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 16:14:53 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>,
        Usama Arif <usama.arif@...edance.com>, 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,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>
Subject: Re: [PATCH v14 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary
 CPUs in parallel

On Sat, Mar 11 2023 at 09:55, David Woodhouse wrote:
> On Sat, 2023-03-11 at 10:54 +0200, Thomas Gleixner wrote:
> I think I'll do it with a 'bool unpoison' argument to
> idle_thread_get(). Or just make it unconditional; they're idempotent
> anyway and cheap enough? Kind of weird to be doing it from finish_cpu()
> though, so I'll probably stick with the argument.

Eew.

> ....*types*....
>
> Erm, there are circumstances (!CONFIG_GENERIC_SMP_IDLE_THREAD) when
> idle_thread_get() just unconditionally returns NULL.
>
> At first glance, it doesn't look like scs_task_reset() copes with being
> passed a NULL. Am I missing something?

Shadow call stacks are only enabled by arm64 today, and that uses
the generic idle threads.

Thanks,

        tglx