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SubjectRe: 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).

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