Date:   Sun, 24 Sep 2023 08:29:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Nikolay Borisov <nik.borisov@...e.com>
Subject: Re: [patch V3 21/30] x86/microcode: Add per CPU result state

On Tue, Sep 12, 2023 at 09:58:16AM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The microcode rendevouz is purely acting on global state, which does not

rendezvous

> allow to analyze fails in a coherent way.
> 
> Introduce per CPU state where the results are written into, which allows to
> analyze the return codes of the individual CPUs.
> 
> Initialize the state when walking the cpu_present_mask in the online check
> to avoid another for_each_cpu() loop.
> 
> Enhance the result print out with that.
> 
> The structure is intentionally named ucode_ctrl as it will gain control
> fields in subsequent changes.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>  arch/x86/kernel/cpu/microcode/core.c     |  108 ++++++++++++++++++-------------
>  arch/x86/kernel/cpu/microcode/internal.h |    1 
>  2 files changed, 65 insertions(+), 44 deletions(-)
> ---
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -324,6 +324,11 @@ static struct platform_device	*microcode
>   *   requirement can be relaxed in the future. Right now, this is conservative
>   *   and good.
>   */
> +struct ucode_ctrl {

microcode_ctrl

I know "ucode" is shorter but we already call everything new-er
"microcode_" and this'll cause confusion.

> +	enum ucode_state	result;
> +};
> +
> +static DEFINE_PER_CPU(struct ucode_ctrl, ucode_ctrl);

You could do

static DEFINE_PER_CPU(struct microcode_ctrl, ucode_ctrl);

so that the naming is different too.

>  static atomic_t late_cpus_in, late_cpus_out;
>  
>  static bool wait_for_cpus(atomic_t *cnt)
> @@ -344,23 +349,19 @@ static bool wait_for_cpus(atomic_t *cnt)
>  	return false;
>  }
>  
> -/*
> - * Returns:
> - * < 0 - on error
> - *   0 - success (no update done or microcode was updated)
> - */
> -static int __reload_late(void *info)
> +static int ucode_load_cpus_stopped(void *unused)

No need for "ucode_" prefixes to static functions.

>  {
>  	int cpu = smp_processor_id();
> -	enum ucode_state err;
> -	int ret = 0;
> +	enum ucode_state ret;
>  
>  	/*
>  	 * Wait for all CPUs to arrive. A load will not be attempted unless all
>  	 * CPUs show up.
>  	 * */
> -	if (!wait_for_cpus(&late_cpus_in))
> -		return -1;
> +	if (!wait_for_cpus(&late_cpus_in)) {
> +		this_cpu_write(ucode_ctrl.result, UCODE_TIMEOUT);
> +		return 0;

So the only value this function returns is 0 now.
stop_machine_cpuslocked() still does pay attention at ret so I guess it
should return non-null/negative on error or so?

>  	/*
>  	 * On an SMT system, it suffices to load the microcode on one sibling of
> @@ -369,17 +370,11 @@ static int __reload_late(void *info)
>  	 * loading attempts happen on multiple threads of an SMT core. See
>  	 * below.
>  	 */
> -	if (cpumask_first(topology_sibling_cpumask(cpu)) == cpu)
> -		err = microcode_ops->apply_microcode(cpu);
> -	else
> +	if (cpumask_first(topology_sibling_cpumask(cpu)) != cpu)
>  		goto wait_for_siblings;
>  
> -	if (err >= UCODE_NFOUND) {
> -		if (err == UCODE_ERROR) {
> -			pr_warn("Error reloading microcode on CPU %d\n", cpu);
> -			ret = -1;
> -		}
> -	}
> +	ret = microcode_ops->apply_microcode(cpu);
> +	this_cpu_write(ucode_ctrl.result, ret);
>  
>  wait_for_siblings:
>  	if (!wait_for_cpus(&late_cpus_out))
> @@ -391,19 +386,18 @@ static int __reload_late(void *info)
>  	 * per-cpu cpuinfo can be updated with right microcode
>  	 * revision.
>  	 */
> -	if (cpumask_first(topology_sibling_cpumask(cpu)) != cpu)
> -		err = microcode_ops->apply_microcode(cpu);
> +	if (cpumask_first(topology_sibling_cpumask(cpu)) == cpu)
> +		return 0;
>  
> -	return ret;
> +	ret = microcode_ops->apply_microcode(cpu);
> +	this_cpu_write(ucode_ctrl.result, ret);
> +	return 0;
>  }
>  
> -/*
> - * Reload microcode late on all CPUs. Wait for a sec until they
> - * all gather together.
> - */
> -static int microcode_reload_late(void)
> +static int ucode_load_late_stop_cpus(void)

s/ucode_//

>  {
> -	int old = boot_cpu_data.microcode, ret;
> +	unsigned int cpu, updated = 0, failed = 0, timedout = 0, siblings = 0;
> +	int old_rev = boot_cpu_data.microcode;
>  	struct cpuinfo_x86 prev_info;
>  
>  	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
> @@ -418,26 +412,47 @@ static int microcode_reload_late(void)
>  	 */
>  	store_cpu_caps(&prev_info);
>  
> -	ret = stop_machine_cpuslocked(__reload_late, NULL, cpu_online_mask);
> +	stop_machine_cpuslocked(ucode_load_cpus_stopped, NULL, cpu_online_mask);
> +
> +	/* Analyze the results */
> +	for_each_cpu_and(cpu, cpu_present_mask, &cpus_booted_once_mask) {
> +		switch (per_cpu(ucode_ctrl.result, cpu)) {
> +		case UCODE_UPDATED:	updated++; break;
> +		case UCODE_TIMEOUT:	timedout++; break;
> +		case UCODE_OK:		siblings++; break;
> +		default:		failed++; break;
> +		}

Align vertically.

> +	}
>  
>  	if (microcode_ops->finalize_late_load)
> -		microcode_ops->finalize_late_load(ret);
> +		microcode_ops->finalize_late_load(!updated);
>  
> -	if (!ret) {
> -		pr_info("Reload succeeded, microcode revision: 0x%x -> 0x%x\n",
> -			old, boot_cpu_data.microcode);
> -		microcode_check(&prev_info);
> -		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> -	} else {
> -		pr_info("Reload failed, current microcode revision: 0x%x\n",
> -			boot_cpu_data.microcode);
> +	if (!updated) {
> +		/* Nothing changed. */
> +		if (!failed && !timedout)
> +			return 0;
> +		pr_err("Microcode update failed: %u CPUs failed %u CPUs timed out\n",
> +		       failed, timedout);
> +		return -EIO;
>  	}
> -	return ret;
> +
> +	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> +	pr_info("Microcode load: updated on %u primary CPUs with %u siblings\n", updated, siblings);
> +	if (failed || timedout) {
> +		pr_err("Microcode load incomplete. %u CPUs timed out or failed\n",
> +		       num_online_cpus() - (updated + siblings));
> +	}
> +	pr_info("Microcode revision: 0x%x -> 0x%x\n", old_rev, boot_cpu_data.microcode);

You don't need "Microcode" in those strings - the pr_info has already
"microcode:" as prefix.

> +	microcode_check(&prev_info);
> +
> +	return updated + siblings == num_online_cpus() ? 0 : -EIO;
>  }
>  
>  /*
> - *  Ensure that all required CPUs which are present and have been booted
> - *  once are online.
> + * This function does two things:
> + *
> + * 1) Ensure that all required CPUs which are present and have been booted
> + *    once are online.
>   *
>   *    To pass this check, all primary threads must be online.
>   *
> @@ -448,9 +463,12 @@ static int microcode_reload_late(void)
>   *    behaviour is undefined. The default play_dead() implementation on
>   *    modern CPUs is using MWAIT, which is also not guaranteed to be safe
>   *    against a microcode update which affects MWAIT.
> + *
> + * 2) Initialize the per CPU control structure
>   */
> -static bool ensure_cpus_are_online(void)
> +static bool ucode_setup_cpus(void)

s/ucode_//

>  {
> +	struct ucode_ctrl ctrl = { .result = -1, };
>  	unsigned int cpu;
>  
>  	for_each_cpu_and(cpu, cpu_present_mask, &cpus_booted_once_mask) {

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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