The current VFIO implementation allows pci-stub driver to be bound to
a PCI device with other devices in the same IOMMU group being assigned
to userspace. The pci-stub driver has no dependencies on DMA or the
IOVA mapping of the device, but it does prevent the user from having
direct access to the device, which is useful in some circumstances.

The pci_dma_configure() marks the iommu_group as containing only devices
with kernel drivers that manage DMA. For compatibility with the VFIO
usage, avoid this default behavior for the pci_stub. This allows the
pci_stub still able to be used by the admin to block driver binding after
applying the DMA ownership to VFIO.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20220418005000.897664-6-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>