linux-kernel - Re: [PATCH v2 06/10] x86/mce: Convert multiple if () statements into a switch() statement

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Message-ID: <1a56307f-f280-4ce6-878e-98923ddc2102@intel.com>
Date: Thu, 24 Oct 2024 15:18:56 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, "Luck, Tony" <tony.luck@...el.com>,
 "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>
Cc: "bp@...en8.de" <bp@...en8.de>, "tglx@...utronix.de" <tglx@...utronix.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "mingo@...hat.com" <mingo@...hat.com>, "hpa@...or.com" <hpa@...or.com>,
 "x86@...nel.org" <x86@...nel.org>,
 "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 06/10] x86/mce: Convert multiple if () statements into
 a switch() statement

On 10/24/24 14:31, Sohil Mehta wrote:
> @@ -1924,6 +1924,10 @@ static void apply_quirks_intel(struct cpuinfo_x86 *c)
>         struct mce_bank *mce_banks = this_cpu_ptr(mce_banks_array);
>         struct mca_config *cfg = &mca_cfg;
> 
> +       /* Older CPUs (prior to family 6) don't need quirks. */
> +       if (c->x86_vfm < INTEL_PENTIUM_PRO)
> +               return;

In case anyone grumbles, this is one of those expressions that's not
perfect, but I think it's quite good enough in practice.

It wouldn't work if we ever (for instance) moved 'vendor' to be less
significant bits than 'model'.  Or on a CPU that claimed to be family=6
but model=0.  But Intel never (as far as I know) sold a CPU like that,
so it's probably only possible in a VM where these checks are rather
worthless anyway.

In short, I think >=INTEL_PENTIUM_PRO is a great check that can mean
"family 6 or later" almost anywhere.