[Qemu-devel] [PATCHv3 4/6] virtio-net: stop/start bh when appropriate

["Michael S. Tsirkin" <mst@redhat.com>]

Avoid sending out packets, and modifying
device state, when VM is stopped.
Add assert statements to verify this does not happen.

Avoid scheduling bh when vhost-net is started.

Stop bh when driver disabled bus mastering
(we must not access memory after this).

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

---

Respinning just this one patch:
virtio-net: stop/start bh on vm start/stop

it turns out under kvm vcpu can be running after vm stop
notifier callbacks are done. And it makes sense: vcpu is
just another device, so we should not
depend on the order of vmstate notifiers.
The state callback is thus a request for device to avoid changing state
of other devices, not a guarantee that other devices
will not send requests to it.

diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index 43a2b3d..260433f 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -99,7 +99,13 @@ static void virtio_net_set_config(VirtIODevice *vdev, const uint8_t *config)
     }
 }
 
-static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
+bool virtio_net_started(VirtIONet *n, uint8_t status)
+{
+    return (status & VIRTIO_CONFIG_S_DRIVER_OK) &&
+        (n->status & VIRTIO_NET_S_LINK_UP) && n->vm_running;
+}
+
+static void virtio_net_vhost_status(struct VirtIODevice *vdev, uint8_t status)
 {
     VirtIONet *n = to_virtio_net(vdev);
     if (!n->nic->nc.peer) {
@@ -112,9 +118,7 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
     if (!tap_get_vhost_net(n->nic->nc.peer)) {
         return;
     }
-    if (!!n->vhost_started == ((status & VIRTIO_CONFIG_S_DRIVER_OK) &&
-                               (n->status & VIRTIO_NET_S_LINK_UP) &&
-                               n->vm_running)) {
+    if (!!n->vhost_started == virtio_net_started(n, status)) {
         return;
     }
     if (!n->vhost_started) {
@@ -131,6 +135,30 @@ static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
     }
 }
 
+static void virtio_net_set_status(struct VirtIODevice *vdev, uint8_t status)
+{
+    virtio_net_vhost_status(vdev, status);
+
+    if (!n->tx_waiting) {
+        return;
+    }
+
+    if (virtio_net_started(n, status) && !n->vhost_started) {
+        if (n->tx_timer) {
+            qemu_mod_timer(n->tx_timer,
+                           qemu_get_clock(vm_clock) + n->tx_timeout);
+        } else {
+            qemu_bh_schedule(n->tx_bh);
+        }
+    } else {
+        if (n->tx_timer) {
+            qemu_del_timer(n->tx_timer);
+        } else {
+            qemu_bh_cancel(n->tx_bh);
+        }
+    }
+}
+
 static void virtio_net_set_link_status(VLANClientState *nc)
 {
     VirtIONet *n = DO_UPCAST(NICState, nc, nc)->opaque;
@@ -675,11 +703,13 @@ static int32_t virtio_net_flush_tx(VirtIONet *n, VirtQueue *vq)
 {
     VirtQueueElement elem;
     int32_t num_packets = 0;
 
     if (!(n->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK)) {
         return num_packets;
     }
 
+    assert(n->vm_running);
+
     if (n->async_tx.elem.out_num) {
         virtio_queue_set_notification(n->tx_vq, 0);
         return num_packets;
@@ -738,6 +767,12 @@ static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIONet *n = to_virtio_net(vdev);
 
+    /* This happens when device was stopped but VCPU wasn't. */
+    if (!n->vm_running) {
+        n->tx_waiting = 1;
+        return;
+    }
+
     if (n->tx_waiting) {
         virtio_queue_set_notification(vq, 1);
         qemu_del_timer(n->tx_timer);
@@ -758,14 +793,19 @@ static void virtio_net_handle_tx_bh(VirtIODevice *vdev, VirtQueue *vq)
     if (unlikely(n->tx_waiting)) {
         return;
     }
+    n->tx_waiting = 1;
+    /* This happens when device was stopped but VCPU wasn't. */
+    if (!n->vm_running) {
+        return;
+    }
     virtio_queue_set_notification(vq, 0);
     qemu_bh_schedule(n->tx_bh);
-    n->tx_waiting = 1;
 }
 
 static void virtio_net_tx_timer(void *opaque)
 {
     VirtIONet *n = opaque;
+    assert(n->vm_running);
 
     n->tx_waiting = 0;
 
@@ -782,6 +822,8 @@ static void virtio_net_tx_bh(void *opaque)
     VirtIONet *n = opaque;
     int32_t ret;
 
+    assert(n->vm_running);
+
     n->tx_waiting = 0;
 
     /* Just in case the driver is not ready on more */
@@ -926,15 +968,6 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
         }
     }
     n->mac_table.first_multi = i;
-
-    if (n->tx_waiting) {
-        if (n->tx_timer) {
-            qemu_mod_timer(n->tx_timer,
-                           qemu_get_clock(vm_clock) + n->tx_timeout);
-        } else {
-            qemu_bh_schedule(n->tx_bh);
-        }
-    }
     return 0;
 }