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    SubjectRe: Dealing with the NMI mess
    On Fri, Jul 24, 2015 at 11:29:29AM -0700, Linus Torvalds wrote:
    > On Fri, Jul 24, 2015 at 8:30 AM, Peter Zijlstra <peterz@infradead.org> wrote:
    > > On Fri, Jul 24, 2015 at 05:26:37PM +0200, Willy Tarreau wrote:
    > >> >
    > >> > The point is, if we trigger a #DB on an instruction breakpoint
    > >> > while !IF, then we simply disable that breakpoint and do the RET.
    > >>
    > >> Yes but the breakpoint remains disabled then. Or I'm missing
    > >> something.
    > >
    > > http://marc.info/?l=linux-kernel&m=143773601130974
    > >
    > > We re-enable before going back to userspace.
    >
    > Actually, Andy had a good argument that we don't even need this.
    >
    > We just don't ever need to disable data breakpoints. Even if we end up doing
    >
    > cli();
    > copy_from_user_inatomic();
    >
    > that actually works fine. If there are data breakpoints, we will have

    I worry that we'll end up running the do_debug() handlers from effective
    NMI context.

    The NMI might have preempted locks which these handlers require etc..


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