virtio: virtio 1.0 cs04 spec compliance for reset

The spec says: after writing 0 to device_status, the driver MUST wait
for a read of device_status to return 0 before reinitializing the
device.

Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index f6f28cc..e76bd91 100644 (file)
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -17,6 +17,7 @@
  *
  */
 
+#include <linux/delay.h>
 #define VIRTIO_PCI_NO_LEGACY
 #include "virtio_pci_common.h"
 
@@ -271,9 +272,13 @@ static void vp_reset(struct virtio_device *vdev)
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        /* 0 status means a reset. */
        vp_iowrite8(0, &vp_dev->common->device_status);
-       /* Flush out the status write, and flush in device writes,
-        * including MSI-X interrupts, if any. */
-       vp_ioread8(&vp_dev->common->device_status);
+       /* After writing 0 to device_status, the driver MUST wait for a read of
+        * device_status to return 0 before reinitializing the device.
+        * This will flush out the status write, and flush in device writes,
+        * including MSI-X interrupts, if any.
+        */
+       while (vp_ioread8(&vp_dev->common->device_status))
+               msleep(1);
        /* Flush pending VQ/configuration callbacks. */
        vp_synchronize_vectors(vdev);
 }