sid2groups keeps track of which stream id combinations belong to a
iommu_group to assign those correctly to devices.
When a iommu_group is freed a stale pointer will however remain in
sid2groups. This prevents devices with the same stream id combination
to ever be attached again (see below).
Fix that by creating a shadow copy of the stream id configuration
when a group is allocated for the first time and clear the sid2group
entry when that group is freed.

  # echo 1 >/sys/bus/pci/devices/0000\:03\:00.0/remove
  pci 0000:03:00.0: Removing from iommu group 1
  # echo 1 >/sys/bus/pci/rescan
  [...]
  pci 0000:03:00.0: BAR 0: assigned [mem 0x6a0000000-0x6a000ffff 64bit pref]
  pci 0000:03:00.0: BAR 2: assigned [mem 0x6a0010000-0x6a001ffff 64bit pref]
  pci 0000:03:00.0: BAR 6: assigned [mem 0x6c0100000-0x6c01007ff pref]
  tg3 0000:03:00.0: Failed to add to iommu group 1: -2
  [...]

Fixes: 46d1fb07 ("iommu/dart: Add DART iommu driver")
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Sven Peter <sven@svenpeter.dev>
Tested-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210924134502.15589-1-sven@svenpeter.devSigned-off-by: Joerg Roedel <jroedel@suse.de>