Messages in this thread | | | Date | Tue, 27 Jun 2023 19:58:15 -0700 | Subject | Re: [PATCH v4 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS | From | Randy Dunlap <> |
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Hi,
On 6/27/23 19:25, Waiman Long wrote: > Documentation/admin-guide/pm/intel_idle.rst | 17 ++++++++++++++++- > drivers/idle/intel_idle.c | 14 ++++++++++++-- > 2 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst > index b799a43da62e..8604e6d1fe2c 100644 > --- a/Documentation/admin-guide/pm/intel_idle.rst > +++ b/Documentation/admin-guide/pm/intel_idle.rst
You may take or leave these comments as you choose.
> @@ -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 (default to false). It is
(default false). or (defaults to false).
Then I think it reads better if the next sentence begins with: "If set," instead of having it in the middle of the sentence.
> +used to control if IBRS (Indirect Branch Restricted Speculation) should be > +turned off, if set, when the CPU enters an idle state. This flag will not > +affect CPUs that are using 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.
thanks. -- ~Randy
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