[PATCH 1/4] x86/microcode: Refactor platform ID enumeration into a helper

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Today, 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. 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.

Note that the microcode header is a mask of supported platform IDs.
Only stick the ID part in the helper. Leave the 1<<id part in the
microcode handling.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Jon Kohler <jon@xxxxxxxxxxx>
---

 b/arch/x86/kernel/cpu/microcode/intel.c |   40 ++++++++++++++++++++++++--------
 1 file changed, 31 insertions(+), 9 deletions(-)

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	2026-02-13 15:51:00.488332290 -0800
+++ b/arch/x86/kernel/cpu/microcode/intel.c	2026-02-13 15:51:00.492332445 -0800
@@ -120,19 +120,41 @@ static inline unsigned int exttable_size
 	return et->count * EXT_SIGNATURE_SIZE + EXT_HEADER_SIZE;
 }
 
+/*
+ * Use CPUID to generate a "vfm" value. Useful
+ * before 'cpuinfo_x86' structures are populated.
+ */
+static 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 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 (val[1] >> 18) & 7;
+}
+
 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  = 1 << intel_get_platform_id();
 }
 EXPORT_SYMBOL_GPL(intel_collect_cpu_info);
 
_