Re: [PATCH v1 1/3] cpufreq: intel_pstate: Always read hwp_cap_cached with READ_ONCE()

[Chen Yu]

On Thu, Jan 07, 2021 at 07:42:15PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki 
> 
> Because intel_pstate_get_hwp_max() which updates hwp_cap_cached
> may run in parallel with the readers of it, annotate all of the
> read accesses to it with READ_ONCE().
> 
> Signed-off-by: Rafael J. Wysocki 
Tested-by: Chen Yu 

thanks,
Chenyu

[PATCH v1 1/3] cpufreq: intel_pstate: Always read hwp_cap_cached with READ_ONCE()

[Rafael J. Wysocki]

From: Rafael J. Wysocki 

Because intel_pstate_get_hwp_max() which updates hwp_cap_cached
may run in parallel with the readers of it, annotate all of the
read accesses to it with READ_ONCE().

Signed-off-by: Rafael J. Wysocki 
---
 drivers/cpufreq/intel_pstate.c |   13 +++--
 1 file changed, 7 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -914,7 +914,7 @@ static void intel_pstate_hwp_offline(str
}
 
value &= ~GENMASK_ULL(31, 0);
-   min_perf = HWP_LOWEST_PERF(cpu->hwp_cap_cached);
+   min_perf = HWP_LOWEST_PERF(READ_ONCE(cpu->hwp_cap_cached));
 
/* Set hwp_max = hwp_min */
value |= HWP_MAX_PERF(min_perf);
@@ -1750,6 +1750,7 @@ static int hwp_boost_hold_time_ns = 3 *
 static inline void intel_pstate_hwp_boost_up(struct cpudata *cpu)
 {
u64 hwp_req = READ_ONCE(cpu->hwp_req_cached);
+   u64 hwp_cap = READ_ONCE(cpu->hwp_cap_cached);
u32 max_limit = (hwp_req & 0xff00) >> 8;
u32 min_limit = (hwp_req & 0xff);
u32 boost_level1;
@@ -1776,14 +1777,14 @@ static inline void intel_pstate_hwp_boos
cpu->hwp_boost_min = min_limit;
 
/* level at half way mark between min and guranteed */
-   boost_level1 = (HWP_GUARANTEED_PERF(cpu->hwp_cap_cached) + min_limit) 
>> 1;
+   boost_level1 = (HWP_GUARANTEED_PERF(hwp_cap) + min_limit) >> 1;
 
if (cpu->hwp_boost_min < boost_level1)
cpu->hwp_boost_min = boost_level1;
-   else if (cpu->hwp_boost_min < HWP_GUARANTEED_PERF(cpu->hwp_cap_cached))
-   cpu->hwp_boost_min = HWP_GUARANTEED_PERF(cpu->hwp_cap_cached);
-   else if (cpu->hwp_boost_min == HWP_GUARANTEED_PERF(cpu->hwp_cap_cached) 
&&
-max_limit != HWP_GUARANTEED_PERF(cpu->hwp_cap_cached))
+   else if (cpu->hwp_boost_min < HWP_GUARANTEED_PERF(hwp_cap))
+   cpu->hwp_boost_min = HWP_GUARANTEED_PERF(hwp_cap);
+   else if (cpu->hwp_boost_min == HWP_GUARANTEED_PERF(hwp_cap) &&
+max_limit != HWP_GUARANTEED_PERF(hwp_cap))
cpu->hwp_boost_min = max_limit;
else
return;