virtio_pci: fix virtio spec compliance on restore

On restore, virtio pci does the following:
+ set features
+ init vqs etc - device can be used at this point!
+ set ACKNOWLEDGE,DRIVER and DRIVER_OK status bits

This is in violation of the virtio spec, which
requires the following order:
- ACKNOWLEDGE
- DRIVER
- init vqs
- DRIVER_OK

This behaviour will break with hypervisors that assume spec compliant
behaviour.  It seems like a good idea to have this patch applied to
stable branches to reduce the support butden for the hypervisors.

Cc: stable@vger.kernel.org
Cc: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 30 insertions, 3 deletions

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 3d1463c6b120..add40d00dcdb 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -789,6 +789,7 @@ static int virtio_pci_restore(struct device *dev)
         struct pci_dev *pci_dev = to_pci_dev(dev);
         struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
         struct virtio_driver *drv;
+        unsigned status = 0;
         int ret;
 
         drv = container_of(vp_dev->vdev.dev.driver,
@@ -799,14 +800,40 @@ static int virtio_pci_restore(struct device *dev)
                 return ret;
 
         pci_set_master(pci_dev);
+        /* We always start by resetting the device, in case a previous
+         * driver messed it up. */
+        vp_reset(&vp_dev->vdev);
+
+        /* Acknowledge that we've seen the device. */
+        status |= VIRTIO_CONFIG_S_ACKNOWLEDGE;
+        vp_set_status(&vp_dev->vdev, status);
+
+        /* Maybe driver failed before freeze.
+         * Restore the failed status, for debugging. */
+        status |= vp_dev->saved_status & VIRTIO_CONFIG_S_FAILED;
+        vp_set_status(&vp_dev->vdev, status);
+
+        if (!drv)
+                return 0;
+
+        /* We have a driver! */
+        status |= VIRTIO_CONFIG_S_DRIVER;
+        vp_set_status(&vp_dev->vdev, status);
+
         vp_finalize_features(&vp_dev->vdev);
 
-        if (drv && drv->restore)
+        if (drv->restore) {
                 ret = drv->restore(&vp_dev->vdev);
+                if (ret) {
+                        status |= VIRTIO_CONFIG_S_FAILED;
+                        vp_set_status(&vp_dev->vdev, status);
+                        return ret;
+                }
+        }
 
         /* Finally, tell the device we're all set */
-        if (!ret)
-                vp_set_status(&vp_dev->vdev, vp_dev->saved_status);
+        status |= VIRTIO_CONFIG_S_DRIVER_OK;
+        vp_set_status(&vp_dev->vdev, status);
 
         return ret;
 }