From:   Thomas Gleixner <tglx@linutronix.de>
To:     David Woodhouse <dwmw2@infradead.org>,
        Usama Arif <usama.arif@bytedance.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>
Cc:     Kim Phillips <kim.phillips@amd.com>, arjan@linux.intel.com,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com,
        paulmck@kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de,
        hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com,
        "Limonciello, Mario" <Mario.Limonciello@amd.com>,
        Piotr Gorski <piotrgorski@cachyos.org>
Subject: Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
In-Reply-To: <e7036423216287e86eab4daf9dd1acdaecdd2b49.camel@infradead.org>
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Date:   Wed, 22 Feb 2023 10:46:25 +0100
Message-ID: <87cz62m3ri.ffs@tglx>
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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