[Qemu-devel] [PATCH 6/7] vfio: Allow hotplug of containers onto existing guest IOMMU mappings

[David Gibson <david@gibson.dropbear.id.au>]

At present the memory listener used by vfio to keep host IOMMU mappings
in sync with the guest memory image assumes that if a guest IOMMU
appears, then it has no existing mappings.

This may not be true if a VFIO device is hotplugged onto a guest bus
which didn't previously include a VFIO device, and which has existing
guest IOMMU mappings.

Therefore, use the memory_region_register_iommu_notifier_replay()
function in order to fix this case, replaying existing guest IOMMU
mappings, bringing the host IOMMU into sync with the guest IOMMU.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/vfio/common.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index db8dff3..8a4fba9 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -312,6 +312,11 @@ out:
     rcu_read_unlock();
 }
 
+static hwaddr vfio_container_granularity(VFIOContainer *container)
+{
+    return (hwaddr)1 << ctz64(container->iova_pgsizes);
+}
+
 static void vfio_listener_region_add(MemoryListener *listener,
                                      MemoryRegionSection *section)
 {
@@ -369,26 +374,14 @@ static void vfio_listener_region_add(MemoryListener *listener,
          * would be the right place to wire that up (tell the KVM
          * device emulation the VFIO iommu handles to use).
          */
-        /*
-         * This assumes that the guest IOMMU is empty of
-         * mappings at this point.
-         *
-         * One way of doing this is:
-         * 1. Avoid sharing IOMMUs between emulated devices or different
-         * IOMMU groups.
-         * 2. Implement VFIO_IOMMU_ENABLE in the host kernel to fail if
-         * there are some mappings in IOMMU.
-         *
-         * VFIO on SPAPR does that. Other IOMMU models may do that different,
-         * they must make sure there are no existing mappings or
-         * loop through existing mappings to map them into VFIO.
-         */
         giommu = g_malloc0(sizeof(*giommu));
         giommu->iommu = section->mr;
         giommu->container = container;
         giommu->n.notify = vfio_iommu_map_notify;
         QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
-        memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
+
+        memory_region_register_iommu_notifier_replay(giommu->iommu, &giommu->n,
+            vfio_container_granularity(container), false);
 
         return;
     }
-- 
2.4.3