linux-kernel - Re: [PATCH v9 0/8] Parallel CPU bringup for x86

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Message-ID: <ee0d0d971a3095d6a1e96ad4f1ba32d2@natalenko.name>
Date:   Tue, 21 Feb 2023 09:25:08 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Kim Phillips <kim.phillips@....com>, tglx@...utronix.de,
        Usama Arif <usama.arif@...edance.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,
        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,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        Piotr Gorski <piotrgorski@...hyos.org>
Subject: Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

On 21.02.2023 09:17, David Woodhouse wrote:
> On Tue, 2023-02-21 at 09:05 +0100, Oleksandr Natalenko wrote:
>> 
>> Please see here: http://ix.io/4oLm
> 
> Was that just for one CPU? Can we have them all please?
> 
> The interesting part is the line starting 00000001. We're looking at
> the top 8 bits of EBX:
> 
> Leaf     Subleaf    EAX            EBX            ECX            EDX
> 00000000 00000000:  00000010 ....  68747541 Auth  444d4163 cAMD  
> 69746e65 enti
> 00000001 00000000:  00a20f12 ....  00200800 .. .  7ef8320b .2.~  
> 178bfbff ....
>                                    ↑↑
> 
> So the first CPU is CPU0. Could have told you that... what about the 
> others? :)

Right, sorry. Here it is: http://ix.io/4oLq

> If anyone can reproduce this with a serial port, can you try this?
> 
> From 98ad11d0fb88f081f49f7b1496420dbfbeff8833 Mon Sep 17 00:00:00 2001
> From: David Woodhouse <dwmw@...zon.co.uk>
> Date: Sat, 4 Feb 2023 15:20:24 +0000
> Subject: [PATCH] parallel debug
> 
> ---
>  arch/x86/kernel/head_64.S | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 0e4e53d231db..da7f4d2d9951 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -281,6 +281,15 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, 
> SYM_L_GLOBAL)
> 
>  .Lsetup_AP:
>  	/* EDX contains the APIC ID of the current CPU */
> +#if 1
> +	/* Test hack: Print APIC ID and then CPU# when we find it. */
> +	mov	%edx, %ecx
> +	mov	%edx, %eax
> +	addb	$'A', %al
> +	mov	$0x3f8, %dx
> +	outb    %al, %dx
> +	mov	%ecx, %edx
> +#endif
>  	xorq	%rcx, %rcx
>  	leaq	cpuid_to_apicid(%rip), %rbx
> 
> @@ -302,6 +311,14 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, 
> SYM_L_GLOBAL)
> 
>  .Linit_cpu_data:
>  	/* Get the per cpu offset for the given CPU# which is in ECX */
> +#if 1
> +	mov	%rcx, %rax
> +	shr	$3, %rax
> +	addb	$'a', %al
> +
> +	mov	$0x3f8, %dx
> +	outb    %al, %dx
> +#endif
>  	leaq	__per_cpu_offset(%rip), %rbx
>  	movq	(%rbx,%rcx,8), %rbx
>  	/* Save it for GS BASE setup */

-- 
   Oleksandr Natalenko (post-factum)