linux-kernel - Re: [External] Re: [PATCH v7 0/9] Parallel CPU bringup for x86

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Date:   Thu, 09 Feb 2023 10:06:55 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Usama Arif <usama.arif@...edance.com>, paulmck@...nel.org,
        tglx@...utronix.de
Cc:     kim.phillips@....com, arjan@...ux.intel.com, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        x86@...nel.org, pbonzini@...hat.com, 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 v7 0/9] Parallel CPU bringup for x86_64

On Thu, 2023-02-09 at 09:49 +0000, Usama Arif wrote:
> 
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1080,6 +1080,7 @@ wakeup_cpu_via_init_nmi(int cpu, unsigned long 
> start_ip, int apicid,
>                                            wakeup_cpu0_nmi, 0, "wake_cpu0");
> 
>          if (!boot_error) {
> +               initial_gs = per_cpu_offset(cpu);

That's for 64-bit.

>                  enable_start_cpu0 = 1;
>                  *cpu0_nmi_registered = 1;
>                  id = apic->dest_mode_logical ? cpu0_logical_apicid :
> apicid;
> @@ -1188,10 +1189,14 @@ static int do_boot_cpu(int apicid, int cpu, 
> struct task_struct *idle,
>                  boot_error = apic->wakeup_secondary_cpu_64(apicid, 
> start_ip);
>          else if (apic->wakeup_secondary_cpu)
>                  boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);
> -       else
> +       else {
> +               if(!cpu) {
> +                       early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
> +                       initial_stack  = idle->thread.sp;
> +               }

And that's 32-bit.

These were previously done in common_cpu_up() or do_boot_cpu(), which
means they were done not only for the wakeup_cpu_via_init_nmi() code
path, but also when we call apic->wakeup_secondary_cpu() (or _64()) for
the esoteric UV/NumaConnect machines.

Thanks for diagnosing it so quickly; I'll work up a subtly different
fix.

>                  boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
>                                                       cpu0_nmi_registered);
> -
> +       }
>          return boot_error;
>   }
> 


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