linux-kernel - Re: [PATCH v14 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel

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Date:   Sat, 11 Mar 2023 10:54:58 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Usama Arif <usama.arif@...edance.com>, dwmw2@...radead.org,
        kim.phillips@....com, brgerst@...il.com
Cc:     piotrgorski@...hyos.org, oleksandr@...alenko.name,
        arjan@...ux.intel.com, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com,
        David Woodhouse <dwmw@...zon.co.uk>,
        Usama Arif <usama.arif@...edance.com>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>
Subject: Re: [PATCH v14 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary
 CPUs in parallel

On Wed, Mar 08 2023 at 17:13, Usama Arif wrote:
>  
> +/* Bringup step one: Send INIT/SIPI to the target AP */
> +static int native_cpu_kick(unsigned int cpu)
> +{
> +	return do_cpu_up(cpu, idle_thread_get(cpu));

This idle_thread_get() is not sufficient. bringup_cpu() does:

	struct task_struct *idle = idle_thread_get(cpu);

	/*
	 * Reset stale stack state from the last time this CPU was online.
	 */
	scs_task_reset(idle);
	kasan_unpoison_task_stack(idle);

But with this new model neither the shadow stack gets reset nor the
kasan unpoisoning happens _before_ the to be kicked CPU starts
executing.

That needs a new function which does the get() and the above.

Thanks,

        tglx