[Qemu-devel] [PATCH/RFC 2/6] vfio: Ignore real IOMMUs if CONFIG_VFIO_NOIOMMU=y

[Geert Uytterhoeven <geert+renesas@glider.be>]

Allow use of the No-IOMMU mode even if a real IOMMU is present.
This is useful in case the device is not part of an actual IOMMU group.

Not-Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Question:
  - Some devices (e.g. rcar-gpio) don't use DMA, so why do they need an
    IOMMU group?
  - Even devices using DMA may do so using a separate DMAC module,
    pointed to by "dmas" DT properties (e.g. sh-sci), hence they may be
    not part of an IOMMU group.
  - How to know which devices do DMA?
---
 drivers/vfio/vfio.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 2bc3705a99bd2f1a..7736c3fbe468a3da 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -129,9 +129,13 @@ struct iommu_group *vfio_iommu_group_get(struct device *dev)
 	 * bus.  We set iommudata simply to be able to identify these groups
 	 * as special use and for reclamation later.
 	 */
-	if (group || !noiommu || iommu_present(dev->bus))
+	if (group || !noiommu)
 		return group;
 
+	if (iommu_present(dev->bus))
+		dev_warn(dev, "iommu present (%ps), ignoring\n",
+			 dev->bus->iommu_ops);
+
 	group = iommu_group_alloc();
 	if (IS_ERR(group))
 		return NULL;
-- 
2.7.4