[PATCH RFC] virtio_pci: fix virtio spec compliance on restore

Discussion:

Michael S. Tsirkin

2014-09-23 10:32:22 UTC

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

Cc: stable at vger.kernel.org
Cc: Amit Shah <amit.shah at redhat.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---

Lightly tested.
Will repost as non-RFC once testing is done, sending
out now for early flames/comments.

Thanks!

drivers/virtio/virtio_pci.c | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 58f7e45..58cbf6e 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -785,6 +785,7 @@ 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,
@@ -795,14 +796,41 @@ 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)
- ret = drv->restore(&vp_dev->vdev);
+ if (!drv->restore)
+ return 0;
+
+ 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;
}

--
MST

Eric Northup

2014-09-23 16:06:03 UTC

Permalink

Post by Michael S. Tsirkin
+ 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
- ACKNOWLEDGE
- DRIVER
- init vqs
- DRIVER_OK
Cc: stable at vger.kernel.org
Cc: Amit Shah <amit.shah at redhat.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
Lightly tested.
Will repost as non-RFC once testing is done, sending
out now for early flames/comments.
Thanks!
drivers/virtio/virtio_pci.c | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 58f7e45..58cbf6e 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -785,6 +785,7 @@ 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,
@@ -795,14 +796,41 @@ 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);

This should happen before enabling PCI bus mastering.

Post by Michael S. Tsirkin
+
+ /* 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)
- ret = drv->restore(&vp_dev->vdev);
+ if (!drv->restore)
+ return 0;
+
+ 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;
}
--
MST
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Michael S. Tsirkin

2014-09-23 18:02:18 UTC

Permalink

Post by Eric Northup

This should happen before enabling PCI bus mastering.

this is the order of events in initialization,
it seems better to be consistent.

Post by Eric Northup

Ben Hutchings

2014-09-24 01:27:27 UTC

Permalink

[...]

What concrete problem does this fix, such that it should be applied to
stable branches?

Ben.
--
Ben Hutchings
Everything should be made as simple as possible, but not simpler.
- Albert Einstein
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Michael S. Tsirkin

2014-09-24 11:59:13 UTC

Permalink

Post by Ben Hutchings

[...]
What concrete problem does this fix, such that it should be applied to
stable branches?
Ben.

It will break with hypervisors that assume spec compliant behaviour.
I would like this applied to stable branches so hypervisors don't
need to support broken behaviour forever.

--
MST

Amit Shah

2014-09-24 12:27:00 UTC

Permalink

What tests are you running?

Post by Michael S. Tsirkin
Thanks!
drivers/virtio/virtio_pci.c | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 58f7e45..58cbf6e 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -785,6 +785,7 @@ 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,
@@ -795,14 +796,41 @@ 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)
- ret = drv->restore(&vp_dev->vdev);
+ if (!drv->restore)
+ return 0;

So in this case DRIVER_OK will never be set?

Post by Michael S. Tsirkin
+
+ 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;
}

Amit