Re: [PATCH 02/20] x86/mce: Define mce_setup() helpers for global and per-CPU fields

[Yazen Ghannam]

On 11/22/2023 1:24 PM, Borislav Petkov wrote:
> On Sat, Nov 18, 2023 at 01:32:30PM -0600, Yazen Ghannam wrote:
> > +void mce_setup_global(struct mce *m)
>
> We usually call those things "common":
>
> mce_setup_common().
>
> > +{
> > +	memset(m, 0, sizeof(struct mce));
> > +
> > +	m->cpuid	= cpuid_eax(1);
> > +	m->cpuvendor	= boot_cpu_data.x86_vendor;
> > +	m->mcgcap	= __rdmsr(MSR_IA32_MCG_CAP);
> > +	/* need the internal __ version to avoid deadlocks */
> > +	m->time		= __ktime_get_real_seconds();
> > +}
> > +
> > +void mce_setup_per_cpu(struct mce *m)
>
> And call this
>
> 	mce_setup_for_cpu(unsigned int cpu, struct mce *m);
>
> so that it doesn't look like some per_cpu helper.
>
> And yes, you should supply the CPU number as an argument. Because
> otherwise, when you look at your next change:
>
>
> +       mce_setup_global(&m);
> +       m.cpu = m.extcpu = cpu;
> +       mce_setup_per_cpu(&m);
>
> This contains the "hidden" requirement that m.extcpu happens *always*
> *before* the mce_setup_per_cpu() call and that is flaky and error prone.
>
> So make that:
>
> 	mce_setup_common(&m);
> 	mce_setup_for_cpu(m.extcpu, &m);
>
> and do m.cpu = m.extcpu = cpu inside the second function.
>
> And then it JustWorks(tm) and you can't "forget" assigning m.extcpu and
> there's no subtlety.
>
> Ok?

Yep, understood. Thanks!

-Yazen