xen-pciback: rate limit error messages from xen_pcibk_enable_msi{,x}()

... as being guest triggerable (e.g. by invoking
XEN_PCI_OP_enable_msi{,x} on a device not being MSI/MSI-X capable).

This is CVE-2013-0231 / XSA-43.

Also make the two messages uniform in both their wording and severity.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xen-pciback/pciback_ops.c

@@ -135,7 +135,6 @@ int xen_pcibk_enable_msi(struct xen_pcibk_device *pdev,
 			 struct pci_dev *dev, struct xen_pci_op *op)
 {
 	struct xen_pcibk_dev_data *dev_data;
-	int otherend = pdev->xdev->otherend_id;
 	int status;
 
 	if (unlikely(verbose_request))
@@ -144,8 +143,9 @@ int xen_pcibk_enable_msi(struct xen_pcibk_device *pdev,
 	status = pci_enable_msi(dev);
 
 	if (status) {
-		printk(KERN_ERR "error enable msi for guest %x status %x\n",
-			otherend, status);
+		pr_warn_ratelimited(DRV_NAME ": %s: error enabling MSI for guest %u: err %d\n",
+				    pci_name(dev), pdev->xdev->otherend_id,
+				    status);
 		op->value = 0;
 		return XEN_PCI_ERR_op_failed;
 	}
@@ -223,10 +223,10 @@ int xen_pcibk_enable_msix(struct xen_pcibk_device *pdev,
 						pci_name(dev), i,
 						op->msix_entries[i].vector);
 		}
-	} else {
-		printk(KERN_WARNING DRV_NAME ": %s: failed to enable MSI-X: err %d!\n",
-			pci_name(dev), result);
-	}
+	} else
+		pr_warn_ratelimited(DRV_NAME ": %s: error enabling MSI-X for guest %u: err %d!\n",
+				    pci_name(dev), pdev->xdev->otherend_id,
+				    result);
 	kfree(entries);
 
 	op->value = result;