linux-kernel - Re: new text patching for review

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Message-ID: <20070720073726.GB19833@one.firstfloor.org>
Date:	Fri, 20 Jul 2007 09:37:26 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Zachary Amsden <zach@...are.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Andi Kleen <andi@...stfloor.org>, jbeulich@...ell.com,
	"S. P. Prasanna" <prasanna@...ibm.com>,
	linux-kernel@...r.kernel.org, patches@...-64.org,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: new text patching for review

On Thu, Jul 19, 2007 at 06:15:46PM -0700, Zachary Amsden wrote:
> Mathieu Desnoyers wrote:
> >Yes, kprobes is case 1: atomic update. And we don't even have to bother
> >about Intel's erratum. This one is ok. That's mainly the
> >alternatives/paravirt code I worry about.
> >  
> 
> Paravirt and alternatives should all be ok because they are done before 
> SMP bringup and with NMIs disabled.  NMI watchdog is not setup until 
> smp_prepare_cpus/check_nmi_watchdog, which happens way later, not during 
> parse_args/setup_nmi_watchdog, which just decides which type of watchdog 
> to setup.

There could be other NMIs too - e.g. caused by IO devices or NMI
buttons - but they're relatively unlikely.

> 
> I originally considered the NMI problem for paravirt-ops patching done 
> during module load, and found that I would need to modify 
> stop_machine_run to have an architecture specific callout to mask and 
> unmask NMIs.

When your virtual machine never injects NMIs or MCEs you're ok.

-Andi
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