virtio: allow to fail setting status

virtio-1 allow setting of the FEATURES_OK status bit to fail if
the negotiated feature bits are inconsistent: let's fail
virtio_set_status() in that case and update virtio-ccw to post an
error to the guest.
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>

hw/s390x/virtio-ccw.c

@@ -497,15 +497,19 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
             if (!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {
                 virtio_ccw_stop_ioeventfd(dev);
             }
-            virtio_set_status(vdev, status);
-            if (vdev->status == 0) {
-                virtio_reset(vdev);
-            }
-            if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
-                virtio_ccw_start_ioeventfd(dev);
+            if (virtio_set_status(vdev, status) == 0) {
+                if (vdev->status == 0) {
+                    virtio_reset(vdev);
+                }
+                if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
+                    virtio_ccw_start_ioeventfd(dev);
+                }
+                sch->curr_status.scsw.count = ccw.count - sizeof(status);
+                ret = 0;
+            } else {
+                /* Trigger a command reject. */
+                ret = -ENOSYS;
             }
-            sch->curr_status.scsw.count = ccw.count - sizeof(status);
-            ret = 0;
         }
         break;
     case CCW_CMD_SET_IND:

hw/virtio/virtio.c

@@ -544,15 +544,37 @@ void virtio_update_irq(VirtIODevice *vdev)
     virtio_notify_vector(vdev, VIRTIO_NO_VECTOR);
 }
 
-void virtio_set_status(VirtIODevice *vdev, uint8_t val)
+static int virtio_validate_features(VirtIODevice *vdev)
+{
+    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
+
+    if (k->validate_features) {
+        return k->validate_features(vdev);
+    } else {
+        return 0;
+    }
+}
+
+int virtio_set_status(VirtIODevice *vdev, uint8_t val)
 {
     VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
     trace_virtio_set_status(vdev, val);
 
+    if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+        if (!(vdev->status & VIRTIO_CONFIG_S_FEATURES_OK) &&
+            val & VIRTIO_CONFIG_S_FEATURES_OK) {
+            int ret = virtio_validate_features(vdev);
+
+            if (ret) {
+                return ret;
+            }
+        }
+    }
     if (k->set_status) {
         k->set_status(vdev, val);
     }
     vdev->status = val;
+    return 0;
 }
 
 bool target_words_bigendian(void);

include/hw/virtio/virtio.h

@@ -99,6 +99,7 @@ typedef struct VirtioDeviceClass {
     uint64_t (*get_features)(VirtIODevice *vdev, uint64_t requested_features);
     uint64_t (*bad_features)(VirtIODevice *vdev);
     void (*set_features)(VirtIODevice *vdev, uint64_t val);
+    int (*validate_features)(VirtIODevice *vdev);
     void (*get_config)(VirtIODevice *vdev, uint8_t *config);
     void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
     void (*reset)(VirtIODevice *vdev);
@@ -184,7 +185,7 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align);
 void virtio_queue_notify(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);
 void virtio_queue_set_vector(VirtIODevice *vdev, int n, uint16_t vector);
-void virtio_set_status(VirtIODevice *vdev, uint8_t val);
+int virtio_set_status(VirtIODevice *vdev, uint8_t val);
 void virtio_reset(void *opaque);
 void virtio_update_irq(VirtIODevice *vdev);
 int virtio_set_features(VirtIODevice *vdev, uint64_t val);