[v6,9/9] vring: Use the DMA API on Xen

Commit Message

Andy Lutomirski Feb. 1, 2016, 6 p.m. UTC

Signed-off-by: Andy Lutomirski <[e-mail]>
---
 drivers/virtio/virtio_ring.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Comments

David Vrabel Feb. 1, 2016, 6:03 p.m. UTC | #1

On 01/02/16 18:00, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <[e-mail]>

Reviewed-by: David Vrabel <[e-mail]>

Thanks.

David

Wei Liu Feb. 1, 2016, 9:26 p.m. UTC | #2

On Mon, Feb 01, 2016 at 10:00:59AM -0800, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <[e-mail]>

Reviewed-by: Wei Liu <[e-mail]>

Patch

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cf2840c7e500..2a921e5b1809 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(const struct vring_virtqueue *vq)
 {
+	/*
+	 * 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;
 }