linux-kernel - Re: [External] Re: [PATCH v12 00/11] Parallel CPU bringup for x86

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Date:   Mon, 27 Feb 2023 15:29:27 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Usama Arif <usama.arif@...edance.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        tglx@...utronix.de, kim.phillips@....com, brgerst@...il.com
Cc:     piotrgorski@...hyos.org, arjan@...ux.intel.com, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        x86@...nel.org, pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com
Subject: Re: [External] Re: [PATCH v12 00/11] Parallel CPU bringup for x86_64

On Mon, 2023-02-27 at 06:14 +0000, Usama Arif wrote:
> 
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 17bdd6122dca..5d709aa67df4 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -273,7 +273,11 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, 
> SYM_L_GLOBAL)
>          cmpl    (%rbx,%rcx,4), %edx
>          jz      .Lsetup_cpu
>          inc     %ecx
> +#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
> +       cmpl    $NR_CPUS, %ecx
> +#else
>          cmpl    nr_cpu_ids(%rip), %ecx
> +#endif
>          jb      .Lfind_cpunr
> 
>          /*  APIC ID not found in the table. Drop the trampoline lock
> and bail. */

The whitespace looks dodgy there but maybe that's just your mail client?

Given this code is already in #ifdef CONFIG_SMP, can NR_CPUS be 1?

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