[PATCH 3/8] migration: support to detect compression and decompression errors

[guangrong.xiao@gmail.com]

From: Xiao Guangrong <xiaoguangrong@tencent.com>

Currently the page being compressed is allowed to be updated by
the VM on the source QEMU, correspondingly the destination QEMU
just ignores the decompression error. However, we completely miss
the chance to catch real errors, then the VM is corrupted silently

To make the migration more robuster, we copy the page to a buffer
first to avoid it being written by VM, then detect and handle the
errors of both compression and decompression errors properly

Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
---
 migration/qemu-file.c |  4 ++--
 migration/ram.c       | 29 +++++++++++++++++++----------
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 1ff33a1ffb..137bcc8bdc 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -711,9 +711,9 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_stream *stream,
     blen = qemu_compress_data(stream, f->buf + f->buf_index + sizeof(int32_t),
                               blen, p, size);
     if (blen < 0) {
-        error_report("Compress Failed!");
-        return 0;
+        return -1;
     }
+
     qemu_put_be32(f, blen);
     if (f->ops->writev_buffer) {
         add_to_iovec(f, f->buf + f->buf_index, blen, false);
diff --git a/migration/ram.c b/migration/ram.c
index fff3f31e90..c47185d38c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -273,6 +273,7 @@ struct DecompressParam {
     bool quit;
     QemuMutex mutex;
     QemuCond cond;
+    QEMUFile *file;
     void *des;
     uint8_t *compbuf;
     int len;
@@ -1051,11 +1052,13 @@ static int do_compress_ram_page(QEMUFile *f, z_stream *stream, RAMBlock *block,
 {
     RAMState *rs = ram_state;
     int bytes_sent, blen;
-    uint8_t *p = block->host + (offset & TARGET_PAGE_MASK);
+    uint8_t buf[TARGET_PAGE_SIZE], *p;
 
+    p = block->host + (offset & TARGET_PAGE_MASK);
     bytes_sent = save_page_header(rs, f, block, offset |
                                   RAM_SAVE_FLAG_COMPRESS_PAGE);
-    blen = qemu_put_compression_data(f, stream, p, TARGET_PAGE_SIZE);
+    memcpy(buf, p, TARGET_PAGE_SIZE);
+    blen = qemu_put_compression_data(f, stream, buf, TARGET_PAGE_SIZE);
     if (blen < 0) {
         bytes_sent = 0;
         qemu_file_set_error(migrate_get_current()->to_dst_file, blen);
@@ -2547,7 +2550,7 @@ static void *do_data_decompress(void *opaque)
     DecompressParam *param = opaque;
     unsigned long pagesize;
     uint8_t *des;
-    int len;
+    int len, ret;
 
     qemu_mutex_lock(&param->mutex);
     while (!param->quit) {
@@ -2563,8 +2566,12 @@ static void *do_data_decompress(void *opaque)
              * not a problem because the dirty page will be retransferred
              * and uncompress() won't break the data in other pages.
              */
-            qemu_uncompress(&param->stream, des, pagesize,
-                            param->compbuf, len);
+            ret = qemu_uncompress(&param->stream, des, pagesize,
+                                  param->compbuf, len);
+            if (ret < 0) {
+                error_report("decompress data failed");
+                qemu_file_set_error(param->file, ret);
+            }
 
             qemu_mutex_lock(&decomp_done_lock);
             param->done = true;
@@ -2581,12 +2588,12 @@ static void *do_data_decompress(void *opaque)
     return NULL;
 }
 
-static void wait_for_decompress_done(void)
+static int wait_for_decompress_done(QEMUFile *f)
 {
     int idx, thread_count;
 
     if (!migrate_use_compression()) {
-        return;
+        return 0;
     }
 
     thread_count = migrate_decompress_threads();
@@ -2597,6 +2604,7 @@ static void wait_for_decompress_done(void)
         }
     }
     qemu_mutex_unlock(&decomp_done_lock);
+    return qemu_file_get_error(f);
 }
 
 static void compress_threads_load_cleanup(void)
@@ -2635,7 +2643,7 @@ static void compress_threads_load_cleanup(void)
     decomp_param = NULL;
 }
 
-static int compress_threads_load_setup(void)
+static int compress_threads_load_setup(QEMUFile *f)
 {
     int i, thread_count;
 
@@ -2654,6 +2662,7 @@ static int compress_threads_load_setup(void)
         }
         decomp_param[i].stream.opaque = &decomp_param[i];
 
+        decomp_param[i].file = f;
         qemu_mutex_init(&decomp_param[i].mutex);
         qemu_cond_init(&decomp_param[i].cond);
         decomp_param[i].compbuf = g_malloc0(compressBound(TARGET_PAGE_SIZE));
@@ -2708,7 +2717,7 @@ static void decompress_data_with_multi_threads(QEMUFile *f,
  */
 static int ram_load_setup(QEMUFile *f, void *opaque)
 {
-    if (compress_threads_load_setup()) {
+    if (compress_threads_load_setup(f)) {
         return -1;
     }
 
@@ -3063,7 +3072,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
         }
     }
 
-    wait_for_decompress_done();
+    ret |= wait_for_decompress_done(f);
     rcu_read_unlock();
     trace_ram_load_complete(ret, seq_iter);
     return ret;
-- 
2.14.3