linux-kernel - Re: [PATCH v2 02/17] cpufreq/amd-pstate: Drop min and max cached frequencies

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z7LZg8oq3LqfKZID@BLRRASHENOY1.amd.com>
Date: Mon, 17 Feb 2025 12:08:59 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Mario Limonciello <superm1@...nel.org>
Cc: Perry Yuan <perry.yuan@....com>,
	Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>,
	"open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>,
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v2 02/17] cpufreq/amd-pstate: Drop min and max cached
 frequencies

Hello Mario,

On Fri, Feb 14, 2025 at 06:52:29PM -0600, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> Use the perf_to_freq helpers to calculate this on the fly.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> --
> v2:
>  * Keep cached limits
> ---

[..snip..]

> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -717,7 +717,7 @@ static int amd_pstate_cpu_boost_update(struct cpufreq_policy *policy, bool on)
>  	int ret = 0;
>  
>  	nominal_freq = READ_ONCE(cpudata->nominal_freq);
> -	max_freq = READ_ONCE(cpudata->max_freq);
> +	max_freq = perf_to_freq(cpudata, READ_ONCE(cpudata->highest_perf));
>  
>  	if (on)
>  		policy->cpuinfo.max_freq = max_freq;
> @@ -901,35 +901,25 @@ static u32 amd_pstate_get_transition_latency(unsigned int cpu)
>  static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
>  {
>  	int ret;
> -	u32 min_freq, max_freq;
> -	u32 nominal_freq, lowest_nonlinear_freq;
> +	u32 min_freq, nominal_freq, lowest_nonlinear_freq;
>  	struct cppc_perf_caps cppc_perf;
>  
>  	ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
>  	if (ret)
>  		return ret;
>  
> -	if (quirks && quirks->lowest_freq)
> -		min_freq = quirks->lowest_freq;
> -	else
> -		min_freq = cppc_perf.lowest_freq;
> -
>  	if (quirks && quirks->nominal_freq)
>  		nominal_freq = quirks->nominal_freq;
>  	else
>  		nominal_freq = cppc_perf.nominal_freq;
>  
> -	min_freq *= 1000;
>  	nominal_freq *= 1000;
> -
>  	WRITE_ONCE(cpudata->nominal_freq, nominal_freq);

So cpudata->nominal_freq will be in KHz here.


> -	WRITE_ONCE(cpudata->min_freq, min_freq);
> -
> -	max_freq = perf_to_freq(cpudata, cpudata->highest_perf);
> -	lowest_nonlinear_freq = perf_to_freq(cpudata, cpudata->lowest_nonlinear_perf);
>  
> -	WRITE_ONCE(cpudata->lowest_nonlinear_freq, lowest_nonlinear_freq);
> -	WRITE_ONCE(cpudata->max_freq, max_freq);
> +	if (quirks && quirks->lowest_freq) {
> +		min_freq = quirks->lowest_freq;
> +	} else
> +		min_freq = cppc_perf.lowest_freq;
>

Since cppc_perf exposes the frequency values in MHz, min_freq is in MHz.

>  	/**
>  	 * Below values need to be initialized correctly, otherwise driver will fail to load
> @@ -937,12 +927,15 @@ static int amd_pstate_init_freq(struct amd_cpudata *cpudata)
>  	 * lowest_nonlinear_freq is a value between [min_freq, nominal_freq]
>  	 * Check _CPC in ACPI table objects if any values are incorrect
>  	 */
> -	if (min_freq <= 0 || max_freq <= 0 || nominal_freq <= 0 || min_freq > max_freq) {
> -		pr_err("min_freq(%d) or max_freq(%d) or nominal_freq(%d) value is incorrect\n",
> -			min_freq, max_freq, nominal_freq);
> +	if (nominal_freq <= 0) {
> +		pr_err("nominal_freq(%d) value is incorrect\n",
> +			nominal_freq);
>  		return -EINVAL;
>  	}
>  
> +	lowest_nonlinear_freq = perf_to_freq(cpudata, cpudata->lowest_nonlinear_perf);

Since lowest_nonlinear_freq will be computed using cpudata->nominal_freq, the former will be in KHz.

> +	WRITE_ONCE(cpudata->lowest_nonlinear_freq, lowest_nonlinear_freq);
> +
>  	if (lowest_nonlinear_freq <= min_freq || lowest_nonlinear_freq > nominal_freq) {
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

And thus since lowest_nonlinear_freq is in KHz and min_freq is in MHz, this check will always be true.

Shouldn't the min_freq be multiplied by 1000 ? 
   

>  		pr_err("lowest_nonlinear_freq(%d) value is out of range [min_freq(%d), nominal_freq(%d)]\n",
>  			lowest_nonlinear_freq, min_freq, nominal_freq);


-- 
Thanks and Regards
gautham.