iommu/virtio: Reject IOMMU page granule larger than PAGE_SIZE

We don't currently support IOMMUs with a page granule larger than the
system page size. The IOVA allocator has a BUG_ON() in this case, and
VFIO has a WARN_ON().

Removing these obstacles ranges doesn't seem possible without major
changes to the DMA API and VFIO. Some callers of iommu_map(), for
example, want to map multiple page-aligned regions adjacent to each
others for scatter-gather purposes. Even in simple DMA API uses, a call
to dma_map_page() would let the endpoint access neighbouring memory. And
VFIO users cannot ensure that their virtual address buffer is physically
contiguous at the IOMMU granule.

Rather than triggering the IOVA BUG_ON() on mismatched page sizes, abort
the vdomain finalise() with an error message. We could simply abort the
viommu probe(), but an upcoming extension to virtio-iommu will allow
setting different page masks for each endpoint.
Reported-by: Bharat Bhushan <bbhushan2@marvell.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Bharat Bhushan <bbhushan2@marvell.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20200326093558.2641019-4-jean-philippe@linaro.orgSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/virtio-iommu.c

@@ -607,12 +607,22 @@ static struct iommu_domain *viommu_domain_alloc(unsigned type)
 	return &vdomain->domain;
 }
 
-static int viommu_domain_finalise(struct viommu_dev *viommu,
+static int viommu_domain_finalise(struct viommu_endpoint *vdev,
 				  struct iommu_domain *domain)
 {
 	int ret;
+	unsigned long viommu_page_size;
+	struct viommu_dev *viommu = vdev->viommu;
 	struct viommu_domain *vdomain = to_viommu_domain(domain);
 
+	viommu_page_size = 1UL << __ffs(viommu->pgsize_bitmap);
+	if (viommu_page_size > PAGE_SIZE) {
+		dev_err(vdev->dev,
+			"granule 0x%lx larger than system page size 0x%lx\n",
+			viommu_page_size, PAGE_SIZE);
+		return -EINVAL;
+	}
+
 	ret = ida_alloc_range(&viommu->domain_ids, viommu->first_domain,
 			      viommu->last_domain, GFP_KERNEL);
 	if (ret < 0)
@@ -659,7 +669,7 @@ static int viommu_attach_dev(struct iommu_domain *domain, struct device *dev)
 		 * Properly initialize the domain now that we know which viommu
 		 * owns it.
 		 */
-		ret = viommu_domain_finalise(vdev->viommu, domain);
+		ret = viommu_domain_finalise(vdev, domain);
 	} else if (vdomain->viommu != vdev->viommu) {
 		dev_err(dev, "cannot attach to foreign vIOMMU\n");
 		ret = -EXDEV;