iommu/vt-d: Use a helper function to skip agaw for SL

An Intel iommu domain uses 5-level page table by default. If the iommu
that the domain tries to attach supports less page levels, the top level
page tables should be skipped. Add a helper to do this so that it could
be used in other places.
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20200516062101.29541-3-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-pasid.c

@@ -499,6 +499,25 @@ int intel_pasid_setup_first_level(struct intel_iommu *iommu,
 	return 0;
 }
 
+/*
+ * Skip top levels of page tables for iommu which has less agaw
+ * than default. Unnecessary for PT mode.
+ */
+static inline int iommu_skip_agaw(struct dmar_domain *domain,
+				  struct intel_iommu *iommu,
+				  struct dma_pte **pgd)
+{
+	int agaw;
+
+	for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) {
+		*pgd = phys_to_virt(dma_pte_addr(*pgd));
+		if (!dma_pte_present(*pgd))
+			return -EINVAL;
+	}
+
+	return agaw;
+}
+
 /*
  * Set up the scalable mode pasid entry for second only translation type.
  */
@@ -522,18 +541,12 @@ int intel_pasid_setup_second_level(struct intel_iommu *iommu,
 		return -EINVAL;
 	}
 
-	/*
-	 * Skip top levels of page tables for iommu which has less agaw
-	 * than default. Unnecessary for PT mode.
-	 */
 	pgd = domain->pgd;
-	for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) {
-		pgd = phys_to_virt(dma_pte_addr(pgd));
-		if (!dma_pte_present(pgd)) {
+	agaw = iommu_skip_agaw(domain, iommu, &pgd);
+	if (agaw < 0) {
 		dev_err(dev, "Invalid domain page table\n");
 		return -EINVAL;
 	}
-	}
 
 	pgd_val = virt_to_phys(pgd);
 	did = domain->iommu_did[iommu->seq_id];