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    SubjectRe: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override
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    On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:
    > The DEXCR Speculative Branch Hint Enable (SBHE) aspect controls whether
    > the hints provided by BO field of Branch instructions are obeyed during
    > speculative execution.
    >
    > SBHE behaviour per ISA 3.1B:
    >
    > 0: The hints provided by BO field of Branch instructions may be
    > ignored during speculative execution
    >
    > 1: The hints provided by BO field of Branch instructions are obeyed
    > during speculative execution
    >
    > Add a sysctl entry to allow changing this aspect globally in the system
    > at runtime:
    >
    > /proc/sys/kernel/speculative_branch_hint_enable
    >
    > Three values are supported:
    >
    > -1: Disable DEXCR SBHE sysctl override
    > 0: Override and set DEXCR[SBHE] aspect to 0
    > 1: Override and set DEXCR[SBHE] aspect to 1
    >
    > Internally, introduces a mechanism to apply arbitrary system wide
    > overrides on top of the prctl() config.

    Why have an override for this, and not others?

    Thanks,
    Nick

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