linux-kernel - Re: [PATCH v2 13/17] x86/pat: Replace Intel x86

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Message-ID: <ea2d3068-538f-4e94-b1be-765e06e0edcb@intel.com>
Date: Tue, 11 Feb 2025 13:42:52 -0800
From: Sohil Mehta <sohil.mehta@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, <x86@...nel.org>, Dave Hansen
	<dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>
CC: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim
	<namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, "Alexander
 Shishkin" <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
	"Kan Liang" <kan.liang@...ux.intel.com>, Thomas Gleixner
	<tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, "H . Peter Anvin"
	<hpa@...or.com>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown
	<lenb@...nel.org>, Andy Lutomirski <luto@...nel.org>, Viresh Kumar
	<viresh.kumar@...aro.org>, Fenghua Yu <fenghua.yu@...el.com>, Jean Delvare
	<jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>, Zhang Rui
	<rui.zhang@...el.com>, Andrew Cooper <andrew.cooper3@...rix.com>, David
 Laight <david.laight.linux@...il.com>, <linux-perf-users@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH v2 13/17] x86/pat: Replace Intel x86_model checks with VFM
 ones

On 2/11/2025 1:09 PM, Dave Hansen wrote:
> On 2/11/25 11:44, Sohil Mehta wrote:
>> +	if (c->x86_vendor == X86_VENDOR_INTEL &&
>> +	    ((c->x86_vfm >= INTEL_PENTIUM_PRO && c->x86_vfm <= INTEL_PENTIUM_M_DOTHAN) ||
>> +	    (c->x86_vfm >= INTEL_P4_WILLAMETTE && c->x86_vfm <= INTEL_P4_CEDARMILL))) {
> 
> Since these are both closed checks and not open-ended, is the
> 
> 	if (c->x86_vendor == X86_VENDOR_INTEL &&
> 
> bit needed or superfluous?
> 

You are right, since it is close ended on both sides we should be able
to remove the X86_VENDOR_INTEL.

I was thinking if we should leave it there to avoid confusion. But,
INTEL_* in the VFM string is a good enough hint that the checks are
Intel specific. Also, it's not like this check is going to be modified
frequently.

> Also, super nit, can you vertically align the two range checks, please?
> 
> 	    ((c->x86_vfm >= INTEL_PENTIUM_PRO   && c->x86_vfm <=
> INTEL_PENTIUM_M_DOTHAN) ||
> 	     (c->x86_vfm >= INTEL_P4_WILLAMETTE && c->x86_vfm <=
> INTEL_P4_CEDARMILL))) {
> 
>