[CPUFREQ] cpumask: avoid playing with cpus_allowed in speedstep-ich.c

Impact: don't play with current's cpumask

It's generally a very bad idea to mug some process's cpumask: it could
legitimately and reasonably be changed by root, which could break us
(if done before our code) or them (if we restore the wrong value).

We use smp_call_function_single: this had the advantage of being more
efficient, too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
To: cpufreq@vger.kernel.org
Cc: Dominik Brodowski <linux@brodo.de>
Signed-off-by: Dave Jones <davej@redhat.com>

2 files changed, 55 insertions, 39 deletions

diff --git a/arch/x86/kernel/cpu/cpufreq/speedstep-ich.c b/arch/x86/kernel/cpu/cpufreq/speedstep-ich.c
index 016c1a4fa3fc..6911e91fb4f6 100644
--- a/arch/x86/kernel/cpu/cpufreq/speedstep-ich.c
+++ b/arch/x86/kernel/cpu/cpufreq/speedstep-ich.c
@@ -89,7 +89,8 @@ static int speedstep_find_register(void)
  * speedstep_set_state - set the SpeedStep state
  * @state: new processor frequency state (SPEEDSTEP_LOW or SPEEDSTEP_HIGH)
  *
- *   Tries to change the SpeedStep state.
+ *   Tries to change the SpeedStep state.  Can be called from
+ *   smp_call_function_single.
  */
 static void speedstep_set_state(unsigned int state)
 {
@@ -143,6 +144,11 @@ static void speedstep_set_state(unsigned int state)
         return;
 }
 
+/* Wrapper for smp_call_function_single. */
+static void _speedstep_set_state(void *_state)
+{
+        speedstep_set_state(*(unsigned int *)_state);
+}
 
 /**
  * speedstep_activate - activate SpeedStep control in the chipset
@@ -226,22 +232,28 @@ static unsigned int speedstep_detect_chipset(void)
         return 0;
 }
 
-static unsigned int _speedstep_get(const struct cpumask *cpus)
-{
+struct get_freq_data {
         unsigned int speed;
-        cpumask_t cpus_allowed;
-
-        cpus_allowed = current->cpus_allowed;
-        set_cpus_allowed_ptr(current, cpus);
-        speed = speedstep_get_frequency(speedstep_processor);
-        set_cpus_allowed_ptr(current, &cpus_allowed);
-        dprintk("detected %u kHz as current frequency\n", speed);
-        return speed;
+        unsigned int processor;
+};
+
+static void get_freq_data(void *_data)
+{
+        struct get_freq_data *data = _data;
+
+        data->speed = speedstep_get_frequency(data->processor);
 }
 
 static unsigned int speedstep_get(unsigned int cpu)
 {
-        return _speedstep_get(cpumask_of(cpu));
+        struct get_freq_data data = { .processor = cpu };
+
+        /* You're supposed to ensure CPU is online. */
+        if (smp_call_function_single(cpu, get_freq_data, &data, 1) != 0)
+                BUG();
+
+        dprintk("detected %u kHz as current frequency\n", data.speed);
+        return data.speed;
 }
 
 /**
@@ -257,16 +269,16 @@ static int speedstep_target(struct cpufreq_policy *policy,
                              unsigned int target_freq,
                              unsigned int relation)
 {
-        unsigned int newstate = 0;
+        unsigned int newstate = 0, policy_cpu;
         struct cpufreq_freqs freqs;
-        cpumask_t cpus_allowed;
         int i;
 
         if (cpufreq_frequency_table_target(policy, &speedstep_freqs[0],
                                 target_freq, relation, &newstate))
                 return -EINVAL;
 
-        freqs.old = _speedstep_get(policy->cpus);
+        policy_cpu = cpumask_any_and(policy->cpus, cpu_online_mask);
+        freqs.old = speedstep_get(policy_cpu);
         freqs.new = speedstep_freqs[newstate].frequency;
         freqs.cpu = policy->cpu;
 
@@ -276,20 +288,13 @@ static int speedstep_target(struct cpufreq_policy *policy,
         if (freqs.old == freqs.new)
                 return 0;
 
-        cpus_allowed = current->cpus_allowed;
-
         for_each_cpu(i, policy->cpus) {
                 freqs.cpu = i;
                 cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
         }
 
-        /* switch to physical CPU where state is to be changed */
-        set_cpus_allowed_ptr(current, policy->cpus);
-
-        speedstep_set_state(newstate);
-
-        /* allow to be run on all CPUs */
-        set_cpus_allowed_ptr(current, &cpus_allowed);
+        smp_call_function_single(policy_cpu, _speedstep_set_state, &newstate,
+                                 true);
 
         for_each_cpu(i, policy->cpus) {
                 freqs.cpu = i;
@@ -312,33 +317,43 @@ static int speedstep_verify(struct cpufreq_policy *policy)
         return cpufreq_frequency_table_verify(policy, &speedstep_freqs[0]);
 }
 
+struct get_freqs {
+        struct cpufreq_policy *policy;
+        int ret;
+};
+
+static void get_freqs_on_cpu(void *_get_freqs)
+{
+        struct get_freqs *get_freqs = _get_freqs;
+
+        get_freqs->ret =
+                speedstep_get_freqs(speedstep_processor,
+                            &speedstep_freqs[SPEEDSTEP_LOW].frequency,
+                            &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
+                            &get_freqs->policy->cpuinfo.transition_latency,
+                            &speedstep_set_state);
+}
 
 static int speedstep_cpu_init(struct cpufreq_policy *policy)
 {
-        int result = 0;
-        unsigned int speed;
-        cpumask_t cpus_allowed;
+        int result;
+        unsigned int policy_cpu, speed;
+        struct get_freqs gf;
 
         /* only run on CPU to be set, or on its sibling */
 #ifdef CONFIG_SMP
         cpumask_copy(policy->cpus, cpu_sibling_mask(policy->cpu));
 #endif
-
-        cpus_allowed = current->cpus_allowed;
-        set_cpus_allowed_ptr(current, policy->cpus);
+        policy_cpu = cpumask_any_and(policy->cpus, cpu_online_mask);
 
         /* detect low and high frequency and transition latency */
-        result = speedstep_get_freqs(speedstep_processor,
-                                     &speedstep_freqs[SPEEDSTEP_LOW].frequency,
-                                     &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
-                                     &policy->cpuinfo.transition_latency,
-                                     &speedstep_set_state);
-        set_cpus_allowed_ptr(current, &cpus_allowed);
-        if (result)
-                return result;
+        gf.policy = policy;
+        smp_call_function_single(policy_cpu, get_freqs_on_cpu, &gf, 1);
+        if (gf.ret)
+                return gf.ret;
 
         /* get current speed setting */
-        speed = _speedstep_get(policy->cpus);
+        speed = speedstep_get(policy_cpu);
         if (!speed)
                 return -EIO;
 
diff --git a/arch/x86/kernel/cpu/cpufreq/speedstep-lib.c b/arch/x86/kernel/cpu/cpufreq/speedstep-lib.c
index 2e3c6862657b..f4c290b8482f 100644
--- a/arch/x86/kernel/cpu/cpufreq/speedstep-lib.c
+++ b/arch/x86/kernel/cpu/cpufreq/speedstep-lib.c
@@ -226,6 +226,7 @@ static unsigned int pentium4_get_frequency(void)
 }
 
 
+/* Warning: may get called from smp_call_function_single. */
 unsigned int speedstep_get_frequency(unsigned int processor)
 {
         switch (processor) {