[PATCH] cpufreq: x86: Disable interrupts during MSRs reading

[Doug Smythies]

According to Intel 64 and IA-32 Architectures SDM, Volume 3,
Chapter 14.2, "Software needs to exercise care to avoid delays
between the two RDMSRs (for example interrupts)".

So, disable interrupts during reading MSRs IA32_APERF and IA32_MPERF.

See also:
commit 4ab60c3f32c721e46217e762bcd3e55a8f659c04
cpufreq: intel_pstate: Disable interrupts during MSRs reading

Signed-off-by: Doug Smythies <dsmyth...@telus.net>
---
 arch/x86/kernel/cpu/aperfmperf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 7cf7c70..0ee8332 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -40,13 +40,16 @@ static void aperfmperf_snapshot_khz(void *dummy)
        struct aperfmperf_sample *s = this_cpu_ptr(&samples);
        ktime_t now = ktime_get();
        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);
+       local_irq_restore(flags);
 
        aperf_delta = aperf - s->aperf;
        mperf_delta = mperf - s->mperf;
-- 
2.7.4