iommu: Avoid unnecessary cache invalidations

The iommu_create_device_direct_mappings() only needs to flush the caches
when the mappings are changed in the affected domain. This is not true
for non-DMA domains, or for devices attached to the domain that have no
reserved regions. To avoid unnecessary cache invalidations, add a check
before iommu_flush_iotlb_all().

Fixes: a48ce36 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
Signed-off-by: Lu Baolu <[email protected]>
Tested-by: Henry Willard <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

Author: LuBaolu

drivers/iommu/iommu.c

@@ -1108,7 +1108,8 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
 
 	}
 
-	iommu_flush_iotlb_all(domain);
+	if (!list_empty(&mappings) && iommu_is_dma_domain(domain))
+		iommu_flush_iotlb_all(domain);
 
 out:
 	iommu_put_resv_regions(dev, &mappings);