On 1/21/26 10:36, Thomas Hellström wrote: > Hi, Christian, > > On Wed, 2026-01-21 at 10:20 +0100, Christian König wrote: >> On 1/20/26 15:07, Leon Romanovsky wrote: >>> From: Leon Romanovsky <[email protected]> >>> >>> 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 <[email protected]> >> >> Reviewed-by: Christian König <[email protected]> >> >> 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. > > I'm wondering shouldn't we require DMA_RESV_USAGE_BOOKKEEP here, as > *any* unsignaled fence could indicate access through the map?
Yes, exactly that. I totally missed this detail. Thanks a lot to Matthew and you to pointing this out. Regards, Christian. > > /Thomas > >> >> In other words you can only redirect the DMA-addresses previously >> given out into nirvana (or a dummy memory or similar), but you still >> need to avoid re-using them for something else. >> >> Regards, >> Christian. >> >>> --- >>> 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); >>> 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); >>>
