linux-kernel - Re: [PATCH 22/25] x86/mcheck: Do the init in one place

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Message-ID: <20161109162451.bkch53nj32rtqszy@linutronix.de>
Date:   Wed, 9 Nov 2016 17:24:51 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Luck, Tony" <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
        rt@...utronix.de, linux-edac@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 22/25] x86/mcheck: Do the init in one place

On 2016-11-09 16:38:07 [+0100], Borislav Petkov wrote:
> On Wed, Nov 09, 2016 at 03:22:21PM +0100, Sebastian Andrzej Siewior wrote:
> > I want to get rid of non-symmetrical part and the arch hook which should
> > be part of the hp notifier itself. I wouldn't be too much afraid about
> > the when point in time when the notifier runs: It is the *first*
> > notifier that will be invoked on the target CPU. This is only a few
> > lines after the old hook. Nothing else long delaying should be invoked.
> 
> So I'm not sure *everything* mcheck_cpu_init() does should be in hotplug
> and toggle on and off. For example, we should set CR4.MCE once during
> init and that's it. Not turn it on and off. It would be pretty pointless
> IMO.
> 
> That's why the hotplug callback mce_disable_cpu() doesn't fiddle with
> CR4 - it only clears the bits in MCi_CTL. And I think we should remain
> that way.

The behaviour was not changed - it was only reorganized to keep in one
spot.

> The initial, one-time enabling of MCE features per core should be done
> only once per boot and that's it.

It is. You still want this in your hotplug code in case someone replaces
(physically) your CPU (say a larger NUMA box).

Sebastian