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    SubjectRe: [patch 2/2] x86 NMI-safe INT3 and Page Fault
    On 08/04/2010 02:46 AM, Peter Zijlstra wrote:
    > On Fri, 2010-07-16 at 11:05 -0700, H. Peter Anvin wrote:
    >>
    >> I really hope noone ever gets the idea of touching user space from an
    >> NMI handler, though, and expecting it to work...
    >
    > Perf actually already does that to unwind user-space stacks... ;-)
    >
    > See arch/x86/kernel/cpu/perf_event.c:copy_from_user_nmi() and its users.
    >
    > What we do is a manual page table walk (using __get_user_pages_fast) and
    > simply bail when the page is not available.
    >

    That's not really "touching user space", though.

    -hpa


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