vfio/type1: Add extension to test DMA cache coherence of IOMMU

Now that the type1 IOMMU backend can support IOMMU_CACHE, we need to
be able to test whether coherency is currently enforced.  Add an
extension for this.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -867,6 +867,23 @@ static void vfio_iommu_type1_release(void *iommu_data)
 	kfree(iommu);
 }
 
+static int vfio_domains_have_iommu_cache(struct vfio_iommu *iommu)
+{
+	struct vfio_domain *domain;
+	int ret = 1;
+
+	mutex_lock(&iommu->lock);
+	list_for_each_entry(domain, &iommu->domain_list, next) {
+		if (!(domain->prot & IOMMU_CACHE)) {
+			ret = 0;
+			break;
+		}
+	}
+	mutex_unlock(&iommu->lock);
+
+	return ret;
+}
+
 static long vfio_iommu_type1_ioctl(void *iommu_data,
 				   unsigned int cmd, unsigned long arg)
 {
@@ -878,6 +895,10 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
 		case VFIO_TYPE1_IOMMU:
 		case VFIO_TYPE1v2_IOMMU:
 			return 1;
+		case VFIO_DMA_CC_IOMMU:
+			if (!iommu)
+				return 0;
+			return vfio_domains_have_iommu_cache(iommu);
 		default:
 			return 0;
 		}

include/uapi/linux/vfio.h

@@ -24,6 +24,11 @@
 #define VFIO_TYPE1_IOMMU		1
 #define VFIO_SPAPR_TCE_IOMMU		2
 #define VFIO_TYPE1v2_IOMMU		3
+/*
+ * IOMMU enforces DMA cache coherence (ex. PCIe NoSnoop stripping).  This
+ * capability is subject to change as groups are added or removed.
+ */
+#define VFIO_DMA_CC_IOMMU		4
 
 /*
  * The IOCTL interface is designed for extensibility by embedding the