virtio-pci: make reset operation safer

virtio pci device reset actually just does an I/O
write, which in PCI is really posted, that is it
can complete on CPU before the device has received it.

Further, interrupts might have been pending on
another CPU, so device callback might get invoked after reset.

This conflicts with how drivers use reset, which is typically:
	reset
	unregister
a callback running after reset completed can race with
unregister, potentially leading to use after free bugs.

Fix by flushing out the write, and flushing pending interrupts.

This assumes that device is never reset from
its vq/config callbacks, or in parallel with being
added/removed, document this assumption.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 3d1bf41e8892b8e2150a51403726ebb52ea9d56c..03d1984bd3635042b6bbe19f9966dfe89068e1ff 100644 (file)
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -169,11 +169,29 @@ static void vp_set_status(struct virtio_device *vdev, u8 status)
        iowrite8(status, vp_dev->ioaddr + VIRTIO_PCI_STATUS);
 }
 
+/* wait for pending irq handlers */
+static void vp_synchronize_vectors(struct virtio_device *vdev)
+{
+       struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+       int i;
+
+       if (vp_dev->intx_enabled)
+               synchronize_irq(vp_dev->pci_dev->irq);
+
+       for (i = 0; i < vp_dev->msix_vectors; ++i)
+               synchronize_irq(vp_dev->msix_entries[i].vector);
+}
+
 static void vp_reset(struct virtio_device *vdev)
 {
        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
        /* 0 status means a reset. */
        iowrite8(0, vp_dev->ioaddr + VIRTIO_PCI_STATUS);
+       /* Flush out the status write, and flush in device writes,
+        * including MSi-X interrupts, if any. */
+       ioread8(vp_dev->ioaddr + VIRTIO_PCI_STATUS);
+       /* Flush pending VQ/configuration callbacks. */
+       vp_synchronize_vectors(vdev);
 }
 
 /* the notify function used when creating a virt queue */

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index add4790b21fe4ee18635db9456a43db71bb39997..e9e72bda1b72b89b8f4354b507f7b392291ec0ec 100644 (file)
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -85,6 +85,8 @@
  * @reset: reset the device
  *     vdev: the virtio device
  *     After this, status and feature negotiation must be done again
+ *     Device must not be reset from its vq/config callbacks, or in
+ *     parallel with being added/removed.
  * @find_vqs: find virtqueues and instantiate them.
  *     vdev: the virtio_device
  *     nvqs: the number of virtqueues to find