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

[Dave Hansen]

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.