[IA64-SGI] Silent data corruption caused by XPC V2.

Jack Steiner identified a problem where XPC can cause a silent
data corruption.  On module load, the placement may cause the
xpc_remote_copy_buffer to span two physical pages.  DMA transfers are
done to the start virtual address translated to physical.

This patch changes the buffer from a statically allocated buffer to a
kmalloc'd buffer.  Dean Nelson reviewed this before posting.  I have
tested it in the configuration that was showing the memory corruption
and verified it works.  I also added a BUG_ON statement to help catch
this if a similar situation is encountered.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

2 files changed, 21 insertions, 5 deletions

diff --git a/include/asm-ia64/sn/xp.h b/include/asm-ia64/sn/xp.h
index 9bd2f9bf329..6f807e0193b 100644
--- a/include/asm-ia64/sn/xp.h
+++ b/include/asm-ia64/sn/xp.h
@@ -60,23 +60,37 @@
  * the bte_copy() once in the hope that the failure was due to a temporary
  * aberration (i.e., the link going down temporarily).
  *
- * See bte_copy for definition of the input parameters.
+ * 	src - physical address of the source of the transfer.
+ *	vdst - virtual address of the destination of the transfer.
+ *	len - number of bytes to transfer from source to destination.
+ *	mode - see bte_copy() for definition.
+ *	notification - see bte_copy() for definition.
  *
  * Note: xp_bte_copy() should never be called while holding a spinlock.
  */
 static inline bte_result_t
-xp_bte_copy(u64 src, u64 dest, u64 len, u64 mode, void *notification)
+xp_bte_copy(u64 src, u64 vdst, u64 len, u64 mode, void *notification)
 {
 	bte_result_t ret;
+	u64 pdst = ia64_tpa(vdst);
 
 
-	ret = bte_copy(src, dest, len, mode, notification);
+	/*
+	 * Ensure that the physically mapped memory is contiguous.
+	 *
+	 * We do this by ensuring that the memory is from region 7 only.
+	 * If the need should arise to use memory from one of the other
+	 * regions, then modify the BUG_ON() statement to ensure that the
+	 * memory from that region is always physically contiguous.
+	 */
+	BUG_ON(REGION_NUMBER(vdst) != RGN_KERNEL);
 
+	ret = bte_copy(src, pdst, len, mode, notification);
 	if (ret != BTE_SUCCESS) {
 		if (!in_interrupt()) {
 			cond_resched();
 		}
-		ret = bte_copy(src, dest, len, mode, notification);
+		ret = bte_copy(src, pdst, len, mode, notification);
 	}
 
 	return ret;
diff --git a/include/asm-ia64/sn/xpc.h b/include/asm-ia64/sn/xpc.h
index b72af597878..35e1386f37a 100644
--- a/include/asm-ia64/sn/xpc.h
+++ b/include/asm-ia64/sn/xpc.h
@@ -683,7 +683,9 @@ extern struct xpc_vars *xpc_vars;
 extern struct xpc_rsvd_page *xpc_rsvd_page;
 extern struct xpc_vars_part *xpc_vars_part;
 extern struct xpc_partition xpc_partitions[XP_MAX_PARTITIONS + 1];
-extern char xpc_remote_copy_buffer[];
+extern char *xpc_remote_copy_buffer;
+extern void *xpc_remote_copy_buffer_base;
+extern void *xpc_kmalloc_cacheline_aligned(size_t, gfp_t, void **);
 extern struct xpc_rsvd_page *xpc_rsvd_page_init(void);
 extern void xpc_allow_IPI_ops(void);
 extern void xpc_restrict_IPI_ops(void);