On Wed, May 06, 2026 at 04:55:27PM +0100, Matt Evans wrote: > Hi Leon, > > On 06/05/2026 16:29, Leon Romanovsky wrote: > > > > On Wed, May 06, 2026 at 02:53:31PM +0100, Matt Evans wrote: > > > Hi Alex, > > > > > > On 01/05/2026 20:12, Alex Williamson wrote: > > > > > > > > On Thu, 16 Apr 2026 06:17:44 -0700 > > > > Matt Evans <[email protected]> wrote: > > > > > > > > > vfio_pci_dma_buf_cleanup() assumed all VFIO device DMABUFs need to be > > > > > revoked. However, if vfio_pci_dma_buf_move() revokes DMABUFs before > > > > > the fd/device closes, then vfio_pci_dma_buf_cleanup() would do a > > > > > second/underflowing kref_put() then wait_for_completion() on a > > > > > completion that never fires. Fixed by predicating on revocation > > > > > status. > > > > > > > > > > This could happen if PCI_COMMAND_MEMORY is cleared before closing the > > > > > device fd (but the scenario is more likely to hit when future commits > > > > > add more methods to revoke DMABUFs). > > > > > > > > > > Fixes: 1a8a5227f2299 ("vfio: Wait for dma-buf invalidation to > > > > > complete") > > > > > Signed-off-by: Matt Evans <[email protected]> > > > > > --- > > > > > > > > > > (Just a fix, but later "vfio/pci: Convert BAR mmap() to use a DMABUF" > > > > > and "vfio/pci: Permanently revoke a DMABUF on request" depend on this > > > > > context, so including in this series.) > > > > > > > > We really need a fix for this split out from this series, It's already > > > > been shown[1] that this is trivially reachable. Carlos proposed[2] a > > > > similar solution to the one below. I was concurrently working on the > > > > issued and suggested an alternative[3]. Let's pick a solution for > > > > 7.1-rc. Thanks, > > > > > > It looks like [3] is progressing, so I'll drop this one when I can rebase > > > onto it. > > > > > > I noticed [3] removes the dma_resv_lock(priv->dmabuf->resv) around the > > > priv->vdev = NULL, and this series' vfio_pci_mmap_huge_fault() relies on > > > vdev only changing whilst resv is held to resolve a race between a fault > > > and > > > cleanup (see patch 7 of this series). The handler takes resv so that it > > > can > > > stably test vdev in order to take memory_lock. > > > > I think that you should rely on priv->revoked and not on priv->vdev. > > Needs both unfortunately, as the fault handler ultimately needs to take > vdev->memory_lock.
One can argue that if priv->revoked == True, all accesses to device should be denied and treated as priv->vdev == Null. Thanks
