[RFC PATCH kernel] vfio: Skip checking for IOMMU_CAP_CACHE_COHERENCY on POWER and more

VFIO on POWER does not implement iommu_ops and therefore iommu_capable()
always returns false and __iommu_group_alloc_blocking_domain() always
fails.

iommu_group_claim_dma_owner() in setting container fails for the same
reason - it cannot allocate a domain.

This skips the check for platforms supporting VFIO without implementing
iommu_ops which to my best knowledge is POWER only.

This also allows setting container in absence of iommu_ops.

Fixes: 70693f470848 ("vfio: Set DMA ownership for VFIO devices")
Fixes: e8ae0e140c05 ("vfio: Require that devices support DMA cache coherence")
Signed-off-by: Alexey Kardashevskiy <[email protected]>
---

Not quite sure what the proper small fix is and implementing iommu_ops
on POWER is not going to happen any time soon or ever :-/

---
 drivers/vfio/vfio.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 61e71c1154be..71408ab26cd0 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -605,7 +605,8 @@ int vfio_register_group_dev(struct vfio_device *device)
 	 * VFIO always sets IOMMU_CACHE because we offer no way for userspace to
 	 * restore cache coherency.
 	 */
-	if (!iommu_capable(device->dev->bus, IOMMU_CAP_CACHE_COHERENCY))
+	if (device->dev->bus->iommu_ops &&
+	    !iommu_capable(device->dev->bus, IOMMU_CAP_CACHE_COHERENCY))
 		return -EINVAL;
 
 	return __vfio_register_dev(device,
@@ -934,7 +935,7 @@ static void __vfio_group_unset_container(struct vfio_group *group)
 		driver->ops->detach_group(container->iommu_data,
 					  group->iommu_group);
 
-	if (group->type = VFIO_IOMMU)
+	if (group->type = VFIO_IOMMU && iommu_group_dma_owner_claimed(group->iommu_group))
 		iommu_group_release_dma_owner(group->iommu_group);
 
 	group->container = NULL;
@@ -1010,9 +1011,8 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 	}
 
 	if (group->type = VFIO_IOMMU) {
-		ret = iommu_group_claim_dma_owner(group->iommu_group, f.file);
-		if (ret)
-			goto unlock_out;
+		if (iommu_group_claim_dma_owner(group->iommu_group, f.file))
+			pr_warn("Failed to claim DMA owner");
 	}
 
 	driver = container->iommu_driver;
@@ -1021,7 +1021,8 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 						group->iommu_group,
 						group->type);
 		if (ret) {
-			if (group->type = VFIO_IOMMU)
+			if (group->type = VFIO_IOMMU &&
+			    iommu_group_dma_owner_claimed(group->iommu_group))
 				iommu_group_release_dma_owner(
 					group->iommu_group);
 			goto unlock_out;
-- 
2.30.2