linux-kernel - Re: [patch V3 23/30] x86/microcode: Provide new control functions

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Message-ID: <20230924065824.GNZQ/eEKAO8IaCcUJU@fat_crate.local>
Date:   Sun, 24 Sep 2023 08:58:24 +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 23/30] x86/microcode: Provide new control functions

On Tue, Sep 12, 2023 at 09:58:20AM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The current all in one code is unreadable and really not suited for adding
> future features like uniform loading with package or system scope.
> 
> Provide a set of new control functions which split the handling of the
> primary and secondary CPUs. These will replace the current rendevouz all in

rendezvous

In the comments below too.

> one function in the next step. This is intentionally a separate change
> because diff makes an complete unreadable mess otherwise.
> 
> So the flow separates the primary and the secondary CPUs into their own
> functions, which use the control field in the per CPU ucode_ctrl struct.
> 
>    primary()			secondary()
>     wait_for_all()		 wait_for_all()
>     apply_ucode()		 wait_for_release()
>     release()			 apply_ucode()
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>  arch/x86/kernel/cpu/microcode/core.c |   86 +++++++++++++++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
> ---
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -357,6 +357,92 @@ static bool wait_for_cpus(atomic_t *cnt)
>  	return false;
>  }
>  
> +static bool wait_for_ctrl(void)
> +{
> +	unsigned int timeout;
> +
> +	for (timeout = 0; timeout < USEC_PER_SEC; timeout++) {
> +		if (this_cpu_read(ucode_ctrl.ctrl) != SCTRL_WAIT)
> +			return true;
> +		udelay(1);
> +		if (!(timeout % 1000))
> +			touch_nmi_watchdog();
> +	}
> +	return false;
> +}
> +
> +static __maybe_unused void ucode_load_secondary(unsigned int cpu)

s/ucode_//

ucode_load_primary() too.

> +{
> +	unsigned int ctrl_cpu = this_cpu_read(ucode_ctrl.ctrl_cpu);
> +	enum ucode_state ret;
> +
> +	/* Initial rendevouz to ensure that all CPUs have arrived */
> +	if (!wait_for_cpus(&late_cpus_in)) {
> +		pr_err_once("Microcode load: %d CPUs timed out\n",

Make that look like "microcode: Late loading: ..."

And I think we should use "Late loading" or similar prefix for all those
operations here so that it is easily greppable in the logs.

> +			    atomic_read(&late_cpus_in) - 1);
> +		this_cpu_write(ucode_ctrl.result, UCODE_TIMEOUT);
> +		return;
> +	}
> +
> +	/*
> +	 * Wait for primary threads to complete. If one of them hangs due
> +	 * to the update, there is no way out. This is non-recoverable
> +	 * because the CPU might hold locks or resources and confuse the
> +	 * scheduler, watchdogs etc. There is no way to safely evacuate the
> +	 * machine.
> +	 */
> +	if (!wait_for_ctrl())
> +		panic("Microcode load: Primary CPU %d timed out\n", ctrl_cpu);
> +
> +	/*
> +	 * If the primary succeeded then invoke the apply() callback,
> +	 * otherwise copy the state from the primary thread.
> +	 */
> +	if (this_cpu_read(ucode_ctrl.ctrl) == SCTRL_APPLY)
> +		ret = microcode_ops->apply_microcode(cpu);
> +	else
> +		ret = per_cpu(ucode_ctrl.result, ctrl_cpu);
> +
> +	this_cpu_write(ucode_ctrl.result, ret);
> +	this_cpu_write(ucode_ctrl.ctrl, SCTRL_DONE);
> +}
> +
> +static __maybe_unused void ucode_load_primary(unsigned int cpu)
> +{
> +	struct cpumask *secondaries = topology_sibling_cpumask(cpu);
> +	enum sibling_ctrl ctrl;
> +	enum ucode_state ret;
> +	unsigned int sibling;
> +
> +	/* Initial rendevouz to ensure that all CPUs have arrived */
> +	if (!wait_for_cpus(&late_cpus_in)) {
> +		this_cpu_write(ucode_ctrl.result, UCODE_TIMEOUT);
> +		pr_err_once("Microcode load: %d CPUs timed out\n",
> +			    atomic_read(&late_cpus_in) - 1);
> +		return;
> +	}
> +
> +	ret = microcode_ops->apply_microcode(cpu);
> +	this_cpu_write(ucode_ctrl.result, ret);
> +	this_cpu_write(ucode_ctrl.ctrl, SCTRL_DONE);

Do that update...

> +
> +	/*
> +	 * If the update was successful, let the siblings run the apply()
> +	 * callback. If not, tell them it's done. This also covers the
> +	 * case where the CPU has uniform loading at package or system
> +	 * scope implemented but does not advertise it.
> +	 */
> +	if (ret == UCODE_UPDATED || ret == UCODE_OK)
> +		ctrl = SCTRL_APPLY;
> +	else
> +		ctrl = SCTRL_DONE;

... here, after having checked ret.

> +
> +	for_each_cpu(sibling, secondaries) {
> +		if (sibling != cpu)
> +			per_cpu(ucode_ctrl.ctrl, sibling) = ctrl;
> +	}
> +}
> +
>  static int ucode_load_cpus_stopped(void *unused)
>  {
>  	int cpu = smp_processor_id();
> 

-- 
Regards/Gruss,
    Boris.

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