linux-kernel - Re: [patch 35/37] x86/smpboot: Support parallel startup of secondary CPUs

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Message-ID: <878reh17sj.ffs@tglx>
Date:   Mon, 24 Apr 2023 19:58:36 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Brian Gerst <brgerst@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        David Woodhouse <dwmw@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        linux-csky@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>
Subject: Re: [patch 35/37] x86/smpboot: Support parallel startup of
 secondary CPUs

On Sat, Apr 15 2023 at 23:06, Thomas Gleixner wrote:

> On Sat, Apr 15 2023 at 09:22, Brian Gerst wrote:
>> On Fri, Apr 14, 2023 at 7:45 PM Thomas Gleixner <tglx@...utronix.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.

Actually no. We can't do that as this breaks suspend/resume (again).

/me drops it.