iommu/vt-d: Support asynchronous IOMMU nested capabilities

Current VT-d implementation supports nested translation only if all
underlying IOMMUs support the nested capability. This is unnecessary
as the upper layer is allowed to create different containers and set
them with different type of iommu backend. The IOMMU driver needs to
guarantee that devices attached to a nested mode iommu_domain should
support nested capabilility.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210517065701.5078-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20210610020115.1637656-6-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel/iommu.c

@@ -4757,6 +4757,13 @@ static int prepare_domain_attach_device(struct iommu_domain *domain,
 	if (!iommu)
 		return -ENODEV;
 
+	if ((dmar_domain->flags & DOMAIN_FLAG_NESTING_MODE) &&
+	    !ecap_nest(iommu->ecap)) {
+		dev_err(dev, "%s: iommu not support nested translation\n",
+			iommu->name);
+		return -EINVAL;
+	}
+
 	/* check if this iommu agaw is sufficient for max mapped address */
 	addr_width = agaw_to_width(iommu->agaw);
 	if (addr_width > cap_mgaw(iommu->cap))
@@ -5457,7 +5464,7 @@ intel_iommu_enable_nesting(struct iommu_domain *domain)
 	int ret = -ENODEV;
 
 	spin_lock_irqsave(&device_domain_lock, flags);
-	if (nested_mode_support() && list_empty(&dmar_domain->devices)) {
+	if (list_empty(&dmar_domain->devices)) {
 		dmar_domain->flags |= DOMAIN_FLAG_NESTING_MODE;
 		dmar_domain->flags &= ~DOMAIN_FLAG_USE_FIRST_LEVEL;
 		ret = 0;