intel-iommu: Only unlink device domains from iommu

intel-iommu: Only unlink device domains from iommu

commit 9b4554b21ed07e8556405510638171f0c787742a upstream.

Commit a97590e5 added unlinking domains from iommus to reciprocate the
iommu from domains unlinking that was already done.  We actually want
to only do this for device domains and never for the static
identity map domain or VM domains.  The SI domain is special and
never freed, while VM domain->id lives in their own special address
space, separate from iommu->domain_ids.

In the current code, a VM can get domain->id zero, then mark that
domain unused when unbound from pci-stub.  This leads to DMAR
write faults when the device is re-bound to the host driver.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>