iommu/vt-d: Prepare for set_dev_pasid callback

The domain_flush_pasid_iotlb() helper function is used to flush the IOTLB
entries for a given PASID. Previously, this function assumed that
RID2PASID was only used for the first-level DMA translation. However, with
the introduction of the set_dev_pasid callback, this assumption is no
longer valid.

Add a check before using the RID2PASID for PASID invalidation. This check
ensures that the domain has been attached to a physical device before
using RID2PASID.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20230802212427.1497170-7-jacob.jun.pan@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/iommu.c

@@ -1475,7 +1475,8 @@ static void domain_flush_pasid_iotlb(struct intel_iommu *iommu,
 	unsigned long flags;
 
 	spin_lock_irqsave(&domain->lock, flags);
-	qi_flush_piotlb(iommu, did, IOMMU_NO_PASID, addr, npages, ih);
+	if (!list_empty(&domain->devices))
+		qi_flush_piotlb(iommu, did, IOMMU_NO_PASID, addr, npages, ih);
 	spin_unlock_irqrestore(&domain->lock, flags);
 }