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    SubjectRe: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation
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    > On May 14, 2020, at 6:15 AM, Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > On Thu, May 14, 2020 at 02:51:32PM +0200, Thomas Gleixner wrote:
    >> Peter Zijlstra <peterz@infradead.org> writes:
    >>> On Wed, May 13, 2020 at 09:57:52PM -0700, Andy Lutomirski wrote:
    >>>>> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@linutronix.de> wrote:
    >>>>>>
    >>>>>> From: Peter Zijlstra <peterz@infradead.org>
    >>>>>>
    >>>>>> Use arch_atomic_*() and READ_ONCE_NOCHECK() to ensure nothing untoward
    >>>>>> creeps in and ruins things.
    >>>>>>
    >>>>>> That is; this is the INT3 text poke handler, strictly limit the code
    >>>>>> that runs in it, lest it inadvertenly hits yet another INT3.
    >>>>>
    >>>>>
    >>>>> Acked-by: Andy Lutomirski <luto@kernel.org>
    >>>>>
    >>>>> Does objtool catch this error?
    >>>
    >>> It does not. I'll put it on the (endless) todo list..
    >>
    >> Well, at least it detects when that code calls out into something which
    >> is not in the non-instrumentable section.
    >
    > True, but the more specific problem is that noinstr code can use
    > jump_label/static_call just fine.
    >
    > So a more specific test is validating none of that happens in the INT3
    > handler before poke_int3_handler(). Which is what I think Andy was
    > after.

    Exactly. I admit that sleep-deprived Andy was actually thinking “tglx and/or PeterZ found this by inspection, and somewhere it escaped objtool’s notice,” which is sort of the same thing :)
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