x86: msr: propagate errors from smp_call_function_single()

Propagate error (-ENXIO) from smp_call_function_single().  These
errors can happen when a CPU is unplugged while the MSR driver is
open.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index e439380..9c34a10 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -79,8 +79,11 @@
 
 	for (; count; count -= 8) {
 		err = rdmsr_safe_on_cpu(cpu, reg, &data[0], &data[1]);
-		if (err)
-			return -EIO;
+		if (err) {
+			if (err == -EFAULT) /* Fix idiotic error code */
+				err = -EIO;
+			return err;
+		}
 		if (copy_to_user(tmp, &data, 8))
 			return -EFAULT;
 		tmp += 2;
@@ -105,8 +108,11 @@
 		if (copy_from_user(&data, tmp, 8))
 			return -EFAULT;
 		err = wrmsr_safe_on_cpu(cpu, reg, data[0], data[1]);
-		if (err)
-			return -EIO;
+		if (err) {
+			if (err == -EFAULT) /* Fix idiotic error code */
+				err = -EIO;
+			return err;
+		}
 		tmp += 2;
 	}