linux-kernel - Re: [PATCH][rfc] intel_pstate: Fix user input of min/max to legal policy region

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Date:	Mon, 07 Sep 2015 23:47:29 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Chen Yu <yu.c.chen@...el.com>, kristen@...ux.intel.com
Cc:	viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, rui.zhang@...el.com, lenb@...nel.org
Subject: Re: [PATCH][rfc] intel_pstate: Fix user input of min/max to legal policy region

On Wednesday, August 12, 2015 11:49:19 AM Chen Yu wrote:
> In current code, if system is using performance policy, user can
> modify the max_perf_pct to any values lower than 100:
> 
> $ grep . /sys/devices/system/cpu/intel_pstate/m*_perf_pct
> /sys/devices/system/cpu/intel_pstate/max_perf_pct:100
> /sys/devices/system/cpu/intel_pstate/min_perf_pct:100
> 
> $ echo 80 > /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 
> $ grep . /sys/devices/system/cpu/intel_pstate/m*_perf_pct
> /sys/devices/system/cpu/intel_pstate/max_perf_pct:80
> /sys/devices/system/cpu/intel_pstate/min_perf_pct:100
> 
> the max_perf_pct above is lower than min_perf_pct, which
> is not reasonable.
> 
> This patch solves this problem by clamping min_perf_pct and max_perf_pct
> to be strictly inside [min_policy_pct,max_policy_pct].
> 
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>

Looks reasonable to me.

Kristen, any objections?


> ---
>  drivers/cpufreq/intel_pstate.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index fcb929e..3702c5a 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -423,6 +423,7 @@ static ssize_t store_max_perf_pct(struct kobject *a, struct attribute *b,
>  
>  	limits.max_sysfs_pct = clamp_t(int, input, 0 , 100);
>  	limits.max_perf_pct = min(limits.max_policy_pct, limits.max_sysfs_pct);
> +	limits.max_perf_pct = max(limits.min_policy_pct, limits.max_perf_pct);
>  	limits.max_perf = div_fp(int_tofp(limits.max_perf_pct), int_tofp(100));
>  
>  	if (hwp_active)
> @@ -442,6 +443,7 @@ static ssize_t store_min_perf_pct(struct kobject *a, struct attribute *b,
>  
>  	limits.min_sysfs_pct = clamp_t(int, input, 0 , 100);
>  	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
> +	limits.min_perf_pct = min(limits.max_policy_pct, limits.min_perf_pct);
>  	limits.min_perf = div_fp(int_tofp(limits.min_perf_pct), int_tofp(100));
>  
>  	if (hwp_active)
> @@ -985,12 +987,14 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>  
>  	limits.min_policy_pct = (policy->min * 100) / policy->cpuinfo.max_freq;
>  	limits.min_policy_pct = clamp_t(int, limits.min_policy_pct, 0 , 100);
> -	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
> -	limits.min_perf = div_fp(int_tofp(limits.min_perf_pct), int_tofp(100));
> -
>  	limits.max_policy_pct = (policy->max * 100) / policy->cpuinfo.max_freq;
>  	limits.max_policy_pct = clamp_t(int, limits.max_policy_pct, 0 , 100);
> +
> +	limits.min_perf_pct = max(limits.min_policy_pct, limits.min_sysfs_pct);
> +	limits.min_perf_pct = min(limits.max_policy_pct, limits.min_perf_pct);
> +	limits.min_perf = div_fp(int_tofp(limits.min_perf_pct), int_tofp(100));
>  	limits.max_perf_pct = min(limits.max_policy_pct, limits.max_sysfs_pct);
> +	limits.max_perf_pct = max(limits.min_policy_pct, limits.max_perf_pct);
>  	limits.max_perf = div_fp(int_tofp(limits.max_perf_pct), int_tofp(100));
>  
>  	if (hwp_active)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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