vhost: add a helper for force stopping a device

This adds an ability to skip GET_VRING_BASE during device stop entirely,
and thus the expensive drain operation that this call entails as well,
which may be useful during a non-graceful shutdown in case the guest
operating system hangs or refuses to react to a previously requested
ACPI shutdown for whatever reason.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Message-Id: <20250609212547.2859224-3-d-tatianin@yandex-team.ru>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 54 insertions, 13 deletions

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index c87861b..c30ea11 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1354,25 +1354,30 @@ fail_alloc_desc:
     return r;
 }
 
-int vhost_virtqueue_stop(struct vhost_dev *dev,
-                         struct VirtIODevice *vdev,
-                         struct vhost_virtqueue *vq,
-                         unsigned idx)
+static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
+                                   struct VirtIODevice *vdev,
+                                   struct vhost_virtqueue *vq,
+                                   unsigned idx, bool force)
 {
     int vhost_vq_index = dev->vhost_ops->vhost_get_vq_index(dev, idx);
     struct vhost_vring_state state = {
         .index = vhost_vq_index,
     };
-    int r;
+    int r = 0;
 
     if (virtio_queue_get_desc_addr(vdev, idx) == 0) {
         /* Don't stop the virtqueue which might have not been started */
         return 0;
     }
 
-    r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
-    if (r < 0) {
-        VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
+    if (!force) {
+        r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
+        if (r < 0) {
+            VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
+        }
+    }
+
+    if (r < 0 || force) {
         /* Connection to the backend is broken, so let's sync internal
          * last avail idx to the device used idx.
          */
@@ -1401,6 +1406,14 @@ int vhost_virtqueue_stop(struct vhost_dev *dev,
     return r;
 }
 
+int vhost_virtqueue_stop(struct vhost_dev *dev,
+                         struct VirtIODevice *vdev,
+                         struct vhost_virtqueue *vq,
+                         unsigned idx)
+{
+    return do_vhost_virtqueue_stop(dev, vdev, vq, idx, false);
+}
+
 static int vhost_virtqueue_set_busyloop_timeout(struct vhost_dev *dev,
                                                 int n, uint32_t timeout)
 {
@@ -2119,7 +2132,8 @@ fail_features:
 }
 
 /* Host notifiers must be enabled at this point. */
-int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
+static int do_vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev,
+                             bool vrings, bool force)
 {
     int i;
     int rc = 0;
@@ -2141,10 +2155,11 @@ int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
         vhost_dev_set_vring_enable(hdev, false);
     }
     for (i = 0; i < hdev->nvqs; ++i) {
-        rc |= vhost_virtqueue_stop(hdev,
-                                   vdev,
-                                   hdev->vqs + i,
-                                   hdev->vq_index + i);
+        rc |= do_vhost_virtqueue_stop(hdev,
+                                      vdev,
+                                      hdev->vqs + i,
+                                      hdev->vq_index + i,
+                                      force);
     }
     if (hdev->vhost_ops->vhost_reset_status) {
         hdev->vhost_ops->vhost_reset_status(hdev);
@@ -2164,6 +2179,17 @@ int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
     return rc;
 }
 
+int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
+{
+    return do_vhost_dev_stop(hdev, vdev, vrings, false);
+}
+
+int vhost_dev_force_stop(struct vhost_dev *hdev, VirtIODevice *vdev,
+                         bool vrings)
+{
+    return do_vhost_dev_stop(hdev, vdev, vrings, true);
+}
+
 int vhost_net_set_backend(struct vhost_dev *hdev,
                           struct vhost_vring_file *file)
 {
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 38800a7..eb3dd76 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -238,6 +238,21 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings);
 int vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings);
 
 /**
+ * vhost_dev_force_stop() - force stop the vhost device
+ * @hdev: common vhost_dev structure
+ * @vdev: the VirtIODevice structure
+ * @vrings: true to have vrings disabled in this call
+ *
+ * Force stop the vhost device. After the device is stopped the notifiers
+ * can be disabled (@vhost_dev_disable_notifiers) and the device can
+ * be torn down (@vhost_dev_cleanup). Unlike @vhost_dev_stop, this doesn't
+ * attempt to flush in-flight backend requests by skipping GET_VRING_BASE
+ * entirely.
+ */
+int vhost_dev_force_stop(struct vhost_dev *hdev, VirtIODevice *vdev,
+                         bool vrings);
+
+/**
  * DOC: vhost device configuration handling
  *
  * The VirtIO device configuration space is used for rarely changing