Re: new text patching for review

[Zachary Amsden <zach@vmware.com>]

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