diff --git a/arch/ia64/kernel/irq.c b/arch/ia64/kernel/irq.c
index ce49c85c928f5fe44f52501c86211b11926c89d8..b4c239685d2eb8f0072d2510573d027ab867d1c3 100644
--- a/arch/ia64/kernel/irq.c
+++ b/arch/ia64/kernel/irq.c
@@ -104,6 +104,17 @@ void set_irq_affinity_info (unsigned int irq, int hwid, int redir)
 		irq_redir[irq] = (char) (redir & 0xff);
 	}
 }
+
+bool is_affinity_mask_valid(cpumask_t cpumask)
+{
+	if (ia64_platform_is("sn2")) {
+		/* Only allow one CPU to be specified in the smp_affinity mask */
+		if (cpus_weight(cpumask) != 1)
+			return false;
+	}
+	return true;
+}
+
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_HOTPLUG_CPU
diff --git a/include/asm-ia64/irq.h b/include/asm-ia64/irq.h
index 79479e2c6966b0cb468db6f348538e8b0e19d32f..67221615e3173537ac8df7b4ba6de436dd97db3c 100644
--- a/include/asm-ia64/irq.h
+++ b/include/asm-ia64/irq.h
@@ -11,6 +11,9 @@
  * 02/29/00     D.Mosberger	moved most things into hw_irq.h
  */
 
+#include <linux/types.h>
+#include <linux/cpumask.h>
+
 #define NR_IRQS		256
 #define NR_IRQ_VECTORS	NR_IRQS
 
@@ -29,5 +32,8 @@ extern void disable_irq (unsigned int);
 extern void disable_irq_nosync (unsigned int);
 extern void enable_irq (unsigned int);
 extern void set_irq_affinity_info (unsigned int irq, int dest, int redir);
+bool is_affinity_mask_valid(cpumask_t cpumask);
+
+#define is_affinity_mask_valid is_affinity_mask_valid
 
 #endif /* _ASM_IA64_IRQ_H */
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index ddde0ef9ccdcbb4dbd8834accc5f0264deee8403..b4f1674fca7987d8f99fa707eb2655cd20f0bc37 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -27,6 +27,10 @@ static int irq_affinity_read_proc(char *page, char **start, off_t off,
 	return len;
 }
 
+#ifndef is_affinity_mask_valid
+#define is_affinity_mask_valid(val) 1
+#endif
+
 int no_irq_affinity;
 static int irq_affinity_write_proc(struct file *file, const char __user *buffer,
 				   unsigned long count, void *data)
@@ -42,6 +46,9 @@ static int irq_affinity_write_proc(struct file *file, const char __user *buffer,
 	if (err)
 		return err;
 
+	if (!is_affinity_mask_valid(new_value))
+		return -EINVAL;
+
 	/*
 	 * Do not allow disabling IRQs completely - it's a too easy
 	 * way to make the system unusable accidentally :-) At least