vfio/container: Add dirty tracking started flag

Add a flag to VFIOContainerBase that indicates whether dirty tracking
has been started for the container or not.

This will be used in the following patches to allow dirty page syncs
only if dirty tracking has been started.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Tested-by: Joao Martins <joao.m.martins@oracle.com>
Link: https://lore.kernel.org/r/20241218134022.21264-2-avihaih@nvidia.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/container-base.c

@@ -64,13 +64,23 @@ int vfio_container_set_dirty_page_tracking(VFIOContainerBase *bcontainer,
                                            bool start, Error **errp)
 {
     VFIOIOMMUClass *vioc = VFIO_IOMMU_GET_CLASS(bcontainer);
+    int ret;
 
     if (!bcontainer->dirty_pages_supported) {
         return 0;
     }
 
     g_assert(vioc->set_dirty_page_tracking);
-    return vioc->set_dirty_page_tracking(bcontainer, start, errp);
+    if (bcontainer->dirty_pages_started == start) {
+        return 0;
+    }
+
+    ret = vioc->set_dirty_page_tracking(bcontainer, start, errp);
+    if (!ret) {
+        bcontainer->dirty_pages_started = start;
+    }
+
+    return ret;
 }
 
 int vfio_container_query_dirty_bitmap(const VFIOContainerBase *bcontainer,

include/hw/vfio/vfio-container-base.h

@@ -44,6 +44,7 @@ typedef struct VFIOContainerBase {
     unsigned long pgsizes;
     unsigned int dma_max_mappings;
     bool dirty_pages_supported;
+    bool dirty_pages_started; /* Protected by BQL */
     QLIST_HEAD(, VFIOGuestIOMMU) giommu_list;
     QLIST_HEAD(, VFIORamDiscardListener) vrdl_list;
     QLIST_ENTRY(VFIOContainerBase) next;