| Message ID | 1830825.NTYOMyctnU@aspire.rjw.lan (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On 11/13/17 at 02:15P, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > Even though aperfmperf_snapshot_khz() caches the samples.khz value > to return if called again in a sufficiently short time, its caller, > arch_freq_get_on_cpu(), still uses smp_call_function_single() to run > it which may allow user space to trigger an IPI storm by reading from > the scaling_cur_freq cpufreq sysfs file in a tight loop. > > To avoid that, move the decision on whether or not to return the > cached samples.khz value to arch_freq_get_on_cpu(). > > Fixes: 4815d3c56d1e (cpufreq: x86: Make scaling_cur_freq behave more as expected) > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Looks good to me. Reviewed-by: WANG Chao <chao.wang@ucloud.cn> > --- > > This change was part of commit 941f5f0f6ef5 (x86: CPU: Fix up "cpu MHz" in > /proc/cpuinfo), but it was not the reason for the revert and it remains > applicable. > > Thanks, > Rafael > > --- > arch/x86/kernel/cpu/Makefile | 2 +- > arch/x86/kernel/cpu/aperfmperf.c | 11 +++++++---- > arch/x86/kernel/cpu/proc.c | 4 +++- > 3 files changed, 11 insertions(+), 6 deletions(-) > > Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c > =================================================================== > --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c > +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c > @@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void > 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 > > 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 cp > 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) >
Index: linux-pm/arch/x86/kernel/cpu/aperfmperf.c =================================================================== --- linux-pm.orig/arch/x86/kernel/cpu/aperfmperf.c +++ linux-pm/arch/x86/kernel/cpu/aperfmperf.c @@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void 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 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 cp 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)