[RFC PATCH] vfio/type1: Do not support IOMMUs that allow bypass

[Alex Williamson <alex.williamson@redhat.com>]

We can only provide isolation if DMA is forced through the IOMMU
aperture.  Don't allow type1 to be used if this is not the case.

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

Eric, I see a number of IOMMU drivers enable this, do the ones you
care about for ARM set geometry.force_aperture?  Thanks,

Alex

 drivers/vfio/vfio_iommu_type1.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 57d8c37..6afa9d4 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -728,6 +728,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 	struct vfio_group *group, *g;
 	struct vfio_domain *domain, *d;
 	struct bus_type *bus = NULL;
+	struct iommu_domain_geometry geometry;
 	int ret;
 
 	mutex_lock(&iommu->lock);
@@ -762,6 +763,17 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 		goto out_free;
 	}
 
+	/*
+	 * If a domain does not force DMA within the aperture, devices are not
+	 * isolated and type1 is not an appropriate IOMMU model.
+	 */
+	ret = iommu_domain_get_attr(domain->domain,
+				    DOMAIN_ATTR_GEOMETRY, &geometry);
+	if (ret || !geometry.force_aperture) {
+		ret = -EPERM;
+		goto out_domain;
+	}
+
 	if (iommu->nesting) {
 		int attr = 1;