migration: add migration capability to bypass the shared memory

Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>

exec.c

@@ -1334,6 +1334,11 @@ static RAMBlock *find_ram_block(ram_addr_t addr)
     return NULL;
 }
 
+bool qemu_ram_is_shared(RAMBlock *rb)
+{
+    return rb->flags & RAM_SHARED;
+}
+
 /* Called with iothread lock held.  */
 void qemu_ram_set_idstr(ram_addr_t addr, const char *name, DeviceState *dev)
 {

include/exec/cpu-all.h

@@ -300,6 +300,8 @@ static inline void *ramblock_ptr(RAMBlock *block, ram_addr_t offset)
     return (char *)block->host + offset;
 }
 
+bool qemu_ram_is_shared(RAMBlock *rb);
+
 typedef struct RAMList {
     QemuMutex mutex;
     /* Protected by the iothread lock.  */

include/migration/migration.h

@@ -178,6 +178,7 @@ int migrate_compress_level(void);
 int migrate_compress_threads(void);
 int migrate_decompress_threads(void);
 bool migrate_use_events(void);
+bool migrate_bypass_shared_memory(void);
 
 void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
 void ram_control_after_iterate(QEMUFile *f, uint64_t flags);

migration/migration.c

@@ -227,6 +227,15 @@ static void migrate_generate_event(int new_state)
     }
 }
 
+bool migrate_bypass_shared_memory(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_BYPASS_SHARED_MEMORY];
+}
+
 /*
  * Called on -incoming with a defer: uri.
  * The migration can be started later after any parameters have been

migration/ram.c

@@ -546,6 +546,28 @@ static void migration_bitmap_sync_init(void)
     num_dirty_pages_period = 0;
     xbzrle_cache_miss_prev = 0;
     iterations_prev = 0;
+    migration_dirty_pages = 0;
+}
+
+static void migration_bitmap_init(unsigned long *bitmap)
+{
+    RAMBlock *block;
+
+    bitmap_clear(bitmap, 0, last_ram_offset() >> TARGET_PAGE_BITS);
+    rcu_read_lock();
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        if (!migrate_bypass_shared_memory() || !qemu_ram_is_shared(block)) {
+            bitmap_set(bitmap, block->offset >> TARGET_PAGE_BITS,
+                       block->used_length >> TARGET_PAGE_BITS);
+
+            /*
+             * Count the total number of pages used by ram blocks not including
+             * any gaps due to alignment or unplugs.
+             */
+	    migration_dirty_pages += block->used_length >> TARGET_PAGE_BITS;
+	}
+    }
+    rcu_read_unlock();
 }
 
 /* Called with iothread lock held, to protect ram_list.dirty_memory[] */
@@ -573,7 +595,9 @@ static void migration_bitmap_sync(void)
     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);
+        if (!migrate_bypass_shared_memory() || !qemu_ram_is_shared(block)) {
+            migration_bitmap_sync_range(block->offset, block->used_length);
+        }
     }
     rcu_read_unlock();
     qemu_mutex_unlock(&migration_bitmap_mutex);
@@ -1147,12 +1171,7 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
     migration_bitmap = bitmap_new(ram_bitmap_pages);
     bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
-
-    /*
-     * Count the total number of pages used by ram blocks not including any
-     * gaps due to alignment or unplugs.
-     */
-    migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
+    migration_bitmap_init(migration_bitmap);
 
     memory_global_dirty_log_start();
     migration_bitmap_sync();

qapi-schema.json

@@ -529,11 +529,15 @@
 # @auto-converge: If enabled, QEMU will automatically throttle down the guest
 #          to speed up convergence of RAM migration. (since 1.6)
 #
+# @bypass-shared-memory: the shared memory region will be bypassed on migration.
+#          This feature allows the memory region to be reused by new qemu(s)
+#          or be migrated separately. (since 2.6)
+#
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
   'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
-           'compress', 'events'] }
+           'compress', 'events', 'bypass-shared-memory'] }
 
 ##
 # @MigrationCapabilityStatus

qmp-commands.hx

@@ -3407,6 +3407,7 @@ Enable/Disable migration capabilities
 - "auto-converge": throttle down guest to help convergence of migration
 - "zero-blocks": compress zero blocks during block migration
 - "events": generate events for each migration state change
+- "bypass-shared-memory": bypass shared memory region
 
 Arguments:
 
@@ -3434,6 +3435,7 @@ Query current migration capabilities
          - "rdma-pin-all" : RDMA Pin Page state (json-bool)
          - "auto-converge" : Auto Converge state (json-bool)
          - "zero-blocks" : Zero Blocks state (json-bool)
+         - "bypass-shared-memory": bypass shared memory state (json-bool)
 
 Arguments: