williamson <alex@...zbot.org>,
	Ankit Agrawal <ankita@...dia.com>,
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Subject: Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

On Wed, Jan 21, 2026 at 12:01:40PM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 21, 2026 at 04:28:17PM +0100, Christian König wrote:
> > On 1/21/26 14:31, Jason Gunthorpe wrote:
> > > On Wed, Jan 21, 2026 at 10:20:51AM +0100, Christian König wrote:
> > >> On 1/20/26 15:07, Leon Romanovsky wrote:
> > >>> From: Leon Romanovsky <leonro@...dia.com>
> > >>>
> > >>> dma-buf invalidation is performed asynchronously by hardware, so VFIO must
> > >>> wait until all affected objects have been fully invalidated.
> > >>>
> > >>> Fixes: 5d74781ebc86 ("vfio/pci: Add dma-buf export support for MMIO regions")
> > >>> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > >>
> > >> Reviewed-by: Christian König <christian.koenig@....com>
> > >>
> > >> Please also keep in mind that the while this wait for all fences for
> > >> correctness you also need to keep the mapping valid until
> > >> dma_buf_unmap_attachment() was called.
> > > 
> > > Can you elaborate on this more?
> > > 
> > > I think what we want for dma_buf_attach_revocable() is the strong
> > > guarentee that the importer stops doing all access to the memory once
> > > this sequence is completed and the exporter can rely on it. I don't
> > > think this works any other way.
> > > 
> > > This is already true for dynamic move capable importers, right?
> > 
> > Not quite, no.
> 
> :(
> 
> It is kind of shocking to hear these APIs work like this with such a
> loose lifetime definition. Leon can you include some of these detail
> in the new comments?

If we can clarify what needs to be addressed for v5, I will proceed.  
At the moment, it's still unclear what is missing in v4.

Thanks