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    SubjectRe: [patch V4 part 1 35/36] x86: Replace ist_enter() with nmi_enter()
    On Thu, May 07, 2020 at 02:17:58PM -0400, Mathieu Desnoyers wrote:
    > ----- On May 7, 2020, at 2:04 PM, Andy Lutomirski luto@kernel.org wrote:
    >
    > > On Tue, May 5, 2020 at 7:14 AM Thomas Gleixner <tglx@linutronix.de> wrote:
    > >>
    > >> From: Peter Zijlstra <peterz@infradead.org>
    > >>
    > >> A few exceptions (like #DB and #BP) can happen at any location in the code,
    > >> this then means that tracers should treat events from these exceptions as
    > >> NMI-like. The interrupted context could be holding locks with interrupts
    > >> disabled for instance.
    > >>
    > >> Similarly, #MC is an actual NMI-like exception.
    > >
    > > Is it permissible to send a signal from inside nmi_enter()? I imagine
    > > so, but I just want to make sure.
    >
    > If you mean sending a proper signal, I would guess not.
    >
    > I suspect you'll rather want to use "irq_work()" from NMI context to ensure
    > the rest of the work (e.g. sending a signal or a wakeup) is performed from
    > IRQ context very soon after the NMI, rather than from NMI context.
    >
    > AFAIK this is how this is done today by perf, ftrace, ebpf, and lttng.

    What Mathieu says. But I suspect you want to keep reading until
    part4-18. That should get you what you really want.

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