linux-kernel - Re: [PATCH] x86/MCE: Get microcode revision from cpu_data instead of boot_cpu

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Message-ID: <ZWos70EKhlAl2VPb@agluck-desk3>
Date:   Fri, 1 Dec 2023 10:58:55 -0800
From:   Tony Luck <tony.luck@...el.com>
To:     Filippo Sironi <sironi@...zon.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-edac@...g.kernel.org, bp@...en8.de, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, hpa@...or.com
Subject: Re: [PATCH] x86/MCE: Get microcode revision from cpu_data instead of
 boot_cpu_data

On Fri, Dec 01, 2023 at 11:23:27AM +0000, Filippo Sironi wrote:
> Commit fa94d0c6e0f3 ("x86/MCE: Save microcode revision in machine check
> records") extended MCE entries to report the microcode revision taken
> from boot_cpu_data. Unfortunately, boot_cpu_data isn't updated on late
> microcode loading, thus making MCE entries slightly incorrect.  Use

This code in intel.c:apply_microcode_late() looks like it tries to update
boot_cpu_data:

466         cpu_data(cpu).microcode  = uci->cpu_sig.rev;
467         if (!cpu)
468                 boot_cpu_data.microcode = uci->cpu_sig.rev;

Is that not working for some reason?

> cpu_data instead, which is updated on late microcode loading. This also
> fixes the corner case in which the microcode revision isn't coherent
> across CPUs (which may happen on late microcode loading failure).

But this does seem a worthwhile change to help diagnose things if late
load is somehow only applied to some subset of CPUs.
> 
> Signed-off-by: Filippo Sironi <sironi@...zon.de>
> ---
>  arch/x86/kernel/cpu/mce/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 7b397370b4d6..e1b033298db0 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -127,7 +127,7 @@ void mce_setup(struct mce *m)
>  	m->apicid = cpu_data(m->extcpu).topo.initial_apicid;
>  	m->mcgcap = __rdmsr(MSR_IA32_MCG_CAP);
>  	m->ppin = cpu_data(m->extcpu).ppin;
> -	m->microcode = boot_cpu_data.microcode;
> +	m->microcode = cpu_data(m->extcpu).microcode;
>  }
>  
>  DEFINE_PER_CPU(struct mce, injectm);
> -- 
> 2.33.0

-Tony