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

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Message-ID: <015b25e6-cfe1-4110-963f-5f8dc4720d1b@amd.com>
Date: Wed, 21 Jan 2026 11:41:48 +0100
From: Christian König <christian.koenig@....com>
To: Matthew Brost <matthew.brost@...el.com>, Leon Romanovsky <leon@...nel.org>
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>,
 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,
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Subject: Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

On 1/20/26 21:44, Matthew Brost wrote:
> On Tue, Jan 20, 2026 at 04:07:06PM +0200, 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>
>> ---
>>  drivers/vfio/pci/vfio_pci_dmabuf.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
>> index d4d0f7d08c53..33bc6a1909dd 100644
>> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
>> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
>> @@ -321,6 +321,9 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
>>  			dma_resv_lock(priv->dmabuf->resv, NULL);
>>  			priv->revoked = revoked;
>>  			dma_buf_move_notify(priv->dmabuf);
>> +			dma_resv_wait_timeout(priv->dmabuf->resv,
>> +					      DMA_RESV_USAGE_KERNEL, false,
>> +					      MAX_SCHEDULE_TIMEOUT);
> 
> Should we explicitly call out in the dma_buf_move_notify() /
> invalidate_mappings kernel-doc that KERNEL slots are the mechanism
> for communicating asynchronous dma_buf_move_notify /
> invalidate_mappings events via fences?

Oh, I missed that! And no that is not correct.

This should be DMA_RESV_USAGE_BOOKKEEP so that we wait for everything.

Regards,
Christian.

> 
> Yes, this is probably implied, but it wouldn’t hurt to state this
> explicitly as part of the cross-driver contract.
> 
> Here is what we have now:
> 
>  	 * - Dynamic importers should set fences for any access that they can't
> 	 *   disable immediately from their &dma_buf_attach_ops.invalidate_mappings
>  	 *   callback.
> 
> Matt
> 
>>  			dma_resv_unlock(priv->dmabuf->resv);
>>  		}
>>  		fput(priv->dmabuf->file);
>> @@ -342,6 +345,8 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
>>  		priv->vdev = NULL;
>>  		priv->revoked = true;
>>  		dma_buf_move_notify(priv->dmabuf);
>> +		dma_resv_wait_timeout(priv->dmabuf->resv, DMA_RESV_USAGE_KERNEL,
>> +				      false, MAX_SCHEDULE_TIMEOUT);
>>  		dma_resv_unlock(priv->dmabuf->resv);
>>  		vfio_device_put_registration(&vdev->vdev);
>>  		fput(priv->dmabuf->file);
>>
>> -- 
>> 2.52.0
>>