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

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Message-ID: <SJ1PR11MB60832636201CA40AD13C02C1FC432@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Mon, 21 Oct 2024 17:51:28 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Mehta, Sohil" <sohil.mehta@...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

> I am not very familiar with the intricacies of the VFM checks. I did
> take me a few minutes to figure out why the modified code is correct.

Hence my concern :-)

> But looking at the prior or the later checks, I see the '<' operator
> used directly on platform names. So, the new check seems inline with
> that i.e. in this case, any model or family after the said platform
> supports MCE broadcasting.

Intel model number allocation policies aren't necessarily sequential.
So range checks need to be used with caution. They should be safe
enough when done to simplify code that checks very old models.

Range checks across families may be even more problematic. Again
these old checks that assume all future families will not reintroduce
quirks from 20-year-old CPUs should be safe (I hope!!).

But, spoiler alert, Intel is planning to begin use of two families in
parallel. Family 19 (first model Diamond Rapids) is already in
<asm/intel-family.h>). But there are going to be some CPUs
in family 18 too. I'll be surprised if there are any use cases for
ranges that span between families 18 and 19.

-Tony