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>

arch/x86/kernel/msr.c

@@ -79,8 +79,11 @@ static ssize_t msr_read(struct file *file, char __user *buf,
 
 	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 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 		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;
 	}
 

arch/x86/lib/msr-on-cpu.c

@@ -30,10 +30,11 @@ static int _rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h, int safe)
 
 	rv.msr_no = msr_no;
 	if (safe) {
-		smp_call_function_single(cpu, __rdmsr_safe_on_cpu, &rv, 1);
-		err = rv.err;
+		err = smp_call_function_single(cpu, __rdmsr_safe_on_cpu,
+					       &rv, 1);
+		err = err ? err : rv.err;
 	} else {
-		smp_call_function_single(cpu, __rdmsr_on_cpu, &rv, 1);
+		err = smp_call_function_single(cpu, __rdmsr_on_cpu, &rv, 1);
 	}
 	*l = rv.l;
 	*h = rv.h;
@@ -64,23 +65,24 @@ static int _wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h, int safe)
 	rv.l = l;
 	rv.h = h;
 	if (safe) {
-		smp_call_function_single(cpu, __wrmsr_safe_on_cpu, &rv, 1);
-		err = rv.err;
+		err = smp_call_function_single(cpu, __wrmsr_safe_on_cpu,
+					       &rv, 1);
+		err = err ? err : rv.err;
 	} else {
-		smp_call_function_single(cpu, __wrmsr_on_cpu, &rv, 1);
+		err = smp_call_function_single(cpu, __wrmsr_on_cpu, &rv, 1);
 	}
 
 	return err;
 }
 
-void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+int wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
 {
-	_wrmsr_on_cpu(cpu, msr_no, l, h, 0);
+	return _wrmsr_on_cpu(cpu, msr_no, l, h, 0);
 }
 
-void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+int rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
 {
-	_rdmsr_on_cpu(cpu, msr_no, l, h, 0);
+	return _rdmsr_on_cpu(cpu, msr_no, l, h, 0);
 }
 
 /* These "safe" variants are slower and should be used when the target MSR

include/asm-x86/msr.h

@@ -192,19 +192,20 @@ do {                                                            \
 #define write_rdtscp_aux(val) wrmsr(0xc0000103, (val), 0)
 
 #ifdef CONFIG_SMP
-void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
-void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
+int rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
+int wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
 int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
-
 int wrmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
 #else  /*  CONFIG_SMP  */
-static inline void rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
+static inline int rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
 {
 	rdmsr(msr_no, *l, *h);
+	return 0;
 }
-static inline void wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
+static inline int wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h)
 {
 	wrmsr(msr_no, l, h);
+	return 0;
 }
 static inline int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no,
 				    u32 *l, u32 *h)