[PATCH v8 04/13] vfio/migration: Allow migration without VFIO IOMMU dirty tracking support

[Avihai Horon]

Currently, if IOMMU of a VFIO container doesn't support dirty page
tracking, migration is blocked. This is because a DMA-able VFIO device
can dirty RAM pages without updating QEMU about it, thus breaking the
migration.

However, this doesn't mean that migration can't be done at all.
In such case, allow migration and let QEMU VFIO code mark all pages
dirty.

This guarantees that all pages that might have gotten dirty are reported
back, and thus guarantees a valid migration even without VFIO IOMMU
dirty tracking support.

The motivation for this patch is the introduction of iommufd [1].
iommufd can directly implement the /dev/vfio/vfio container IOCTLs by
mapping them into its internal ops, allowing the usage of these IOCTLs
over iommufd. However, VFIO IOMMU dirty tracking is not supported by
this VFIO compatibility API.

This patch will allow migration by hosts that use the VFIO compatibility
API and prevent migration regressions caused by the lack of VFIO IOMMU
dirty tracking support.

[1]
https://lore.kernel.org/kvm/0-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com/

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
---
 hw/vfio/common.c    | 20 ++++++++++++++++++--
 hw/vfio/migration.c |  3 +--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 130e5d1dc7..f6dd571549 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -488,6 +488,12 @@ static int vfio_dma_unmap(VFIOContainer *container,
         return -errno;
     }
 
+    if (iotlb && vfio_devices_all_running_and_saving(container)) {
+        cpu_physical_memory_set_dirty_range(iotlb->translated_addr, size,
+                                            tcg_enabled() ? DIRTY_CLIENTS_ALL :
+                                            DIRTY_CLIENTS_NOCODE);
+    }
+
     return 0;
 }
 
@@ -1201,6 +1207,10 @@ static void vfio_set_dirty_page_tracking(VFIOContainer 
*container, bool start)
         .argsz = sizeof(dirty),
     };
 
+    if (!container->dirty_pages_supported) {
+        return;
+    }
+
     if (start) {
         dirty.flags = VFIO_IOMMU_DIRTY_PAGES_FLAG_START;
     } else {
@@ -1236,6 +1246,13 @@ static int vfio_get_dirty_bitmap(VFIOContainer 
*container, uint64_t iova,
     uint64_t pages;
     int ret;
 
+    if (!container->dirty_pages_supported) {
+        cpu_physical_memory_set_dirty_range(ram_addr, size,
+                                            tcg_enabled() ? DIRTY_CLIENTS_ALL :
+                                            DIRTY_CLIENTS_NOCODE);
+        return 0;
+    }
+
     dbitmap = g_malloc0(sizeof(*dbitmap) + sizeof(*range));
 
     dbitmap->argsz = sizeof(*dbitmap) + sizeof(*range);
@@ -1409,8 +1426,7 @@ static void vfio_listener_log_sync(MemoryListener 
*listener,
 {
     VFIOContainer *container = container_of(listener, VFIOContainer, listener);
 
-    if (vfio_listener_skipped_section(section) ||
-        !container->dirty_pages_supported) {
+    if (vfio_listener_skipped_section(section)) {
         return;
     }
 
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 09fe7c1de2..552c2313b2 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -860,11 +860,10 @@ int64_t vfio_mig_bytes_transferred(void)
 
 int vfio_migration_probe(VFIODevice *vbasedev, Error **errp)
 {
-    VFIOContainer *container = vbasedev->group->container;
     struct vfio_region_info *info = NULL;
     int ret = -ENOTSUP;
 
-    if (!vbasedev->enable_migration || !container->dirty_pages_supported) {
+    if (!vbasedev->enable_migration) {
         goto add_blocker;
     }
 
-- 
2.26.3