linux-kernel - [PATCH 3/6] x86/microcode: Refactor platform ID enumeration into a helper

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Message-Id: <20260119195053.E0850F99@davehans-spike.ostc.intel.com>
Date: Mon, 19 Jan 2026 11:50:53 -0800
From: Dave Hansen <dave.hansen@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: sohil.mehta@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jon Kohler <jon@...anix.com>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>, Thomas Gleixner <tglx@...nel.org>, Tony Luck <tony.luck@...el.com>, x86@...nel.org
Subject: [PATCH 3/6] x86/microcode: Refactor platform ID enumeration into a helper


From: Dave Hansen <dave.hansen@...ux.intel.com>

The only code that cares about the platform ID is the microcode update
code itself. To facilitate storing the platform ID in a more generic
place and using it outside of the microcode update itself, put the
enumeration into a helper function in a header. Mirror
intel_get_microcode_revision()'s naming and location.

But, moving away from intel_collect_cpu_info() means that the model
and family information in CPUID is not readily available. Just call
CPUID again.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: x86@...nel.org
Cc: Jon Kohler <jon@...anix.com>
---

 b/arch/x86/include/asm/microcode.h      |   31 +++++++++++++++++++++++++++++++
 b/arch/x86/kernel/cpu/microcode/intel.c |   10 +---------
 2 files changed, 32 insertions(+), 9 deletions(-)

diff -puN arch/x86/include/asm/microcode.h~refactor-get-processor-flags arch/x86/include/asm/microcode.h
--- a/arch/x86/include/asm/microcode.h~refactor-get-processor-flags	2026-01-19 11:38:08.775892390 -0800
+++ b/arch/x86/include/asm/microcode.h	2026-01-19 11:38:08.783892696 -0800
@@ -2,7 +2,9 @@
 #ifndef _ASM_X86_MICROCODE_H
 #define _ASM_X86_MICROCODE_H
 
+#include <asm/cpu.h>
 #include <asm/msr.h>
+#include <asm/intel-family.h>
 
 struct cpu_signature {
 	unsigned int sig;
@@ -75,6 +77,35 @@ static inline u32 intel_get_microcode_re
 
 	return rev;
 }
+
+/*
+ * Use CPUID to generate a "vfm" value. Useful
+ * before 'cpuinfo_x86' structures are populated.
+ */
+static inline u32 intel_cpuid_vfm(void)
+{
+	u32 eax   = cpuid_eax(1);
+	u32 fam   = x86_family(eax);
+	u32 model = x86_model(eax);
+
+	return IFM(fam, model);
+}
+
+static inline u32 intel_get_platform_id(void)
+{
+	unsigned int val[2];
+
+	/*
+	 * This can be called early. Use CPUID directly to
+	 * generate the VFM value for this CPU.
+	 */
+	if (intel_cpuid_vfm() < INTEL_PENTIUM_III_DESCHUTES)
+		return 0;
+
+	/* get processor flags from MSR 0x17 */
+	native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
+	return 1 << ((val[1] >> 18) & 7);
+}
 #endif /* !CONFIG_CPU_SUP_INTEL */
 
 bool microcode_nmi_handler(void);
diff -puN arch/x86/kernel/cpu/microcode/intel.c~refactor-get-processor-flags arch/x86/kernel/cpu/microcode/intel.c
--- a/arch/x86/kernel/cpu/microcode/intel.c~refactor-get-processor-flags	2026-01-19 11:38:08.780892582 -0800
+++ b/arch/x86/kernel/cpu/microcode/intel.c	2026-01-19 11:38:08.783892696 -0800
@@ -123,16 +123,8 @@ static inline unsigned int exttable_size
 void intel_collect_cpu_info(struct cpu_signature *sig)
 {
 	sig->sig = cpuid_eax(1);
-	sig->pf = 0;
 	sig->rev = intel_get_microcode_revision();
-
-	if (IFM(x86_family(sig->sig), x86_model(sig->sig)) >= INTEL_PENTIUM_III_DESCHUTES) {
-		unsigned int val[2];
-
-		/* get processor flags from MSR 0x17 */
-		native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
-		sig->pf = 1 << ((val[1] >> 18) & 7);
-	}
+	sig->pf  = intel_get_platform_id();
 }
 EXPORT_SYMBOL_GPL(intel_collect_cpu_info);
 
_