Linux-libre 4.8.2-gnupck-4.8.2-gnu

1 files changed, 16 insertions, 2 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 2ebf30e57..ed9c9eeed 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -117,7 +117,10 @@ struct vring_virtqueue {
 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 
 /*
- * The interaction between virtio and a possible IOMMU is a mess.
+ * Modern virtio devices have feature bits to specify whether they need a
+ * quirk and bypass the IOMMU. If not there, just use the DMA API.
+ *
+ * If there, the interaction between virtio and DMA API is messy.
  *
  * On most systems with virtio, physical addresses match bus addresses,
  * and it doesn't particularly matter whether we use the DMA API.
@@ -133,10 +136,18 @@ struct vring_virtqueue {
  *
  * For the time being, we preserve historic behavior and bypass the DMA
  * API.
+ *
+ * TODO: install a per-device DMA ops structure that does the right thing
+ * taking into account all the above quirks, and use the DMA API
+ * unconditionally on data path.
  */
 
 static bool vring_use_dma_api(struct virtio_device *vdev)
 {
+	if (!virtio_has_iommu_quirk(vdev))
+		return true;
+
+	/* Otherwise, we are left to guess. */
 	/*
 	 * In theory, it's possible to have a buggy QEMU-supposed
 	 * emulated Q35 IOMMU and Xen enabled at the same time.  On
@@ -156,7 +167,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
  * making all of the arch DMA ops work on the vring device itself
  * is a mess.  For now, we use the parent device for DMA ops.
  */
-struct device *vring_dma_dev(const struct vring_virtqueue *vq)
+static struct device *vring_dma_dev(const struct vring_virtqueue *vq)
 {
 	return vq->vq.vdev->dev.parent;
 }
@@ -417,6 +428,7 @@ unmap_release:
 	if (indirect)
 		kfree(desc);
 
+	END_USE(vq);
 	return -EIO;
 }
 
@@ -1101,6 +1113,8 @@ void vring_transport_features(struct virtio_device *vdev)
 			break;
 		case VIRTIO_F_VERSION_1:
 			break;
+		case VIRTIO_F_IOMMU_PLATFORM:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);