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SubjectRe: [Patch V1 2/3] x86, mce: Add infrastructure required to support LMCE
Hi Boris

If you got a blank email, sorry about that. Its been a while since i used
mutt and my setup was goofed up probably. Or i might have read your
signature a bit too literally :-)

> > +
> > + if (mca_cfg.lmce_disabled)
> > + return false;
> > +
> > + rdmsrl(MSR_IA32_MCG_CAP, cap);
> > + rdmsrl(MSR_IA32_FEATURE_CONTROL, feature_ctl);
>

> One more thing: You should check MCG_LMCE_P *first* and only read
> MSR_IA32_FEATURE_CONTROL if MCG_LMCE_P is set - otherwise this'll start
> blowing up on older machines which don't sport that new MSR and on kvm.

I did re-organize this to read better in my upcoming post. But in general
reading FEATURE_CONTROL isn't bad. It wont trip on a #GP for e.g.
FEATURE_CONTROL has been around for a while. Only when we set
reserved bits without checking would be bad.
>
> > + lmce_bios_support = ((feature_ctl & (FEATURE_CONTROL_LMCE_BITS)) ==
> > + (FEATURE_CONTROL_LMCE_BITS));
> > +
> Also, why do we need to look at MCG_SER_P for LMCE?

Good point. Its required by architecture, since it depends on recovery support
in processors to work. I forgot to add that to the SDM when i made those
updates. I will update the SDM appropriately on my next attempt at it.

>
> Btw, we do that already in __mcheck_cpu_cap_init() so you could check
> mca_cfg.ser here instead.

Could have used mca_cfg. But just being paranoid, would be safe to test per-cpu
instead of taking the global based on BSP. Just in case someone put
a system with slightly different capabilities.

>
>
> ECO tip #101: Trim your mails when you reply.

Sorry about my config challenges.. hopefully this makes it out with
all the responses :-)

Cheers,
Ashok




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