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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Brian Gerst <brgerst@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        David Woodhouse <dwmw@infradead.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
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        Mark Rutland <mark.rutland@arm.com>,
        Sabin Rapan <sabrapan@amazon.com>
Subject: Re: [patch 35/37] x86/smpboot: Support parallel startup of
 secondary CPUs
In-Reply-To: <CAMzpN2hUbYpYrqDL1ViXUWGKGa7mDEG6iHtWEZg9GvrAoRgvKQ@mail.gmail.com>
References: <20230414225551.858160935@linutronix.de>
 <20230414232311.379210081@linutronix.de>
 <CAMzpN2hUbYpYrqDL1ViXUWGKGa7mDEG6iHtWEZg9GvrAoRgvKQ@mail.gmail.com>
Date:   Sat, 15 Apr 2023 23:06:38 +0200
Message-ID: <87mt38yhwh.ffs@tglx>
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On Sat, Apr 15 2023 at 09:22, Brian Gerst wrote:
> On Fri, Apr 14, 2023 at 7:45=E2=80=AFPM Thomas Gleixner <tglx@linutronix.=
de> wrote:
>> @@ -248,10 +311,20 @@ SYM_INNER_LABEL(secondary_startup_64_no_
>>          *
>>          * RDX contains the per-cpu offset
>>          */
>> -       movq    pcpu_hot + X86_current_task(%rdx), %rax
>> -       movq    TASK_threadsp(%rax), %rsp
>> +       movq    pcpu_hot + X86_top_of_stack(%rdx), %rsp
>
> Switching to using pcpu_hot.top_of_stack is ok, but it's not
> completely equivalent.  top_of_stack points to the end of the pt_regs
> structure, while the kernel stack starts below pt_regs even for kernel
> threads.  So you need to subtract PTREGS_SIZE from the stack pointer
> after this.
>
> This change should also be a separate patch.

You're right on both counts.