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    SubjectRe: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
    On Thu, Apr 12, 2018 at 12:43 PM, Linus Torvalds
    <torvalds@linux-foundation.org> wrote:
    > On Thu, Apr 12, 2018 at 12:27 PM, Mathieu Desnoyers
    > <mathieu.desnoyers@efficios.com> wrote:
    >> The cpu_opv system call executes a vector of operations on behalf of
    >> user-space on a specific CPU with preemption disabled. It is inspired
    >> by readv() and writev() system calls which take a "struct iovec"
    >> array as argument.
    >
    > Do we really want the page pinning?
    >
    > This whole cpu_opv thing is the most questionable part of the series,
    > and the page pinning is the most questionable part of cpu_opv for me.
    >
    > Can we plan on merging just the plain rseq parts *without* this all
    > first, and then see the cpu_opv thing as a "maybe future expansion"
    > part.
    >
    > I think that would make Andy happier too.
    >

    It only makes me happier if the userspace code involved is actually
    going to work when single-stepped, which might actually be the case
    (fingers crossed). That being said, I'm not really convinced that
    cpu_opv() makes much difference here, since I'm not entirely convinced
    that user code will actually use it or that user code will actually be
    that well tested. C'est la vie.

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