x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo

Commit 890da9cf0983 (Revert "x86: do not use cpufreq_quick_get() for
/proc/cpuinfo "cpu MHz"") is not sufficient to restore the previous
behavior of "cpu MHz" in /proc/cpuinfo on x86 due to some changes
made after the commit it has reverted.

To address this, make the code in question use arch_freq_get_on_cpu()
which also is used by cpufreq for reporting the current frequency of
CPUs and since that function doesn't really depend on cpufreq in any
way, drop the CONFIG_CPU_FREQ dependency for the object file
containing it.

Also refactor arch_freq_get_on_cpu() somewhat to avoid IPIs and
return cached values right away if it is called very often over a
short time (to prevent user space from triggering IPI storms through
it).

Fixes: 890da9cf0983 (Revert "x86: do not use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"")
Cc: stable@kernel.org   # 4.13 - together with 890da9cf0983
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 11 insertions, 6 deletions

diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index c60922a66385..236999c54edc 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -22,7 +22,7 @@ obj-y			+= common.o
 obj-y                   += rdrand.o
 obj-y                   += match.o
 obj-y                   += bugs.o
-obj-$(CONFIG_CPU_FREQ)  += aperfmperf.o
+obj-y                   += aperfmperf.o
 
 obj-$(CONFIG_PROC_FS)   += proc.o
 obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 0ee83321a313..957813e0180d 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void *dummy)
         s64 time_delta = ktime_ms_delta(now, s->time);
         unsigned long flags;
 
-        /* Don't bother re-computing within the cache threshold time. */
-        if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
-                return;
-
         local_irq_save(flags);
         rdmsrl(MSR_IA32_APERF, aperf);
         rdmsrl(MSR_IA32_MPERF, mperf);
@@ -74,6 +70,7 @@ static void aperfmperf_snapshot_khz(void *dummy)
 
 unsigned int arch_freq_get_on_cpu(int cpu)
 {
+        s64 time_delta;
         unsigned int khz;
 
         if (!cpu_khz)
@@ -82,6 +79,12 @@ unsigned int arch_freq_get_on_cpu(int cpu)
         if (!static_cpu_has(X86_FEATURE_APERFMPERF))
                 return 0;
 
+        /* Don't bother re-computing within the cache threshold time. */
+        time_delta = ktime_ms_delta(ktime_get(), per_cpu(samples.time, cpu));
+        khz = per_cpu(samples.khz, cpu);
+        if (khz && time_delta < APERFMPERF_CACHE_THRESHOLD_MS)
+                return khz;
+
         smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1);
         khz = per_cpu(samples.khz, cpu);
         if (khz)
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 6b7e17bf0b71..4378a729b933 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -78,9 +78,11 @@ static int show_cpuinfo(struct seq_file *m, void *v)
                 seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
 
         if (cpu_has(c, X86_FEATURE_TSC)) {
-                unsigned int freq = cpufreq_quick_get(cpu);
+                unsigned int freq = arch_freq_get_on_cpu(cpu);
 
                 if (!freq)
+                        freq = cpufreq_quick_get(cpu);
+                if (!freq)
                         freq = cpu_khz;
                 seq_printf(m, "cpu MHz\t\t: %u.%03u\n",
                            freq / 1000, (freq % 1000));