[PATCH] virtio-pci: fix queue_enable write

[Jason Wang]

Spec said: The driver uses this to selectively prevent the device from
executing requests from this virtqueue. 1 - enabled; 0 - disabled.

Though write 0 to queue_enable is forbidden by the sepc, we should not
assume that the value is 1.

Fix this by ignoring the write value other than 1.

Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Stefan Hajnoczi <stefa...@redhat.com>
Signed-off-by: Jason Wang <jasow...@redhat.com>
---
 hw/virtio/virtio-pci.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index d028c17c24..b3558eeaee 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1273,16 +1273,18 @@ static void virtio_pci_common_write(void *opaque, 
hwaddr addr,
         virtio_queue_set_vector(vdev, vdev->queue_sel, val);
         break;
     case VIRTIO_PCI_COMMON_Q_ENABLE:
-        virtio_queue_set_num(vdev, vdev->queue_sel,
-                             proxy->vqs[vdev->queue_sel].num);
-        virtio_queue_set_rings(vdev, vdev->queue_sel,
+        if (val == 1) {
+            virtio_queue_set_num(vdev, vdev->queue_sel,
+                                 proxy->vqs[vdev->queue_sel].num);
+            virtio_queue_set_rings(vdev, vdev->queue_sel,
                        ((uint64_t)proxy->vqs[vdev->queue_sel].desc[1]) << 32 |
                        proxy->vqs[vdev->queue_sel].desc[0],
                        ((uint64_t)proxy->vqs[vdev->queue_sel].avail[1]) << 32 |
                        proxy->vqs[vdev->queue_sel].avail[0],
                        ((uint64_t)proxy->vqs[vdev->queue_sel].used[1]) << 32 |
                        proxy->vqs[vdev->queue_sel].used[0]);
-        proxy->vqs[vdev->queue_sel].enabled = 1;
+            proxy->vqs[vdev->queue_sel].enabled = 1;
+        }
         break;
     case VIRTIO_PCI_COMMON_Q_DESCLO:
         proxy->vqs[vdev->queue_sel].desc[0] = val;
-- 
2.20.1