[Qemu-devel] [RFC/PATCH] migration: SMRAM dirty bitmap not fetched from kvm-kmod and not send to destination

["Herongguang (Stephen)" <herongguang.he@huawei.com>]

Hi,
We found a problem that when a redhat 6 VM reboots (in grub countdown UI), migrating this VM will result in VM’s memory difference between source and destination side. The difference always resides in GPA 0xA0000~0xC0000, i.e. SMRAM area.

Occasionally this result in VM instruction emulation error in destination side.

After some digging, I think this is because in migration code, in migration_bitmap_sync(), only memory slots in address space address_space_memory’s dirty bitmap  fetched from kvm-kmod, while SMRAM memory slot, in address space smram_address_space’s dirty bitmap not fetched from kvm-kmod, thus modifications in SMRAM in source side are not sent to destination side.

I tried following patch, and this phenomenon does not happen anymore. Do you think this patch is OK or do you have better idea? Thanks.

diff --git a/migration/ram.c b/migration/ram.c
index a3d70c4..1cc4360 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -607,6 +607,8 @@ static void migration_bitmap_sync_init(void)
      iterations_prev = 0;
  }

+extern AddressSpace smram_address_space;
+
  static void migration_bitmap_sync(void)
  {
      RAMBlock *block;
@@ -627,6 +629,7 @@ static void migration_bitmap_sync(void)

      trace_migration_bitmap_sync_start();
      address_space_sync_dirty_bitmap(&address_space_memory);
+    address_space_sync_dirty_bitmap(&smram_address_space);

      qemu_mutex_lock(&migration_bitmap_mutex);
      rcu_read_lock();
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index d1a25c5..b98fe22 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -1111,7 +1111,7 @@ static int kvm_get_supported_msrs(KVMState *s)

  static Notifier smram_machine_done;
  static KVMMemoryListener smram_listener;
-static AddressSpace smram_address_space;
+AddressSpace smram_address_space;
  static MemoryRegion smram_as_root;
  static MemoryRegion smram_as_mem;