1 files changed, 24 insertions, 0 deletions

diff --git a/drivers/dma/ioat_dca.c b/drivers/dma/ioat_dca.c
index 6cf622da0286..78705ca7d36a 100644
--- a/drivers/dma/ioat_dca.c
+++ b/drivers/dma/ioat_dca.c
@@ -49,6 +49,23 @@
 
 #define DCA_TAG_MAP_MASK 0xDF
 
+/* expected tag map bytes for I/OAT ver.2 */
+#define DCA2_TAG_MAP_BYTE0 0x80
+#define DCA2_TAG_MAP_BYTE1 0x0
+#define DCA2_TAG_MAP_BYTE2 0x81
+#define DCA2_TAG_MAP_BYTE3 0x82
+#define DCA2_TAG_MAP_BYTE4 0x82
+
+/* verify if tag map matches expected values */
+static inline int dca2_tag_map_valid(u8 *tag_map)
+{
+        return ((tag_map[0] == DCA2_TAG_MAP_BYTE0) &&
+                (tag_map[1] == DCA2_TAG_MAP_BYTE1) &&
+                (tag_map[2] == DCA2_TAG_MAP_BYTE2) &&
+                (tag_map[3] == DCA2_TAG_MAP_BYTE3) &&
+                (tag_map[4] == DCA2_TAG_MAP_BYTE4));
+}
+
 /*
  * "Legacy" DCA systems do not implement the DCA register set in the
  * I/OAT device.  Software needs direct support for their tag mappings.
@@ -452,6 +469,13 @@ struct dca_provider *ioat2_dca_init(struct pci_dev *pdev, void __iomem *iobase)
                         ioatdca->tag_map[i] = 0;
         }
 
+        if (!dca2_tag_map_valid(ioatdca->tag_map)) {
+                dev_err(&pdev->dev, "APICID_TAG_MAP set incorrectly by BIOS, "
+                        "disabling DCA\n");
+                free_dca_provider(dca);
+                return NULL;
+        }
+
         err = register_dca_provider(dca, &pdev->dev);
         if (err) {
                 free_dca_provider(dca);