iommu/vt-d: Avoid freeing virtual machine domain in free_dmar_iommu()

Virtual machine domains are created by intel_iommu_domain_init() and
should be destroyed by intel_iommu_domain_destroy(). So avoid freeing
virtual machine domain data structure in free_dmar_iommu() when
doamin->iommu_count reaches zero, otherwise it may cause invalid
memory access because the IOMMU framework still holds references
to the domain structure.
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -1480,7 +1480,8 @@ static void free_dmar_iommu(struct intel_iommu *iommu)
 
 			domain = iommu->domains[i];
 			clear_bit(i, iommu->domain_ids);
-			if (domain_detach_iommu(domain, iommu) == 0)
+			if (domain_detach_iommu(domain, iommu) == 0 &&
+			    !domain_type_is_vm(domain))
 				domain_exit(domain);
 		}
 	}