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: a48ce36e2786 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Henry Willard <henry.willard@oracle.com>
Link: https://lore.kernel.org/r/20231026084942.17387-1-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 3bfc56d..c146378 100644 (file)
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1108,7 +1108,8 @@ map_end:
 
        }
 
-       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);