iommu/virtio: Support bypass domains

The VIRTIO_IOMMU_F_BYPASS_CONFIG feature adds a new flag to the ATTACH
request, that creates a bypass domain. Use it to enable identity
domains.

When VIRTIO_IOMMU_F_BYPASS_CONFIG is not supported by the device, we
currently fail attaching to an identity domain. Future patches will
instead create identity mappings in this case.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20211201173323.1045819-3-jean-philippe@linaro.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/virtio-iommu.c

@@ -71,6 +71,7 @@ struct viommu_domain {
 	struct rb_root_cached		mappings;
 
 	unsigned long			nr_endpoints;
+	bool				bypass;
 };
 
 struct viommu_endpoint {
@@ -587,7 +588,9 @@ static struct iommu_domain *viommu_domain_alloc(unsigned type)
 {
 	struct viommu_domain *vdomain;
 
-	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
+	if (type != IOMMU_DOMAIN_UNMANAGED &&
+	    type != IOMMU_DOMAIN_DMA &&
+	    type != IOMMU_DOMAIN_IDENTITY)
 		return NULL;
 
 	vdomain = kzalloc(sizeof(*vdomain), GFP_KERNEL);
@@ -630,6 +633,17 @@ static int viommu_domain_finalise(struct viommu_endpoint *vdev,
 	vdomain->map_flags	= viommu->map_flags;
 	vdomain->viommu		= viommu;
 
+	if (domain->type == IOMMU_DOMAIN_IDENTITY) {
+		if (!virtio_has_feature(viommu->vdev,
+					VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
+			ida_free(&viommu->domain_ids, vdomain->id);
+			vdomain->viommu = NULL;
+			return -EOPNOTSUPP;
+		}
+
+		vdomain->bypass = true;
+	}
+
 	return 0;
 }
 
@@ -691,6 +705,9 @@ static int viommu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		.domain		= cpu_to_le32(vdomain->id),
 	};
 
+	if (vdomain->bypass)
+		req.flags |= cpu_to_le32(VIRTIO_IOMMU_ATTACH_F_BYPASS);
+
 	for (i = 0; i < fwspec->num_ids; i++) {
 		req.endpoint = cpu_to_le32(fwspec->ids[i]);
 
@@ -1132,6 +1149,7 @@ static unsigned int features[] = {
 	VIRTIO_IOMMU_F_DOMAIN_RANGE,
 	VIRTIO_IOMMU_F_PROBE,
 	VIRTIO_IOMMU_F_MMIO,
+	VIRTIO_IOMMU_F_BYPASS_CONFIG,
 };
 
 static struct virtio_device_id id_table[] = {