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    SubjectRe: config SCHED_CORE
    On Fri, May 21, 2021 at 3:53 AM Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > On Thu, May 20, 2021 at 08:06:07PM -0700, Hugh Dickins wrote:
    > > Hi Peter,
    > >
    > > make oldconfig gave me no help at all on how to decide whether to choose
    > > SCHED_CORE Y or n, beyond it recommending Y. Maybe you'll delete that
    > > option later, or maybe removing the prompt string would silence it.
    >
    > Ah, you're quite right. I never seem to have gotten around to actually
    > writing anything useful there :/ Similarly the documentation for all
    > this seems to have gone missing too.
    >
    > Joel, could I ask you to refresh the document to match the current state
    > of things and repost? I still whole hartedly despise this RST crud, it
    > makes it so hard to read / modify the files.
    >
    > ( I think the latest version is here:
    > https://lkml.kernel.org/r/20210324214020.34142-8-joel@joelfernandes.org
    > )
    >
    > Anyway, how is something like the below, Joel can add a reference to the
    > document once it's there.

    Sure thing, Peter! I will work on it and post a patch.

    - Joel


    >
    > ---
    > kernel/Kconfig.preempt | 14 +++++++++++++-
    > 1 file changed, 13 insertions(+), 1 deletion(-)
    >
    > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
    > index ea1e3331c0ba..3c4566cd20ef 100644
    > --- a/kernel/Kconfig.preempt
    > +++ b/kernel/Kconfig.preempt
    > @@ -104,4 +104,16 @@ config SCHED_CORE
    > bool "Core Scheduling for SMT"
    > default y
    > depends on SCHED_SMT
    > -
    > + help
    > + This option enables Core scheduling, a means of coordinated task
    > + selection across SMT siblings with the express purpose of creating a
    > + Core wide privilidge boundary. When enabled -- see prctl(PR_SCHED_CORE)
    > + -- task selection will ensure all SMT siblings will execute a task
    > + from the same 'core group', forcing idle when no matching task is found.
    > +
    > + This provides means of mitigation against a number of SMT side-channels;
    > + but is, on its own, insufficient to mitigate all known side-channels.
    > + Notable: the MDS class of attacks require more.
    > +
    > + Default enabled for anything that has SCHED_SMT, when unused there should
    > + be no impact on performance.

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