[PATCH v4 1/2] vhost-user: fix VirtQ notifier cleanup

[Xueming Li <xuemingl@nvidia.com>]

When vhost-user device cleanup and unmmap notifier address, VM cpu
thread that writing the notifier failed with accessing invalid address.

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

Fixes: 44866521bd6e ("vhost-user: support registering external host notifiers")
Cc: tiwei.bie@intel.com
Cc: qemu-stable@nongnu.org
Cc: Yuwei Zhang <zhangyuwei.9149@bytedance.com>
Signed-off-by: Xueming Li <xuemingl@nvidia.com>
---
 hw/virtio/vhost-user.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index bf6e50223c..cfca1b9adc 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -18,6 +18,7 @@
 #include "chardev/char-fe.h"
 #include "io/channel-socket.h"
 #include "sysemu/kvm.h"
+#include "sysemu/cpus.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "qemu/sockets.h"
@@ -1165,6 +1166,12 @@ 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()) { /* Avoid vCPU dead lock. */
+            /* Wait for VM threads accessing old flatview which contains notifier. */
+            drain_call_rcu();
+        }
+        munmap(n->addr, qemu_real_host_page_size);
+        n->addr = NULL;
         n->set = false;
     }
 }
@@ -1502,12 +1509,7 @@ 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;
@@ -2485,11 +2487,17 @@ 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 for 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