linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Fix unchecked HWP MSR access

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Date: Mon, 3 Jun 2024 18:03:23 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: rafael@...nel.org, viresh.kumar@...aro.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] cpufreq: intel_pstate: Fix unchecked HWP MSR access

On Sat, Jun 1, 2024 at 1:00 AM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> Fix unchecked MSR access error for processors with no HWP support. On
> such processors, maximum frequency can be changed by the system firmware
> using ACPI event ACPI_PROCESSOR_NOTIFY_HIGEST_PERF_CHANGED. This results
> in accessing HWP MSR 0x771.
>
> Call Trace:
>         <TASK>
>         generic_exec_single+0x58/0x120
>         smp_call_function_single+0xbf/0x110
>         rdmsrl_on_cpu+0x46/0x60
>         intel_pstate_get_hwp_cap+0x1b/0x70
>         intel_pstate_update_limits+0x2a/0x60
>         acpi_processor_notify+0xb7/0x140
>         acpi_ev_notify_dispatch+0x3b/0x60
>
> HWP MSR 0x771 can be only read on a CPU which supports HWP and enabled.
> Hence intel_pstate_get_hwp_cap() can only be called when hwp_active is
> true.
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Closes: https://lore.kernel.org/linux-pm/20240529155740.Hq2Hw7be@linutronix.de/
> Fixes: e8217b4bece3 ("cpufreq: intel_pstate: Update the maximum CPU frequency consistently")
> Tested-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 4b986c044741..65d3f79104bd 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1153,7 +1153,8 @@ static void intel_pstate_update_policies(void)
>  static void __intel_pstate_update_max_freq(struct cpudata *cpudata,
>                                            struct cpufreq_policy *policy)
>  {
> -       intel_pstate_get_hwp_cap(cpudata);
> +       if (hwp_active)
> +               intel_pstate_get_hwp_cap(cpudata);
>
>         policy->cpuinfo.max_freq = READ_ONCE(global.no_turbo) ?
>                         cpudata->pstate.max_freq : cpudata->pstate.turbo_freq;
> --

Applied as 6.10-rc material, thanks!