linux-kernel - Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86

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Message-ID: <87cz62m3ri.ffs@tglx>
Date:   Wed, 22 Feb 2023 10:46:25 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>,
        Usama Arif <usama.arif@...edance.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Kim Phillips <kim.phillips@....com>, 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,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        Piotr Gorski <piotrgorski@...hyos.org>
Subject: Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

On Wed, Feb 22 2023 at 08:19, David Woodhouse wrote:
> But the BSP/CPU0 is different. It hasn't actually been taken offline,
> and its idle thread context is still in cpu_startup_entry(CPUHP_ONLINE)
> which got called from rest_init().
>
> In testing I probably got away with it because we're only using the
> *top* of the stack, don't use anything of the red zone, and thus don't
> actually bother the true idle thread which is never going to return.

:)

> But I don't think it's correct; we really ought to have that temp_stack
> unless we're going to refactor the wakeup_64 code to *become* the idle
> thread just as startup_secondary() does, and *schedule* to the context
> that was saved in the suspend code.

And thereby messing up the scheduler state...

Thanks,

        tglx