Re: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override
From: Benjamin Gray <hidden>
Date: 2023-03-07 05:58:44
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On Tue, 2023-03-07 at 15:30 +1000, Nicholas Piggin wrote:
On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:quoted
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?
Should be in the commit message of course, but this aspect bleeds over to other processes, so a user may wish to prevent all processes from changing the value. The other aspects are probably only relevant to their own process, though the implementation here should support arbitrary system wide overrides.