linux-kernel - Re: [Patch V1 2/3] x86, mce: Add infrastructure required to support LMCE

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Date:	Mon, 1 Jun 2015 11:48:57 -0700
From:	"Raj, Ashok" <ashok.raj@...el.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>,
	Ashok Raj <ashok.raj@...el.com>
Subject: Re: [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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