[Qemu-devel] [PATCH] virtio/vhost: reset dev->log after syncing

[Felipe Franciosi <felipe@nutanix.com>]

vhost_log_put() is called to decomission the dirty log between qemu and
a vhost device when stopping the device. Such a call can happen from
migration_completion().

Present code sets dev->log_size to zero too early in vhost_log_put(),
causing the sync check to always return false. As a consequence, the
last pass on the dirty bitmap never happens at the end of migration.

If a vhost device was busy (writing to guest memory) until the last
moments before vhost_virtqueue_stop(), this error will result in guest
memory corruption (at least) following migrations.

Signed-off-by: Felipe Franciosi <felipe@nutanix.com>
---
 hw/virtio/vhost.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 5fd69f0..ddc42f0 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -375,8 +375,6 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
     if (!log) {
         return;
     }
-    dev->log = NULL;
-    dev->log_size = 0;
 
     --log->refcnt;
     if (log->refcnt == 0) {
@@ -396,6 +394,9 @@ static void vhost_log_put(struct vhost_dev *dev, bool sync)
 
         g_free(log);
     }
+
+    dev->log = NULL;
+    dev->log_size = 0;
 }
 
 static bool vhost_dev_log_is_shared(struct vhost_dev *dev)
-- 
1.7.1