linux-kernel - Re: [PATCH v5 07/20] x86/mce: Reorder __mcheck_cpu_init

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Message-ID: <20250901170741.GCaLXS3bUdUPksnMs8@fat_crate.local>
Date: Mon, 1 Sep 2025 19:07:41 +0200
From: Borislav Petkov <bp@...en8.de>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: x86@...nel.org, Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Smita.KoralahalliChannabasappa@....com,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v5 07/20] x86/mce: Reorder __mcheck_cpu_init_generic()
 call

On Mon, Aug 25, 2025 at 05:33:04PM +0000, Yazen Ghannam wrote:
> Move __mcheck_cpu_init_generic() after __mcheck_cpu_init_prepare_banks()
> so that MCA is enabled after the first MCA polling event.
> 
> This brings the MCA init flow closer to what is described in the x86 docs.
> 
> The AMD PPRs say
>   "The operating system must initialize the MCA_CONFIG registers prior
>   to initialization of the MCA_CTL registers.
> 
>   The MCA_CTL registers must be initialized prior to enabling the error
>   reporting banks in MCG_CTL".
> 
> However, the Intel SDM "Machine-Check Initialization Pseudocode" says
> MCG_CTL first then MCi_CTL.
> 
> But both agree that CR4.MCE should be set last.
> 
> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> ---
> 
> Notes:
>     Link:
>     https://lore.kernel.org/r/52a37afe-c41b-4f20-bbdc-bddc3ae26260@suse.com
>     
>     v4->v5:
>     * New in v5.
> 
>  arch/x86/kernel/cpu/mce/core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 0326fbb83adc..9cbf9e8c8060 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -2272,9 +2272,9 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
>  
>  	mca_cfg.initialized = 1;
>  
> -	__mcheck_cpu_init_generic();
>  	__mcheck_cpu_init_vendor(c);
>  	__mcheck_cpu_init_prepare_banks();
> +	__mcheck_cpu_init_generic();

With that flow we have now:

	1. MCA_CTL
	2. CR4.MCE
	3. MCG_CTL

So this is nothing like in the commit message above and the MC*_CTL flow is
not what the SDM suggests and CR4.MCE is not last.

So what's the point even here?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette