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Diffstat (limited to 'Documentation/admin-guide/pm/intel_idle.rst')
| -rw-r--r-- | Documentation/admin-guide/pm/intel_idle.rst | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst index b799a43da62e..39bd6ecce7de 100644 --- a/Documentation/admin-guide/pm/intel_idle.rst +++ b/Documentation/admin-guide/pm/intel_idle.rst @@ -170,7 +170,7 @@ and ``idle=nomwait``. If any of them is present in the kernel command line, the ``MWAIT`` instruction is not allowed to be used, so the initialization of ``intel_idle`` will fail. -Apart from that there are four module parameters recognized by ``intel_idle`` +Apart from that there are five module parameters recognized by ``intel_idle`` itself that can be set via the kernel command line (they cannot be updated via sysfs, so that is the only way to change their values). @@ -216,6 +216,21 @@ are ignored). The idle states disabled this way can be enabled (on a per-CPU basis) from user space via ``sysfs``. +The ``ibrs_off`` module parameter is a boolean flag (defaults to +false). If set, it is used to control if IBRS (Indirect Branch Restricted +Speculation) should be turned off when the CPU enters an idle state. +This flag does not affect CPUs that use Enhanced IBRS which can remain +on with little performance impact. + +For some CPUs, IBRS will be selected as mitigation for Spectre v2 and Retbleed +security vulnerabilities by default. Leaving the IBRS mode on while idling may +have a performance impact on its sibling CPU. The IBRS mode will be turned off +by default when the CPU enters into a deep idle state, but not in some +shallower ones. Setting the ``ibrs_off`` module parameter will force the IBRS +mode to off when the CPU is in any one of the available idle states. This may +help performance of a sibling CPU at the expense of a slightly higher wakeup +latency for the idle CPU. + .. _intel-idle-core-and-package-idle-states: |