linux-kernel - Re: [RFC PATCH 06/15] x86/microcode: Update the Intel processor flag scan check

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Message-ID: <1f3524fb-079d-463d-b6fa-68fda2d5cd22@intel.com>
Date: Sat, 21 Dec 2024 07:46:33 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...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>,
 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: [RFC PATCH 06/15] x86/microcode: Update the Intel processor flag
 scan check

On 12/20/24 13:37, Sohil Mehta wrote:
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -74,7 +74,8 @@ void intel_collect_cpu_info(struct cpu_signature *sig)
>  	sig->pf = 0;
>  	sig->rev = intel_get_microcode_revision();
>  
> -	if (x86_model(sig->sig) >= 5 || x86_family(sig->sig) > 6) {
> +	/* TODO: Simplify this using a VFM check? */
> +	if ((x86_family(sig->sig) == 6 && x86_model(sig->sig) >= 5) || x86_family(sig->sig) > 6) {
>  		unsigned int val[2];
>  
>  		/* get processor flags from MSR 0x17 */

I suspect this code is kinda bogus in the first place. sig->sig is just
cpuid_eax(1) and:

	void cpu_detect(struct cpuinfo_x86 *c)
	{
		...
                cpuid(0x00000001, &tfms, &misc, &junk, &cap0);
                c->x86          = x86_family(tfms);

So I'm not quite sure why this code feels the need to redo CPUID and
re-parse it. Other bits of the microcode update may need 'sig' in its
unparsed form to conveniently compare with parts of the microcode image,
but that's no reason to re-parse it too.

I _think_ this code can just use good old cpu_data() and the existing
VFM mechanism.