Re: [PATCH v2 06/10] x86/mce: Convert multiple if () statements into a switch() statement

[Sohil Mehta]

On 10/21/2024 10:51 AM, Luck, Tony wrote:
>> But looking at the prior or the later checks, I see the '<' operator
>> used directly on platform names. So, the new check seems inline with
>> that i.e. in this case, any model or family after the said platform
>> supports MCE broadcasting.
> 
> Intel model number allocation policies aren't necessarily sequential.

Model numbers are assumed to be sequential at least within family 6.

if ((c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xe)) &&
	cfg->monarch_timeout < 0)

There is another check in early_init_intel() which does this:

	if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
		rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);


> So range checks need to be used with caution. They should be safe
> enough when done to simplify code that checks very old models.
> 

...

> Range checks across families may be even more problematic. 

I agree. Maybe we should avoid range checks across families altogether
forward (>) or backward (<).

For example, does the following change from Qiuxu, unintentionally
become applicable to Quark CPUs with family -> 5?


>         /*
>          * There are also broken BIOSes on some Pentium M and
>          * earlier systems:
>          */
> -       if (c->x86 == 6 && c->x86_model <= 13 && cfg->bootlog < 0)
> +       if (c->x86_vfm < INTEL_CORE_YONAH && cfg->bootlog < 0)
>                 cfg->bootlog = 0;