vring: Use the DMA API on Xen
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index e46d081..5c802d4 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -25,6 +25,7 @@
#include <linux/hrtimer.h>
#include <linux/kmemleak.h>
#include <linux/dma-mapping.h>
+#include <xen/xen.h>
#ifdef DEBUG
/* For development, we want to crash whenever the ring is screwed. */
@@ -136,6 +137,17 @@
static bool vring_use_dma_api(struct virtio_device *vdev)
{
+ /*
+ * In theory, it's possible to have a buggy QEMU-supposed
+ * emulated Q35 IOMMU and Xen enabled at the same time. On
+ * such a configuration, virtio has never worked and will
+ * not work without an even larger kludge. Instead, enable
+ * the DMA API if we're a Xen guest, which at least allows
+ * all of the sensible Xen configurations to work correctly.
+ */
+ if (xen_domain())
+ return true;
+
return false;
}