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

From	Andy Lutomirski <luto@kernel.org>
Newsgroups	linux.kernel
Subject	[PATCH v7 9/9] vring: Use the DMA API on Xen
Date	2016-02-03 06:50 +0100
Message-ID	<qXYud-6cO-1@gated-at.bofh.it> (permalink)
References	<qXYud-6cO-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 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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[PATCH v7 9/9] vring: Use the DMA API on Xen Andy Lutomirski <luto@kernel.org> - 2016-02-03 06:50 +0100
  Re: [PATCH v7 9/9] vring: Use the DMA API on Xen David Vrabel <david.vrabel@citrix.com> - 2016-02-03 10:50 +0100
    Re: [PATCH v7 9/9] vring: Use the DMA API on Xen Andy Lutomirski <luto@amacapital.net> - 2016-02-04 18:50 +0100

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