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    SubjectRe: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok
    On Sun, Jan 7, 2018 at 11:47 AM, Linus Torvalds
    <torvalds@linux-foundation.org> wrote:
    > On Sat, Jan 6, 2018 at 10:33 PM, Willy Tarreau <w@1wt.eu> wrote:
    >>
    >> To be fair there's overreaction on both sides. The vast majority of
    >> users need to get a 100% safe system and will never notice any
    >> difference.
    >
    > There is no such thing as a "100% safe system". Never will be - unless
    > you make sure you have no users.
    >
    > Also, people definitely *are* noticing the performance issues with the
    > current set of patches, and they are causing real problems. Go search
    > for reports of Amazon AWS slowdowns.
    >
    > So this whole "security is so important that performance doesn't
    > matter" mindset is pure and utter garbage.
    >
    > And the whole "normal people won't even notice" is pure garbage too.
    > Don't spread that bullshit when you see actual normal people
    > complaining.
    >
    > Performance matters. A *LOT*.

    I'm thinking we should provide the option to at least build the
    hot-path nospec_array_ptr() usages without an lfence.

    CONFIG_SPECTRE1_PARANOIA_SAFE
    CONFIG_SPECTRE1_PARANOIA_PERF

    ...if only for easing performance testing and let the distribution set
    its policy.

    Where hot-path usages can do:

    nospec_relax(nospec_array_ptr())

    ...to optionally ellide the lfence.

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