From:   Thomas Gleixner <tglx@linutronix.de>
To:     Usama Arif <usama.arif@bytedance.com>, dwmw2@infradead.org,
        kim.phillips@amd.com, brgerst@gmail.com
Cc:     piotrgorski@cachyos.org, oleksandr@natalenko.name,
        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,
        David Woodhouse <dwmw@amazon.co.uk>,
        Usama Arif <usama.arif@bytedance.com>,
        "Guilherme G . Piccoli" <gpiccoli@igalia.com>
Subject: Re: [PATCH v14 10/12] x86/smpboot: Send INIT/SIPI/SIPI to secondary
 CPUs in parallel
In-Reply-To: <20230308171328.1562857-11-usama.arif@bytedance.com>
References: <20230308171328.1562857-1-usama.arif@bytedance.com>
 <20230308171328.1562857-11-usama.arif@bytedance.com>
Date:   Sat, 11 Mar 2023 10:54:58 +0200
Message-ID: <87y1o3acrh.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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