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SubjectRe: [PATCH v4 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS
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On 7/3/23 06:32, Peter Zijlstra wrote:
> On Tue, Jun 27, 2023 at 10:25:54PM -0400, Waiman Long wrote:
>
>> @@ -69,6 +69,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1;
>> static unsigned int disabled_states_mask __read_mostly;
>> static unsigned int preferred_states_mask __read_mostly;
>> static bool force_irq_on __read_mostly;
>> +static bool ibrs_off __read_mostly;
>>
>> static struct cpuidle_device __percpu *intel_idle_cpuidle_devices;
>>
>> @@ -1919,12 +1920,15 @@ static void state_update_enter_method(struct cpuidle_state *state, int cstate)
>> }
>>
>> if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) &&
>> - state->flags & CPUIDLE_FLAG_IBRS) {
>> + ((state->flags & CPUIDLE_FLAG_IBRS) || ibrs_off)) {
>> /*
>> * IBRS mitigation requires that C-states are entered
>> * with interrupts disabled.
>> */
>> - WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
>> + if (ibrs_off && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE))
>> + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE;
>> + else
>> + WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
> If you're respinning this, you can leave out the else and avoid the
> indent on the WARN:
>
> + if (ibrs_off && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE))
> + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE;
> WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE);
>
> Same effect, simpler code and all that.

That is true. I can certainly respin that as there is another suggested
doc change that is pending.

Cheers,
Longman

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