virtio-iommu: Clear IOMMUDevice when VFIO device is unplugged

virtio-iommu: Clear IOMMUDevice when VFIO device is unplugged

When a VFIO device is hoplugged in a VM using virtio-iommu, IOMMUPciBus
and IOMMUDevice cache entries are created in the .get_address_space()
handler of the machine IOMMU device. However, these entries are never
destroyed, not even when the VFIO device is detached from the machine.
This can lead to an assert if the device is reattached again.

When reattached, the .get_address_space() handler reuses an
IOMMUDevice entry allocated when the VFIO device was first attached.
virtio_iommu_set_host_iova_ranges() is called later on from the
.set_iommu_device() handler an fails with an assert on 'probe_done'
because the device appears to have been already probed when this is
not the case.

The IOMMUDevice entry is allocated in pci_device_iommu_address_space()
called from under vfio_realize(), the VFIO PCI realize handler. Since
pci_device_unset_iommu_device() is called from vfio_exitfn(), a sub
function of the PCIDevice unrealize() handler, it seems that the
.unset_iommu_device() handler is the best place to release resources
allocated at realize time. Clear the IOMMUDevice cache entry there to
fix hotplug.

Fixes: 817ef10da23c ("virtio-iommu: Implement set|unset]_iommu_device() callbacks")
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Message-Id: <20240701101453.203985-1-clg@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>