[PATCH v2 1/2] vhost-user: fix VirtQ notifier cleanup

[Xueming Li]

When vhost-user device stop and unmmap notifier address, vCPU thread
that writing the notifier via old flatview failed with accessing invalid
address.

To avoid this concurrent issue, wait memory flatview update by draining
rcu callbacks before unmaping notifiers.

Fixes: 44866521bd6e ("vhost-user: support registering external host notifiers")
Cc: tiwei....@intel.com
Cc: qemu-sta...@nongnu.org
Cc: Yuwei Zhang <zhangyuwei.9...@bytedance.com>
Signed-off-by: Xueming Li <xuemi...@nvidia.com>
---
 hw/virtio/vhost-user.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 2c8556237f..08581e6711 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1165,6 +1165,11 @@ static void vhost_user_host_notifier_remove(struct 
vhost_dev *dev,
 
     if (n->addr && n->set) {
         virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
+        if (!qemu_in_vcpu_thread())
+            /* Wait vCPU threads accessing notifier via old flatview. */
+            drain_call_rcu();
+        munmap(n->addr, qemu_real_host_page_size);
+        n->addr = NULL;
         n->set = false;
     }
 }
@@ -1502,12 +1507,7 @@ static int 
vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
 
     n = &user->notifier[queue_idx];
 
-    if (n->addr) {
-        virtio_queue_set_host_notifier_mr(vdev, queue_idx, &n->mr, false);
-        object_unparent(OBJECT(&n->mr));
-        munmap(n->addr, page_size);
-        n->addr = NULL;
-    }
+    vhost_user_host_notifier_remove(dev, queue_idx);
 
     if (area->u64 & VHOST_USER_VRING_NOFD_MASK) {
         return 0;
@@ -2484,11 +2484,17 @@ void vhost_user_cleanup(VhostUserState *user)
     for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
         if (user->notifier[i].addr) {
             object_unparent(OBJECT(&user->notifier[i].mr));
+        }
+    }
+    memory_region_transaction_commit();
+    /* Wait VM threads accessing old flatview which contains notifier. */
+    drain_call_rcu();
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        if (user->notifier[i].addr) {
             munmap(user->notifier[i].addr, qemu_real_host_page_size);
             user->notifier[i].addr = NULL;
         }
     }
-    memory_region_transaction_commit();
     user->chr = NULL;
 }
 
-- 
2.33.0