Message-ID: <541a3e2a-d72e-98f7-bfc6-f64ef65f3043@bytedance.com>
Date:   Thu, 9 Feb 2023 11:45:32 +0000
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Subject: Re: [External] Re: [PATCH v7 0/9] Parallel CPU bringup for x86_64
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To:     David Woodhouse <dwmw2@infradead.org>, paulmck@kernel.org,
        tglx@linutronix.de
Cc:     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, 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
References: <20230207230436.2690891-1-usama.arif@bytedance.com>
 <20230209035300.GA3216394@paulmck-ThinkPad-P17-Gen-1>
 <8e2f03e2-9517-aeb4-df60-b36ef3ff3a75@bytedance.com>
 <f07b371ae2eb11f541c665b488b3d4b6bf1a81b3.camel@infradead.org>
From:   Usama Arif <usama.arif@bytedance.com>
In-Reply-To: <f07b371ae2eb11f541c665b488b3d4b6bf1a81b3.camel@infradead.org>
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On 09/02/2023 11:03, David Woodhouse wrote:
> On Thu, 2023-02-09 at 09:49 +0000, Usama Arif wrote:
>>
>> Its easy to test, just by doing
>> echo 0 > /sys/devices/system/cpu/cpu0/online;
>> echo 1 > /sys/devices/system/cpu/cpu0/online;
> 
> This one also fixes it for me. If we're happy with this approach, I'll
> work it into Thomas's original patch (and hopefully eventually he'll be
> happy enough with it and the commit message that he'll give us his
> Signed-off-by for it.)
> 

Yes, I think its better!

> 
> I could probably add a Co-developed-by: tglx for that first x2apic
> patch in the series too, but then it would *also* need his SoB and I
> didn't want to be owed two, so I just pasted his suggested code and
> didn't credit him.
> 
> 
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 5462464fe3ef..ea6052a97619 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -450,7 +450,16 @@ SYM_CODE_END(secondary_startup_64)
>   SYM_CODE_START(start_cpu0)
>          ANNOTATE_NOENDBR
>          UNWIND_HINT_EMPTY
> -       movq    initial_stack(%rip), %rsp
> +       /* Load the per-cpu base for CPU#0 */
> +       leaq    __per_cpu_offset(%rip), %rbx
> +       movq    (%rbx), %rbx
> +
> +       /* Find the idle task stack */
> +       movq    $idle_threads, %rcx
> +       addq    %rbx, %rcx
> +       movq    (%rcx), %rcx
> +       movq    TASK_threadsp(%rcx), %rsp
> +
>          jmp     .Ljump_to_C_code
>   SYM_CODE_END(start_cpu0)
>   #endif
> 
> I cut and pasted some of that, I'm not entirely sure why we have three
> instructions to do the equivalent of 'movq idle_threads(%ebx), %ecx'
> and may fix that in the original as I work this in.