[PATCH v3 08/15] vfio/common: Relax vIOMMU detection when DMA translation is off

[Joao Martins]

Relax the vIOMMU migration blocker when the underlying IOMMU reports that
DMA translation disabled. When it is disabled there will be no DMA mappings
via the vIOMMU and the guest only uses it for Interrupt Remapping.

The latter is done via the vfio_viommu_preset() return value whereby in
addition to validating that the address space is memory, we also check
whether the IOMMU MR has DMA translation on. Assume it is enabled if
there's no IOMMU MR or if no dma-translation property is supported.

Signed-off-by: Joao Martins <joao.m.mart...@oracle.com>
---
 hw/vfio/common.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index fa8fd949b1cf..060acccb3443 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -414,12 +414,32 @@ void vfio_unblock_multiple_devices_migration(void)
     multiple_devices_migration_blocker = NULL;
 }
 
+static bool vfio_viommu_dma_translation_enabled(VFIOAddressSpace *space)
+{
+    bool enabled = false;
+    int ret;
+
+    if (!space->iommu_mr) {
+        return true;
+    }
+
+    ret = memory_region_iommu_get_attr(space->iommu_mr,
+                                       IOMMU_ATTR_DMA_TRANSLATION,
+                                       &enabled);
+    if (ret || enabled) {
+        return true;
+    }
+
+    return false;
+}
+
 static bool vfio_viommu_preset(void)
 {
     VFIOAddressSpace *space;
 
     QLIST_FOREACH(space, &vfio_address_spaces, list) {
-        if (space->as != &address_space_memory) {
+        if ((space->as != &address_space_memory) &&
+            vfio_viommu_dma_translation_enabled(space)) {
             return true;
         }
     }
-- 
2.39.3