Re: [PATCH] cpufreq: intel_pstate: Fix for HWP interrupt before driver is ready

[Rafael J. Wysocki]

On Sat, Sep 4, 2021 at 7:37 AM Srinivas Pandruvada
<srinivas.pandruvada@xxxxxxxxxxxxxxx> wrote:
>
> In Lenovo X1 gen9 laptop, HWP interrupts arrive before driver is ready
> to handle on that CPU. Basically didn't even allocated memory for per
> cpu data structure and not even started interrupt enable process on that
> CPU. So interrupt handler observes a NULL pointer to schedule work.
>
> This interrupt was probably for SMM, but since it is redirected to
> OS by OSC call, OS receives it, but not ready to handle. That redirection
> of interrupt to OS was also done to solve one SMM crash on Yoga 260 for
> HWP interrupt a while back.
>
> To solve this the HWP interrupt handler should ignore such request if the
> driver is not ready. This will require some flag to wait till the driver
> setup a workqueue to handle on a CPU. We can't simply assume cpudata to
> be NULL and avoid processing as it may not be NULL but data structure is
> not in consistent state.
>
> So created a cpumask which sets the CPU on which interrupt was setup. If
> not setup, simply clear the interrupt status and return. Since the
> similar issue can happen during S3 resume, clear the bit during offline.
>
> Since interrupt timing may be before HWP is enabled, use safe MSR read
> writes as before the change for HWP interrupt.
>
> Fixes: d0e936adbd22 ("cpufreq: intel_pstate: Process HWP Guaranteed change notification")
> Reported-and-tested-by: Jens Axboe <axboe@xxxxxxxxx>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> ---
>  drivers/cpufreq/intel_pstate.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index b4ffe6c8a0d0..5ac86bfa1080 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -298,6 +298,8 @@ static bool hwp_boost __read_mostly;
>
>  static struct cpufreq_driver *intel_pstate_driver __read_mostly;
>
> +static cpumask_t hwp_intr_enable_mask;
> +
>  #ifdef CONFIG_ACPI
>  static bool acpi_ppc;
>  #endif
> @@ -1067,11 +1069,15 @@ static void intel_pstate_hwp_set(unsigned int cpu)
>         wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value);
>  }
>
> +static void intel_pstate_disable_hwp_interrupt(struct cpudata *cpudata);
> +
>  static void intel_pstate_hwp_offline(struct cpudata *cpu)
>  {
>         u64 value = READ_ONCE(cpu->hwp_req_cached);
>         int min_perf;
>
> +       intel_pstate_disable_hwp_interrupt(cpu);
> +
>         if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
>                 /*
>                  * In case the EPP has been set to "performance" by the
> @@ -1645,20 +1651,35 @@ void notify_hwp_interrupt(void)
>         if (!hwp_active || !boot_cpu_has(X86_FEATURE_HWP_NOTIFY))
>                 return;
>
> -       rdmsrl(MSR_HWP_STATUS, value);
> +       rdmsrl_safe(MSR_HWP_STATUS, &value);
>         if (!(value & 0x01))
>                 return;
>
> +       if (!cpumask_test_cpu(this_cpu, &hwp_intr_enable_mask)) {
> +               wrmsrl_safe(MSR_HWP_STATUS, 0);
> +               return;
> +       }

Without additional locking, there is a race between this and
intel_pstate_disable_hwp_interrupt().

1. notify_hwp_interrupt() checks hwp_intr_enable_mask() and the target
CPU is in there, so it will go for scheduling the delayed work.
2. intel_pstate_disable_hwp_interrupt() runs between the check and the
cpudata load below.
3. hwp_notify_work is scheduled on the CPU that isn't there in the
mask any more.

I think that this should be avoided?

> +
>         cpudata = all_cpu_data[this_cpu];
>         schedule_delayed_work_on(this_cpu, &cpudata->hwp_notify_work, msecs_to_jiffies(10));
>  }
>
> +static void intel_pstate_disable_hwp_interrupt(struct cpudata *cpudata)
> +{
> +
> +       if (cpumask_test_and_clear_cpu(cpudata->cpu, &hwp_intr_enable_mask)) {
> +               wrmsrl_on_cpu(cpudata->cpu, MSR_HWP_INTERRUPT, 0x00);
> +               cancel_delayed_work_sync(&cpudata->hwp_notify_work);
> +       }
> +}
> +
>  static void intel_pstate_enable_hwp_interrupt(struct cpudata *cpudata)
>  {
>         /* Enable HWP notification interrupt for guaranteed performance change */
>         if (boot_cpu_has(X86_FEATURE_HWP_NOTIFY)) {
>                 INIT_DELAYED_WORK(&cpudata->hwp_notify_work, intel_pstate_notify_work);
>                 wrmsrl_on_cpu(cpudata->cpu, MSR_HWP_INTERRUPT, 0x01);
> +               cpumask_set_cpu(cpudata->cpu, &hwp_intr_enable_mask);
>         }
>  }
>
> --
> 2.31.1
>