diff options
| author | Andy Lutomirski <luto@kernel.org> | 2016-02-02 21:46:35 -0800 |
|---|---|---|
| committer | Alistair Strachan <astrachan@google.com> | 2019-01-16 12:42:08 -0800 |
| commit | dbe5b486ca9a7f537c0dc5bfe9f875948b43e91b (patch) | |
| tree | cd5c608fed5d1238696bd7742700faa78e82a1db | |
| parent | 5ec66a6767366c06e6a0c3f093dcf1d4e5aaa471 (diff) | |
UPSTREAM: vring: Introduce vring_use_dma_api()
This is a kludge, but no one has come up with a a better idea yet.
We'll introduce DMA API support guarded by vring_use_dma_api().
Eventually we may be able to return true on more and more systems,
and hopefully we can get rid of vring_use_dma_api() entirely some
day.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit d26c96c8102549f91eb0bea6196d54711ab52176)
Bug: 121166534
Test: Ran cuttlefish with android-4.4 + VSOCKETS, VMWARE_VMCI_VSOCKETS
Signed-off-by: Alistair Strachan <astrachan@google.com>
Change-Id: Icfe1fdb85df794d0238fef53123cd10d99d10aa4
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index a01a41a41269..eba6deb94685 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -104,6 +104,30 @@ struct vring_virtqueue { #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq) +/* + * The interaction between virtio and a possible IOMMU is a mess. + * + * On most systems with virtio, physical addresses match bus addresses, + * and it doesn't particularly matter whether we use the DMA API. + * + * On some systems, including Xen and any system with a physical device + * that speaks virtio behind a physical IOMMU, we must use the DMA API + * 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. + * + * For the time being, we preserve historic behavior and bypass the DMA + * API. + */ + +static bool vring_use_dma_api(struct virtio_device *vdev) +{ + return false; +} + static struct vring_desc *alloc_indirect(struct virtqueue *_vq, unsigned int total_sg, gfp_t gfp) { |