diff --git a/drivers/infiniband/hw/ipath/ipath_kernel.h b/drivers/infiniband/hw/ipath/ipath_kernel.h
index 2a0e9a430634c99155d5021b0162650904526b8a..02134cb3e944489c1c70f39743b7209bbf1c4fe0 100644
--- a/drivers/infiniband/hw/ipath/ipath_kernel.h
+++ b/drivers/infiniband/hw/ipath/ipath_kernel.h
@@ -336,6 +336,8 @@ struct ipath_devdata {
 	u8 ipath_ht_slave_off;
 	/* for write combining settings */
 	unsigned long ipath_wc_cookie;
+	unsigned long ipath_wc_base;
+	unsigned long ipath_wc_len;
 	/* ref count for each pkey */
 	atomic_t ipath_pkeyrefs[4];
 	/* shadow copy of all exptids physaddr; used only by funcsim */
diff --git a/drivers/infiniband/hw/ipath/ipath_wc_x86_64.c b/drivers/infiniband/hw/ipath/ipath_wc_x86_64.c
index f8f9e2e8cbdd6217642076ff7842ed0b9036427b..04696e62da878ac3322d483bec9d62afbd3c7164 100644
--- a/drivers/infiniband/hw/ipath/ipath_wc_x86_64.c
+++ b/drivers/infiniband/hw/ipath/ipath_wc_x86_64.c
@@ -123,6 +123,8 @@ int ipath_enable_wc(struct ipath_devdata *dd)
 			ipath_cdbg(VERBOSE, "Set mtrr for chip to WC, "
 				   "cookie is %d\n", cookie);
 			dd->ipath_wc_cookie = cookie;
+			dd->ipath_wc_base = (unsigned long) pioaddr;
+			dd->ipath_wc_len = (unsigned long) piolen;
 		}
 	}
 
@@ -136,9 +138,16 @@ int ipath_enable_wc(struct ipath_devdata *dd)
 void ipath_disable_wc(struct ipath_devdata *dd)
 {
 	if (dd->ipath_wc_cookie) {
+		int r;
 		ipath_cdbg(VERBOSE, "undoing WCCOMB on pio buffers\n");
-		mtrr_del(dd->ipath_wc_cookie, 0, 0);
-		dd->ipath_wc_cookie = 0;
+		r = mtrr_del(dd->ipath_wc_cookie, dd->ipath_wc_base,
+			     dd->ipath_wc_len);
+		if (r < 0)
+			dev_info(&dd->pcidev->dev,
+				 "mtrr_del(%lx, %lx, %lx) failed: %d\n",
+				 dd->ipath_wc_cookie, dd->ipath_wc_base,
+				 dd->ipath_wc_len, r);
+		dd->ipath_wc_cookie = 0; /* even on failure */
 	}
 }