[Qemu-devel] [PULL 27/27] migration: extend migration_bitmap

[Juan Quintela <quintela@redhat.com>]

From: Li Zhijian <lizhijian@cn.fujitsu.com>

Prevously, if we hotplug a device(e.g. device_add e1000) during
migration is processing in source side, qemu will add a new ram
block but migration_bitmap is not extended.
In this case, migration_bitmap will overflow and lead qemu abort
unexpectedly.

Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 exec.c                  |  5 +++++
 include/exec/exec-all.h |  3 +++
 migration/ram.c         | 28 ++++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/exec.c b/exec.c
index f7883d2..1702544 100644
--- a/exec.c
+++ b/exec.c
@@ -1401,6 +1401,11 @@ static ram_addr_t ram_block_add(RAMBlock *new_block, Error **errp)
         }
     }

+    new_ram_size = MAX(old_ram_size,
+              (new_block->offset + new_block->max_length) >> TARGET_PAGE_BITS);
+    if (new_ram_size > old_ram_size) {
+        migration_bitmap_extend(old_ram_size, new_ram_size);
+    }
     /* Keep the list sorted from biggest to smallest block.  Unlike QTAILQ,
      * QLIST (which has an RCU-friendly variant) does not have insertion at
      * tail, so save the last element in last_block.
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 2573e8c..91ffa99 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -385,4 +385,7 @@ static inline bool cpu_can_do_io(CPUState *cpu)
     return cpu->can_do_io != 0;
 }

+#if !defined(CONFIG_USER_ONLY)
+void migration_bitmap_extend(ram_addr_t old, ram_addr_t new);
+#endif
 #endif
diff --git a/migration/ram.c b/migration/ram.c
index 9c0bcfe..c696814 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -222,6 +222,7 @@ static RAMBlock *last_seen_block;
 static RAMBlock *last_sent_block;
 static ram_addr_t last_offset;
 static unsigned long *migration_bitmap;
+static QemuMutex migration_bitmap_mutex;
 static uint64_t migration_dirty_pages;
 static uint32_t last_version;
 static bool ram_bulk_stage;
@@ -569,11 +570,13 @@ static void migration_bitmap_sync(void)
     trace_migration_bitmap_sync_start();
     address_space_sync_dirty_bitmap(&address_space_memory);

+    qemu_mutex_lock(&migration_bitmap_mutex);
     rcu_read_lock();
     QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
         migration_bitmap_sync_range(block->mr->ram_addr, block->used_length);
     }
     rcu_read_unlock();
+    qemu_mutex_unlock(&migration_bitmap_mutex);

     trace_migration_bitmap_sync_end(migration_dirty_pages
                                     - num_dirty_pages_init);
@@ -1062,6 +1065,30 @@ static void reset_ram_globals(void)

 #define MAX_WAIT 50 /* ms, half buffered_file limit */

+void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
+{
+    /* called in qemu main thread, so there is
+     * no writing race against this migration_bitmap
+     */
+    if (migration_bitmap) {
+        unsigned long *old_bitmap = migration_bitmap, *bitmap;
+        bitmap = bitmap_new(new);
+
+        /* prevent migration_bitmap content from being set bit
+         * by migration_bitmap_sync_range() at the same time.
+         * it is safe to migration if migration_bitmap is cleared bit
+         * at the same time.
+         */
+        qemu_mutex_lock(&migration_bitmap_mutex);
+        bitmap_copy(bitmap, old_bitmap, old);
+        bitmap_set(bitmap, old, new - old);
+        atomic_rcu_set(&migration_bitmap, bitmap);
+        qemu_mutex_unlock(&migration_bitmap_mutex);
+        migration_dirty_pages += new - old;
+        synchronize_rcu();
+        g_free(old_bitmap);
+    }
+}

 /* Each of ram_save_setup, ram_save_iterate and ram_save_complete has
  * long-running RCU critical section.  When rcu-reclaims in the code
@@ -1078,6 +1105,7 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     dirty_rate_high_cnt = 0;
     bitmap_sync_count = 0;
     migration_bitmap_sync_init();
+    qemu_mutex_init(&migration_bitmap_mutex);

     if (migrate_use_xbzrle()) {
         XBZRLE_cache_lock();
-- 
2.4.3