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authorMichael S. Tsirkin <mst@redhat.com>2016-04-18 12:58:14 +0300
committerMichael S. Tsirkin <mst@redhat.com>2016-08-01 21:44:52 +0300
commit1a937693993ff10d7e80cca6ddd55f3000aa6376 (patch)
tree77df81f5acf23d1c21240a625b5a8066b350e27a /include/linux/virtio_config.h
parent37cf99e08c6fb4dcea0f9ad2b13b6daa8c76a711 (diff)
downloadlinux-1a937693993ff10d7e80cca6ddd55f3000aa6376.tar.xz
virtio: new feature to detect IOMMU device quirk
The interaction between virtio and IOMMUs is messy. On most systems with virtio, physical addresses match bus addresses, and it doesn't particularly matter which one we use to program the device. On some systems, including Xen and any system with a physical device that speaks virtio behind a physical IOMMU, we must program the IOMMU for virtio DMA to work at all. On other systems, including SPARC and PPC64, virtio-pci devices are enumerated as though they are behind an IOMMU, but the virtio host ignores the IOMMU, so we must either pretend that the IOMMU isn't there or somehow map everything as the identity. Add a feature bit to detect that quirk: VIRTIO_F_IOMMU_PLATFORM. Any device with this feature bit set to 0 needs a quirk and has to be passed physical addresses (as opposed to bus addresses) even though the device is behind an IOMMU. Note: it has to be a per-device quirk because for example, there could be a mix of passed-through and virtual virtio devices. As another example, some devices could be implemented by an out of process hypervisor backend (in case of qemu vhost, or vhost-user) and so support for an IOMMU needs to be coded up separately. It would be cleanest to handle this in IOMMU core code, but that needs per-device DMA ops. While we are waiting for that to be implemented, use a work-around in virtio core. Note: a "noiommu" feature is a quirk - add a wrapper to make that clear. Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'include/linux/virtio_config.h')
-rw-r--r--include/linux/virtio_config.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 6e6cb0c9d7cb..26c155bb639b 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -149,6 +149,19 @@ static inline bool virtio_has_feature(const struct virtio_device *vdev,
return __virtio_test_bit(vdev, fbit);
}
+/**
+ * virtio_has_iommu_quirk - determine whether this device has the iommu quirk
+ * @vdev: the device
+ */
+static inline bool virtio_has_iommu_quirk(const struct virtio_device *vdev)
+{
+ /*
+ * Note the reverse polarity of the quirk feature (compared to most
+ * other features), this is for compatibility with legacy systems.
+ */
+ return !virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
+}
+
static inline
struct virtqueue *virtio_find_single_vq(struct virtio_device *vdev,
vq_callback_t *c, const char *n)