vdpa-dev: Fix initialisation order to restore VDUSE compatibility

VDUSE requires that virtqueues are first enabled before the DRIVER_OK
status flag is set; with the current API of the kernel module, it is
impossible to enable the opposite order in our block export code because
userspace is not notified when a virtqueue is enabled.

This requirement also mathces the normal initialisation order as done by
the generic vhost code in QEMU. However, commit 6c482547 accidentally
changed the order for vdpa-dev and broke access to VDUSE devices with
this.

This changes vdpa-dev to use the normal order again and use the standard
vhost callback .vhost_set_vring_enable for this. VDUSE devices can be
used with vdpa-dev again after this fix.

vhost_net intentionally avoided enabling the vrings for vdpa and does
this manually later while it does enable them for other vhost backends.
Reflect this in the vhost_net code and return early for vdpa, so that
the behaviour doesn't change for this device.

Cc: qemu-stable@nongnu.org
Fixes: 6c4825476a ('vdpa: move vhost_vdpa_set_vring_ready to the caller')
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20240315155949.86066-1-kwolf@redhat.com>
Reviewed-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/net/vhost_net.c

@@ -541,6 +541,16 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
     VHostNetState *net = get_vhost_net(nc);
     const VhostOps *vhost_ops = net->dev.vhost_ops;
 
+    /*
+     * vhost-vdpa network devices need to enable dataplane virtqueues after
+     * DRIVER_OK, so they can recover device state before starting dataplane.
+     * Because of that, we don't enable virtqueues here and leave it to
+     * net/vhost-vdpa.c.
+     */
+    if (nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
+        return 0;
+    }
+
     nc->vring_enable = enable;
 
     if (vhost_ops && vhost_ops->vhost_set_vring_enable) {

hw/virtio/trace-events

@@ -49,7 +49,7 @@ vhost_vdpa_set_features(void *dev, uint64_t features) "dev: %p features: 0x%"PRI
 vhost_vdpa_get_device_id(void *dev, uint32_t device_id) "dev: %p device_id %"PRIu32
 vhost_vdpa_reset_device(void *dev) "dev: %p"
 vhost_vdpa_get_vq_index(void *dev, int idx, int vq_idx) "dev: %p idx: %d vq idx: %d"
-vhost_vdpa_set_vring_ready(void *dev, unsigned i, int r) "dev: %p, idx: %u, r: %d"
+vhost_vdpa_set_vring_enable_one(void *dev, unsigned i, int enable, int r) "dev: %p, idx: %u, enable: %u, r: %d"
 vhost_vdpa_dump_config(void *dev, const char *line) "dev: %p %s"
 vhost_vdpa_set_config(void *dev, uint32_t offset, uint32_t size, uint32_t flags) "dev: %p offset: %"PRIu32" size: %"PRIu32" flags: 0x%"PRIx32
 vhost_vdpa_get_config(void *dev, void *config, uint32_t config_len) "dev: %p config: %p config_len: %"PRIu32

hw/virtio/vdpa-dev.c

@@ -253,14 +253,11 @@ static int vhost_vdpa_device_start(VirtIODevice *vdev, Error **errp)
 
     s->dev.acked_features = vdev->guest_features;
 
-    ret = vhost_dev_start(&s->dev, vdev, false);
+    ret = vhost_dev_start(&s->dev, vdev, true);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Error starting vhost");
         goto err_guest_notifiers;
     }
-    for (i = 0; i < s->dev.nvqs; ++i) {
-        vhost_vdpa_set_vring_ready(&s->vdpa, i);
-    }
     s->started = true;
 
     /*

hw/virtio/vhost-vdpa.c

@@ -896,19 +896,41 @@ static int vhost_vdpa_get_vq_index(struct vhost_dev *dev, int idx)
     return idx;
 }
 
-int vhost_vdpa_set_vring_ready(struct vhost_vdpa *v, unsigned idx)
+static int vhost_vdpa_set_vring_enable_one(struct vhost_vdpa *v, unsigned idx,
+                                           int enable)
 {
     struct vhost_dev *dev = v->dev;
     struct vhost_vring_state state = {
         .index = idx,
-        .num = 1,
+        .num = enable,
     };
     int r = vhost_vdpa_call(dev, VHOST_VDPA_SET_VRING_ENABLE, &state);
 
-    trace_vhost_vdpa_set_vring_ready(dev, idx, r);
+    trace_vhost_vdpa_set_vring_enable_one(dev, idx, enable, r);
     return r;
 }
 
+static int vhost_vdpa_set_vring_enable(struct vhost_dev *dev, int enable)
+{
+    struct vhost_vdpa *v = dev->opaque;
+    unsigned int i;
+    int ret;
+
+    for (i = 0; i < dev->nvqs; ++i) {
+        ret = vhost_vdpa_set_vring_enable_one(v, i, enable);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
+int vhost_vdpa_set_vring_ready(struct vhost_vdpa *v, unsigned idx)
+{
+    return vhost_vdpa_set_vring_enable_one(v, idx, 1);
+}
+
 static int vhost_vdpa_set_config_call(struct vhost_dev *dev,
                                        int fd)
 {
@@ -1536,6 +1558,7 @@ const VhostOps vdpa_ops = {
         .vhost_set_features = vhost_vdpa_set_features,
         .vhost_reset_device = vhost_vdpa_reset_device,
         .vhost_get_vq_index = vhost_vdpa_get_vq_index,
+        .vhost_set_vring_enable = vhost_vdpa_set_vring_enable,
         .vhost_get_config  = vhost_vdpa_get_config,
         .vhost_set_config = vhost_vdpa_set_config,
         .vhost_requires_shm_log = NULL,

hw/virtio/vhost.c

@@ -1984,7 +1984,13 @@ static int vhost_dev_set_vring_enable(struct vhost_dev *hdev, int enable)
     return hdev->vhost_ops->vhost_set_vring_enable(hdev, enable);
 }
 
-/* Host notifiers must be enabled at this point. */
+/*
+ * Host notifiers must be enabled at this point.
+ *
+ * If @vrings is true, this function will enable all vrings before starting the
+ * device. If it is false, the vring initialization is left to be done by the
+ * caller.
+ */
 int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
 {
     int i, r;