linux-kernel - Re: new text patching for review

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Message-ID: <46A00CC2.6010407@vmware.com>
Date:	Thu, 19 Jul 2007 18:15:46 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	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

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.

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.  I didn't imagine that would be very popular, and VMI was 
the only paravirt-ops that were considering module load time patching, 
so I flushed it.

You get some other nasty issues as well with run-time switching, like 
missing early init calls (in particular, we would have to go to some 
heroics to retake the land surrounding the APIC local timer interrupt).

Zach
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