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    SubjectRe: [patch 2/2] x86 NMI-safe INT3 and Page Fault
    On 07/16/2010 10:54 AM, Avi Kivity wrote:
    > On 07/16/2010 07:58 PM, Mathieu Desnoyers wrote:
    >>> Why is that kernel code calling vmalloc_sync_all()? If it is only NMI
    >>> which cannot take vmalloc faults, why bother? If not, why not?
    >> Modules come as yet another example of stuff that is loaded in vmalloc'd space
    >> and can be accesses from NMI context. That would include oprofile, tracers, and
    >> probably others I'm forgetting about.
    > Module loading can certainly take a vmalloc_sync_all() (though I agree
    > it's unpleasant). Anything else?
    > Note perf is not modular at this time, but could be made so with
    > preempt/sched notifiers to hook the context switch.

    Actually, module loading is already a performance problem; a lot of
    distros load sometimes hundreds of modules on startup, and it's heavily
    serialized, so I can see this being desirable to skip.

    I really hope noone ever gets the idea of touching user space from an
    NMI handler, though, and expecting it to work...


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