[Qemu-devel] [PATCH 07/15] COLO: Load PVM's dirty pages into SVM's RAM cache temporarily

[zhanghailiang]

We should not load PVM's state directly into SVM, because there maybe some
errors happen when SVM is receving data, which will break SVM.

We need to ensure receving all data before load the state into SVM. We use
an extra memory to cache these data (PVM's ram). The ram cache in secondary side
is initially the same as SVM/PVM's memory. And in the process of checkpoint,
we cache the dirty pages of PVM into this ram cache firstly, so this ram cache
always the same as PVM's memory at every checkpoint, then we flush this cached 
ram
to SVM after we receive all PVM's state.

Cc: Juan Quintela <address@hidden>
Signed-off-by: zhanghailiang <address@hidden>
Signed-off-by: Li Zhijian <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
---
 include/exec/ram_addr.h       |  1 +
 include/migration/migration.h |  4 +++
 migration/colo.c              | 14 +++++++++
 migration/ram.c               | 73 ++++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 91 insertions(+), 1 deletion(-)

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 3e79466..44e1190 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -27,6 +27,7 @@ struct RAMBlock {
     struct rcu_head rcu;
     struct MemoryRegion *mr;
     uint8_t *host;
+    uint8_t *colo_cache; /* For colo, VM's ram cache */
     ram_addr_t offset;
     ram_addr_t used_length;
     ram_addr_t max_length;
diff --git a/include/migration/migration.h b/include/migration/migration.h
index 1735d66..93c6148 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -379,4 +379,8 @@ int ram_save_queue_pages(MigrationState *ms, const char 
*rbname,
 PostcopyState postcopy_state_get(void);
 /* Set the state and return the old state */
 PostcopyState postcopy_state_set(PostcopyState new_state);
+
+/* ram cache */
+int colo_init_ram_cache(void);
+void colo_release_ram_cache(void);
 #endif
diff --git a/migration/colo.c b/migration/colo.c
index 1e3e975..edb7f00 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -551,6 +551,7 @@ void *colo_process_incoming_thread(void *opaque)
     uint64_t total_size;
     uint64_t value;
     Error *local_err = NULL;
+    int ret;
 
     qemu_sem_init(&mis->colo_incoming_sem, 0);
 
@@ -572,6 +573,12 @@ void *colo_process_incoming_thread(void *opaque)
      */
     qemu_file_set_blocking(mis->from_src_file, true);
 
+    ret = colo_init_ram_cache();
+    if (ret < 0) {
+        error_report("Failed to initialize ram cache");
+        goto out;
+    }
+
     bioc = qio_channel_buffer_new(COLO_BUFFER_BASE_SIZE);
     fb = qemu_fopen_channel_input(QIO_CHANNEL(bioc));
     object_unref(OBJECT(bioc));
@@ -705,11 +712,18 @@ out:
     if (fb) {
         qemu_fclose(fb);
     }
+    /*
+     * We can ensure BH is hold the global lock, and will join COLO
+     * incoming thread, so here it is not necessary to lock here again,
+     * Or there will be a deadlock error.
+     */
+    colo_release_ram_cache();
 
     /* Hope this not to be too long to loop here */
     qemu_sem_wait(&mis->colo_incoming_sem);
     qemu_sem_destroy(&mis->colo_incoming_sem);
     /* Must be called after failover BH is completed */
+
     if (mis->to_src_file) {
         qemu_fclose(mis->to_src_file);
     }
diff --git a/migration/ram.c b/migration/ram.c
index f289fcd..b588990 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -219,6 +219,7 @@ static RAMBlock *last_sent_block;
 static ram_addr_t last_offset;
 static QemuMutex migration_bitmap_mutex;
 static uint64_t migration_dirty_pages;
+static bool ram_cache_enable;
 static uint32_t last_version;
 static bool ram_bulk_stage;
 
@@ -2227,6 +2228,20 @@ static inline void *host_from_ram_block_offset(RAMBlock 
*block,
     return block->host + offset;
 }
 
+static inline void *colo_cache_from_block_offset(RAMBlock *block,
+                                                 ram_addr_t offset)
+{
+    if (!offset_in_ramblock(block, offset)) {
+        return NULL;
+    }
+    if (!block->colo_cache) {
+        error_report("%s: colo_cache is NULL in block :%s",
+                     __func__, block->idstr);
+        return NULL;
+    }
+    return block->colo_cache + offset;
+}
+
 /*
  * If a page (or a whole RDMA chunk) has been
  * determined to be zero, then zap it.
@@ -2542,7 +2557,12 @@ static int ram_load(QEMUFile *f, void *opaque, int 
version_id)
                      RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
             RAMBlock *block = ram_block_from_stream(f, flags);
 
-            host = host_from_ram_block_offset(block, addr);
+            /* After going into COLO, we should load the Page into colo_cache 
*/
+            if (ram_cache_enable) {
+                host = colo_cache_from_block_offset(block, addr);
+            } else {
+                host = host_from_ram_block_offset(block, addr);
+            }
             if (!host) {
                 error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
                 ret = -EINVAL;
@@ -2637,6 +2657,57 @@ static int ram_load(QEMUFile *f, void *opaque, int 
version_id)
     return ret;
 }
 
+/*
+ * colo cache: this is for secondary VM, we cache the whole
+ * memory of the secondary VM, it will be called after first migration.
+ */
+int colo_init_ram_cache(void)
+{
+    RAMBlock *block;
+
+    rcu_read_lock();
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        block->colo_cache = qemu_anon_ram_alloc(block->used_length, NULL);
+        if (!block->colo_cache) {
+            error_report("%s: Can't alloc memory for COLO cache of block %s,"
+                         "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
+                         block->used_length);
+            goto out_locked;
+        }
+        memcpy(block->colo_cache, block->host, block->used_length);
+    }
+    rcu_read_unlock();
+    ram_cache_enable = true;
+    return 0;
+
+out_locked:
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        if (block->colo_cache) {
+            qemu_anon_ram_free(block->colo_cache, block->used_length);
+            block->colo_cache = NULL;
+        }
+    }
+
+    rcu_read_unlock();
+    return -errno;
+}
+
+void colo_release_ram_cache(void)
+{
+    RAMBlock *block;
+
+    ram_cache_enable = false;
+
+    rcu_read_lock();
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        if (block->colo_cache) {
+            qemu_anon_ram_free(block->colo_cache, block->used_length);
+            block->colo_cache = NULL;
+        }
+    }
+    rcu_read_unlock();
+}
+
 static SaveVMHandlers savevm_ram_handlers = {
     .save_live_setup = ram_save_setup,
     .save_live_iterate = ram_save_iterate,
-- 
1.8.3.1