Re: [PATCH v4 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS

[Peter Zijlstra <peterz@infradead.org>]

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.

>  		state->enter = intel_idle_ibrs;
>  		return;
>  	}