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

Leon Romanovsky
2026-01-21T10:44:57Z

On Wed, Jan 21, 2026 at 11:41:48AM +0100, Christian König wrote:
> 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@nvidia.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@nvidia.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.

Will change.

>
> 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
> >>
>
>