vfio/migration: Allow live migration with vIOMMU without VFs using device dirty tracking

Commit e46883204c ("vfio/migration: Block migration with vIOMMU")
introduces a migration blocker when vIOMMU is enabled, because we need
to calculate the IOVA ranges for device dirty tracking. But this is
unnecessary for iommu dirty tracking.

Limit the vfio_viommu_preset() check to those devices which use device
dirty tracking. This allows live migration with VFIO devices which use
iommu dirty tracking.

Suggested-by: Jason Zeng <jason.zeng@intel.com>
Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Tested-by: Giovannio Cabiddu <giovanni.cabiddu@intel.com>
Tested-by: Rohith S R <rohith.s.r@intel.com>
Link: https://lore.kernel.org/qemu-devel/20251218062643.624796-10-zhenzhong.duan@intel.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/container.c

@@ -178,10 +178,7 @@ bool vfio_container_devices_dirty_tracking_is_supported(
     VFIODevice *vbasedev;
 
     QLIST_FOREACH(vbasedev, &bcontainer->device_list, container_next) {
-        if (vbasedev->device_dirty_page_tracking == ON_OFF_AUTO_OFF) {
-            return false;
-        }
-        if (!vbasedev->dirty_pages_supported) {
+        if (vfio_device_dirty_pages_disabled(vbasedev)) {
             return false;
         }
     }

hw/vfio/device.c

@@ -412,6 +412,12 @@ bool vfio_device_is_mdev(VFIODevice *vbasedev)
     return subsys && (strcmp(subsys, "/sys/bus/mdev") == 0);
 }
 
+bool vfio_device_dirty_pages_disabled(VFIODevice *vbasedev)
+{
+    return (!vbasedev->dirty_pages_supported ||
+            vbasedev->device_dirty_page_tracking == ON_OFF_AUTO_OFF);
+}
+
 bool vfio_device_hiod_create_and_realize(VFIODevice *vbasedev,
                                          const char *typename, Error **errp)
 {

hw/vfio/migration.c

@@ -1210,8 +1210,7 @@ bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
         return !vfio_block_migration(vbasedev, err, errp);
     }
 
-    if ((!vbasedev->dirty_pages_supported ||
-         vbasedev->device_dirty_page_tracking == ON_OFF_AUTO_OFF) &&
+    if (vfio_device_dirty_pages_disabled(vbasedev) &&
         !vbasedev->iommu_dirty_tracking) {
         if (vbasedev->enable_migration == ON_OFF_AUTO_AUTO) {
             error_setg(&err,
@@ -1236,7 +1235,8 @@ bool vfio_migration_realize(VFIODevice *vbasedev, Error **errp)
         goto out_deinit;
     }
 
-    if (vfio_viommu_preset(vbasedev)) {
+    if (!vfio_device_dirty_pages_disabled(vbasedev) &&
+        vfio_viommu_preset(vbasedev)) {
         error_setg(&err, "%s: Migration is currently not supported "
                    "with vIOMMU enabled", vbasedev->name);
         goto add_blocker;

include/hw/vfio/vfio-device.h

@@ -148,6 +148,16 @@ bool vfio_device_irq_set_signaling(VFIODevice *vbasedev, int index, int subindex
 
 void vfio_device_reset_handler(void *opaque);
 bool vfio_device_is_mdev(VFIODevice *vbasedev);
+/**
+ * vfio_device_dirty_pages_disabled: Check if device dirty tracking will be
+ * used for a VFIO device
+ *
+ * @vbasedev: The VFIODevice to transform
+ *
+ * Return: true if either @vbasedev doesn't support device dirty tracking or
+ * is forcedly disabled from command line, otherwise false.
+ */
+bool vfio_device_dirty_pages_disabled(VFIODevice *vbasedev);
 bool vfio_device_hiod_create_and_realize(VFIODevice *vbasedev,
                                          const char *typename, Error **errp);
 bool vfio_device_attach(char *name, VFIODevice *vbasedev,