iommu/vt-d: Avoid unnecessary cache flush in pasid entry teardown

When a present pasid entry is disassembled, all kinds of pasid related
caches need to be flushed. But when a pasid entry is not being used
(PRESENT bit not set), we don't need to do this. Check the PRESENT bit
in intel_pasid_tear_down_entry() and avoid flushing caches if it's not
set.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210320025415.641201-6-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/pasid.c

@@ -517,6 +517,9 @@ void intel_pasid_tear_down_entry(struct intel_iommu *iommu, struct device *dev,
 	if (WARN_ON(!pte))
 		return;
 
+	if (!(pte->val[0] & PASID_PTE_PRESENT))
+		return;
+
 	did = pasid_get_domain_id(pte);
 	intel_pasid_clear_entry(dev, pasid, fault_ignore);