[Xen-devel] [PATCH v7 9/9] vring: Use the DMA API on Xen

[Andy Lutomirski <luto@xxxxxxxxxx>]

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index e46d08107a50..5c802d47892c 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 @@ struct vring_virtqueue {
 
 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;
 }
 
-- 
2.5.0


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