Re: [PATCH v4 1/4] x86/microcode: Refactor platform ID enumeration into a helper

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

On Wed, Mar 04, 2026 at 10:10:18AM -0800, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> 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.
> 
> Also note that the PII is weird. It does not really have a platform
> ID because it doesn't even have the MSR. Just consider it to be
> platform ID 0. Instead of saying >=PII, say <=PII. The PII is the
				     ^
				     I think you meant PIII here?

> real oddball here being the only CPU with Linux microcode updates
> but no platform ID. It's worth calling it out by name.
> 
> This does subtly change the sig->pf for the PII though from 0x0
> to 0x1. Make up for that by ignoring sig->pf when the microcode
> update platform mask is 0x0.
> 
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
> Cc: Thomas Gleixner <tglx@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
> Cc: x86@kernel.org
> Cc: Jon Kohler <jon@nutanix.com>
> 
> --
> 
> Changes from v3:
>  * Handle the empty platform mask on the PII
> 
> ---
> 
>  b/arch/x86/kernel/cpu/microcode/intel.c |   53 +++++++++++++++++++++++++-------
>  1 file changed, 42 insertions(+), 11 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	2026-03-04 09:19:02.438748485 -0800
> +++ b/arch/x86/kernel/cpu/microcode/intel.c	2026-03-04 09:19:02.441748599 -0800
> @@ -120,19 +120,43 @@ 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);

Nit, is s/eax/sig/ more clear?

	u32 sig   = cpuid_eax(1);
	u32 fam   = x86_family(sig);
	u32 model = x86_model(sig);

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>