vfio/pci: Add test for BAR restore

If a device is reset without the memory or i/o bits enabled in the
command register we may not detect it, potentially leaving the device
without valid BAR programming.  Add an additional test to check the
BARs on each write to the command register.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_config.c

@@ -522,6 +522,23 @@ static int vfio_basic_config_read(struct vfio_pci_device *vdev, int pos,
 	return count;
 }
 
+/* Test whether BARs match the value we think they should contain */
+static bool vfio_need_bar_restore(struct vfio_pci_device *vdev)
+{
+	int i = 0, pos = PCI_BASE_ADDRESS_0, ret;
+	u32 bar;
+
+	for (; pos <= PCI_BASE_ADDRESS_5; i++, pos += 4) {
+		if (vdev->rbar[i]) {
+			ret = pci_user_read_config_dword(vdev->pdev, pos, &bar);
+			if (ret || vdev->rbar[i] != bar)
+				return true;
+		}
+	}
+
+	return false;
+}
+
 static int vfio_basic_config_write(struct vfio_pci_device *vdev, int pos,
 				   int count, struct perm_bits *perm,
 				   int offset, __le32 val)
@@ -560,7 +577,8 @@ static int vfio_basic_config_write(struct vfio_pci_device *vdev, int pos,
 		 * SR-IOV devices will trigger this, but we catch them later
 		 */
 		if ((new_mem && virt_mem && !phys_mem) ||
-		    (new_io && virt_io && !phys_io))
+		    (new_io && virt_io && !phys_io) ||
+		    vfio_need_bar_restore(vdev))
 			vfio_bar_restore(vdev);
 	}