memory: Allow replay of IOMMU mapping notifications

When we have guest visible IOMMUs, we allow notifiers to be registered
which will be informed of all changes to IOMMU mappings.  This is used by
vfio to keep the host IOMMU mappings in sync with guest IOMMU mappings.

However, unlike with a memory region listener, an iommu notifier won't be
told about any mappings which already exist in the (guest) IOMMU at the
time it is registered.  This can cause problems if hotplugging a VFIO
device onto a guest bus which had existing guest IOMMU mappings, but didn't
previously have an VFIO devices (and hence no host IOMMU mappings).

This adds a memory_region_iommu_replay() function to handle this case.  It
replays any existing mappings in an IOMMU memory region to a specified
notifier.  Because the IOMMU memory region doesn't internally remember the
granularity of the guest IOMMU it has a small hack where the caller must
specify a granularity at which to replay mappings.

If there are finer mappings in the guest IOMMU these will be reported in
the iotlb structures passed to the notifier which it must handle (probably
causing it to flag an error).  This isn't new - the VFIO iommu notifier
must already handle notifications about guest IOMMU mappings too short
for it to represent in the host IOMMU.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

2 files changed, 33 insertions, 0 deletions

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 5baaf48234..0f07159bb4 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -583,6 +583,19 @@ void memory_region_notify_iommu(MemoryRegion *mr,
 void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n);
 
 /**
+ * memory_region_iommu_replay: replay existing IOMMU translations to
+ * a notifier
+ *
+ * @mr: the memory region to observe
+ * @n: the notifier to which to replay iommu mappings
+ * @granularity: Minimum page granularity to replay notifications for
+ * @is_write: Whether to treat the replay as a translate "write"
+ *     through the iommu
+ */
+void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n,
+                                hwaddr granularity, bool is_write);
+
+/**
  * memory_region_unregister_iommu_notifier: unregister a notifier for
  * changes to IOMMU translation entries.
  *
diff --git a/memory.c b/memory.c
index ef87363067..1b03d2251c 100644
--- a/memory.c
+++ b/memory.c
@@ -1403,6 +1403,26 @@ void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n)
     notifier_list_add(&mr->iommu_notify, n);
 }
 
+void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n,
+                                hwaddr granularity, bool is_write)
+{
+    hwaddr addr;
+    IOMMUTLBEntry iotlb;
+
+    for (addr = 0; addr < memory_region_size(mr); addr += granularity) {
+        iotlb = mr->iommu_ops->translate(mr, addr, is_write);
+        if (iotlb.perm != IOMMU_NONE) {
+            n->notify(n, &iotlb);
+        }
+
+        /* if (2^64 - MR size) < granularity, it's possible to get an
+         * infinite loop here.  This should catch such a wraparound */
+        if ((addr + granularity) < addr) {
+            break;
+        }
+    }
+}
+
 void memory_region_unregister_iommu_notifier(Notifier *n)
 {
     notifier_remove(n);