1 files changed, 22 insertions, 1 deletions

diff --git a/arch/ia64/sn/kernel/sn2/sn2_smp.c b/arch/ia64/sn/kernel/sn2/sn2_smp.c
index 471bbaa65d1b..1b33fd5e4e3a 100644
--- a/arch/ia64/sn/kernel/sn2/sn2_smp.c
+++ b/arch/ia64/sn/kernel/sn2/sn2_smp.c
@@ -5,7 +5,7 @@
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
- * Copyright (C) 2000-2005 Silicon Graphics, Inc. All rights reserved.
+ * Copyright (C) 2000-2006 Silicon Graphics, Inc. All rights reserved.
  */
 
 #include <linux/init.h>
@@ -169,6 +169,27 @@ static inline unsigned long wait_piowc(void)
         return ws;
 }
 
+/**
+ * sn_migrate - SN-specific task migration actions
+ * @task: Task being migrated to new CPU
+ *
+ * SN2 PIO writes from separate CPUs are not guaranteed to arrive in order.
+ * Context switching user threads which have memory-mapped MMIO may cause
+ * PIOs to issue from seperate CPUs, thus the PIO writes must be drained
+ * from the previous CPU's Shub before execution resumes on the new CPU.
+ */
+void sn_migrate(struct task_struct *task)
+{
+        pda_t *last_pda = pdacpu(task_thread_info(task)->last_cpu);
+        volatile unsigned long *adr = last_pda->pio_write_status_addr;
+        unsigned long val = last_pda->pio_write_status_val;
+
+        /* Drain PIO writes from old CPU's Shub */
+        while (unlikely((*adr & SH_PIO_WRITE_STATUS_PENDING_WRITE_COUNT_MASK)
+                        != val))
+                cpu_relax();
+}
+
 void sn_tlb_migrate_finish(struct mm_struct *mm)
 {
         if (mm == current->mm)