On Wed, Jul 15, 2026 at 06:47:31PM +0100, Matt Evans wrote: > A VFIO DMABUF can export a subset of a BAR to userspace by fd; add > support for mmap() of this fd. This provides another route for a > process to map BARs, in which the process can only map a specific > subset of a BAR represented by the exported DMABUF. > > mmap() support enables userspace driver designs that safely delegate > access to BAR sub-ranges to other client processes by sharing a DMABUF > fd, without having to share the (omnipotent) VFIO device fd with them. > > Since the main VFIO BAR mmap() is now DMABUF-aware, the new mmap() reuses > the existing vm_ops. > > The lifecycle of an exported DMABUF remains decoupled from that of the > device fd it came from, i.e. the device fd could be closed with DMABUF > VMAs present, meaning a fault on a VMA could happen concurrently with > vfio_pci_dma_buf_cleanup(). > > To deal with this scenario, the fault handler now temporarily takes a > VFIO device registration to ensure the vdev remains valid, and then > vdev->memory_lock can be taken on it. > > Signed-off-by: Matt Evans <[email protected]>
Nice note on locking, enjoyed the lock dance! Reviewed-by: Pranjal Shrivastava <[email protected]> Thanks, Praan
