vfio-pci: Disable binding to PFs with SR-IOV enabled

awilliam · awilliam · commit 0dd0e297f0ec · 2018-08-06T12:23:19.000-06:00
We expect to receive PFs with SR-IOV disabled, however some host
drivers leave SR-IOV enabled at unbind.  This puts us in a state where
we can potentially assign both the PF and the VF, leading to both
functionality as well as security concerns due to lack of managing the
SR-IOV state as well as vendor dependent isolation from the PF to VF.
If we were to attempt to actively disable SR-IOV on driver probe, we
risk VF bound drivers blocking, potentially risking live lock
scenarios.  Therefore simply refuse to bind to PFs with SR-IOV enabled
with a warning message indicating the issue.  Users can resolve this
by re-binding to the host driver and disabling SR-IOV before
attempting to use the device with vfio-pci.

Reviewed-by: David Gibson &lt;david@gibson.dropbear.id.au&gt;
Reviewed-by: Peter Xu &lt;peterx@redhat.com&gt;
Signed-off-by: Alex Williamson &lt;alex.williamson@redhat.com&gt;
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
@@ -1193,6 +1193,19 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
 		return -EINVAL;
 
+	/*
+	 * Prevent binding to PFs with VFs enabled, this too easily allows
+	 * userspace instance with VFs and PFs from the same device, which
+	 * cannot work.  Disabling SR-IOV here would initiate removing the
+	 * VFs, which would unbind the driver, which is prone to blocking
+	 * if that VF is also in use by vfio-pci.  Just reject these PFs
+	 * and let the user sort it out.
+	 */
+	if (pci_num_vf(pdev)) {
+		pci_warn(pdev, "Cannot bind to PF with SR-IOV enabled\n");
+		return -EBUSY;
+	}
+
 	group = vfio_iommu_group_get(&pdev->dev);
 	if (!group)
 		return -EINVAL;
