linux-kernel - Re: [PATCH v3] x86/mce: Honour bios-set CMCI threshold

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Date:	Wed, 17 Oct 2012 15:09:34 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:	tony.luck@...el.com, gong.chen@...ux.intel.com, ananth@...ibm.com,
	masbock@...ux.vnet.ibm.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, bp@...64.org, lcm@...ibm.com,
	andi@...stfloor.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, gregkh@...e.de, linux-edac@...r.kernel.org
Subject: Re: [PATCH v3] x86/mce: Honour bios-set CMCI threshold

On Wed, Oct 17, 2012 at 04:57:30PM +0530, Naveen N. Rao wrote:
> On 10/17/2012 04:29 PM, Borislav Petkov wrote:
> >>>
> >>>+static struct dev_ext_attribute dev_attr_bios_cmci_threshold = {
> >>>+	__ATTR(bios_cmci_threshold, 0444, device_show_int, NULL),
> >>>+	&mce_bios_cmci_threshold
> >
> >Ok, I just noticed this (we must've missed it during review) but why is
> >this read-only? If it has to be read-only, why do we have a node for
> >this in sysfs instead of simply issuing the printk statements below and
> >people who are interested in this, can grep dmesg?
> 
> This was added so that user-space tools could find out if we're
> using thresholds for CMCI.

That I figured out.

What I can't figure out is why userspace tools need to know that - the
fact that some MCI_CTL2 has a 0 CMCI threshold because BIOS forgot to
set it correctly? IOW, this is a rather evolved workaround for b0rked
BIOS (the gazillionth BIOS f*ckup, btw if someone is counting :)) and,
on top of that, we have a read-only, special sysfs node which is pretty
useless to me.

Why?

-- 
Regards/Gruss,
Boris.
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