Re: [PATCH v5 07/10] platform/x86/intel/ifs: Add scan test support

[Peter Zijlstra <peterz@infradead.org>]

On Thu, May 05, 2022 at 11:32:04AM -0700, Luck, Tony wrote:

> Patch now looks like this. Author credit to Peter ... are you willing
> to add a Signed-off-by to stop checkpatch from whining at me?

sure, see below.

> There isn't a "Something-similar-suggested-by:" tag to credit Thomas
> with this.  Perhaps "Inspired-by:"?

I'm all for creative one off tags, there's some marvelous ones in the
tree, but we always need more :-)

> -Tony
> 
> 
> From df5ca8024997d3d782978d154cfbff5147f451ad Mon Sep 17 00:00:00 2001
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Thu, 5 May 2022 08:55:09 -0700
> Subject: [PATCH] stop_machine: Add stop_core_cpuslocked() for per-core
>  operations
> 
> Hardware core level testing features require near simultaneous execution
> of WRMSR instructions on all threads of a core to initiate a test.
> 
> Provide a customized cut down version of stop_machine_cpuslocked() that
> just operates on the threads of a single core.
> 
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>  include/linux/stop_machine.h | 16 ++++++++++++++++
>  kernel/stop_machine.c        | 19 +++++++++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
> index 46fb3ebdd16e..ea7a74ea7389 100644
> --- a/include/linux/stop_machine.h
> +++ b/include/linux/stop_machine.h
> @@ -124,6 +124,22 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
>   */
>  int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
>  
> +/**
> + * stop_core_cpuslocked: - stop all threads on just one core
> + * @cpu: any cpu in the targeted core
> + * @fn: the function to run
> + * @data: the data ptr for @fn()
> + *
> + * Same as above, but instead of every CPU, only the logical CPUs of a
> + * single core are affected.
> + *
> + * Context: Must be called from within a cpus_read_lock() protected region.
> + *
> + * Return: 0 if all executions of @fn returned 0, any non zero return
> + * value if any returned non zero.
> + */
> +int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data);
> +
>  int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
>  				   const struct cpumask *cpus);
>  #else	/* CONFIG_SMP || CONFIG_HOTPLUG_CPU */
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index cbc30271ea4d..579761729836 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -633,6 +633,25 @@ int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
>  }
>  EXPORT_SYMBOL_GPL(stop_machine);
>  
> +int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
> +{
> +	const struct cpumask *smt_mask = cpu_smt_mask(cpu);
> +
> +	struct multi_stop_data msdata = {
> +		.fn = fn,
> +		.data = data,
> +		.num_threads = cpumask_weight(smt_mask),
> +		.active_cpus = smt_mask,
> +	};
> +
> +	lockdep_assert_cpus_held();
> +
> +	/* Set the initial state and stop all online cpus. */
> +	set_state(&msdata, MULTI_STOP_PREPARE);
> +	return stop_cpus(smt_mask, multi_cpu_stop, &msdata);
> +}
> +EXPORT_SYMBOL_GPL(stop_core_cpuslocked);
> +
>  /**
>   * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
>   * @fn: the function to run
> -- 
> 2.35.1
>