iommu/vt-d: Gracefully handle DMAR units with no supported address widths

Instead of bailing out completely, such a unit can still be used for
interrupt remapping.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/linux-iommu/549928db2de6532117f36c9c810373c14cf76f51.camel@infradead.org/Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/dmar.c

@@ -1024,8 +1024,8 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 {
 	struct intel_iommu *iommu;
 	u32 ver, sts;
-	int agaw = 0;
-	int msagaw = 0;
+	int agaw = -1;
+	int msagaw = -1;
 	int err;
 
 	if (!drhd->reg_base_addr) {
@@ -1050,17 +1050,28 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	}
 
 	err = -EINVAL;
+	if (cap_sagaw(iommu->cap) == 0) {
+		pr_info("%s: No supported address widths. Not attempting DMA translation.\n",
+			iommu->name);
+		drhd->ignored = 1;
+	}
+
+	if (!drhd->ignored) {
 		agaw = iommu_calculate_agaw(iommu);
 		if (agaw < 0) {
 			pr_err("Cannot get a valid agaw for iommu (seq_id = %d)\n",
 			       iommu->seq_id);
-		goto err_unmap;
+			drhd->ignored = 1;
+		}
 	}
+	if (!drhd->ignored) {
 		msagaw = iommu_calculate_max_sagaw(iommu);
 		if (msagaw < 0) {
 			pr_err("Cannot get a valid max agaw for iommu (seq_id = %d)\n",
 			       iommu->seq_id);
-		goto err_unmap;
+			drhd->ignored = 1;
+			agaw = -1;
+		}
 	}
 	iommu->agaw = agaw;
 	iommu->msagaw = msagaw;
@@ -1087,7 +1098,12 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 
 	raw_spin_lock_init(&iommu->register_lock);
 
-	if (intel_iommu_enabled) {
+	/*
+	 * This is only for hotplug; at boot time intel_iommu_enabled won't
+	 * be set yet. When intel_iommu_init() runs, it registers the units
+	 * present at boot time, then sets intel_iommu_enabled.
+	 */
+	if (intel_iommu_enabled && !drhd->ignored) {
 		err = iommu_device_sysfs_add(&iommu->iommu, NULL,
 					     intel_iommu_groups,
 					     "%s", iommu->name);
@@ -1117,7 +1133,7 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 
 static void free_iommu(struct intel_iommu *iommu)
 {
-	if (intel_iommu_enabled) {
+	if (intel_iommu_enabled && iommu->iommu.ops) {
 		iommu_device_unregister(&iommu->iommu);
 		iommu_device_sysfs_remove(&iommu->iommu);
 	}