linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Avoid using CPPC when ACPI CPC is not valid

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Message-ID: <CAJZ5v0gaCgqJy59YEp3KPOGO9W99rLFUDJ1Bw5iGLokA-U5R_Q@mail.gmail.com>
Date:   Thu, 18 Nov 2021 14:14:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "open list:INTEL PSTATE DRIVER" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Avoid using CPPC when ACPI CPC is
 not valid

On Thu, Nov 18, 2021 at 1:46 PM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> If ACPI CPC is not valid, dereference cpc_desc in cppc_get_perf() causes
> a NULL pointer dereference. So avoid using CPPC for that scenario.
>
> Fixes: 46573fd6369f ("cpufreq: intel_pstate: hybrid: Rework HWP calibration")
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>

The bug is real, but it is not in intel_pstate.

cppc_get_perf() should return an error in that case.

Let me fix this.

> ---
>  drivers/cpufreq/intel_pstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 815df3daae9df..24c7d705b99b6 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -3369,7 +3369,7 @@ static int __init intel_pstate_init(void)
>                         if (!default_driver)
>                                 default_driver = &intel_pstate;
>
> -                       if (boot_cpu_has(X86_FEATURE_HYBRID_CPU))
> +                       if (boot_cpu_has(X86_FEATURE_HYBRID_CPU) && acpi_cpc_valid())
>                                 intel_pstate_cppc_set_cpu_scaling();
>
>                         goto hwp_cpu_matched;
> --
> 2.32.0
>