linux-kernel - Re: [PATCH v2 4/4] irqchip: GIC: Don't deactivate interrupts forwarded to a guest

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Message-ID: <55D2EC20.9020304@linaro.org>
Date:	Tue, 18 Aug 2015 10:26:08 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
CC:	Christoffer Dall <christoffer.dall@...aro.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] irqchip: GIC: Don't deactivate interrupts forwarded
 to a guest

Hi Marc,
On 08/13/2015 10:28 AM, Marc Zyngier wrote:
> Commit 0a4377de3056 ("genirq: Introduce irq_set_vcpu_affinity() to
> target an interrupt to a VCPU") added just what we needed at the
> lowest level to allow an interrupt to be deactivated by a guest.
> 
> When such a request reaches the GIC, it knows it doesn't need to
> perform the deactivation anymore, and can safely leave the guest
> do its magic. This of course requires additional support in both
> VFIO and KVM.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/irqchip/irq-gic.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index b020c3a..ea691be 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -148,6 +148,34 @@ static inline bool primary_gic_irq(struct irq_data *d)
>  	return true;
>  }
>  
> +static inline bool cascading_gic_irq(struct irq_data *d)
> +{
> +	/*
> +	 * If handler_data pointing to one of the secondary GICs, then
> +	 * this is the cascading interrupt, and it cannot possibly be
a cascading interrupt?
> +	 * forwarded.
> +	 */
> +	if (d->handler_data >= (void *)(gic_data + 1) &&
> +	    d->handler_data <  (void *)(gic_data + MAX_GIC_NR))
there is an accessor for d->handler_data: irq_data_get_irq_handler_data

besides:
Reviewed-by: Eric Auger <eric.auger@...aro.org>
Tested-by: Eric Auger <eric.auger@...aro.org> on Calxeda Midway with
VFIO SPI assignment

Best Regards

Eric


> +		return true;
> +
> +	return false;
> +}
> +
> +static inline bool forwarded_irq(struct irq_data *d)
> +{
> +	/*
> +	 * A forwarded interrupt:
> +	 * - is on the primary GIC
> +	 * - has its handler_data set to a value
> +	 * - that isn't a secondary GIC
> +	 */
> +	if (primary_gic_irq(d) && d->handler_data && !cascading_gic_irq(d))
> +		return true;
> +
> +	return false;
> +}
> +
>  /*
>   * Routines to acknowledge, disable and enable interrupts
>   */
> @@ -166,6 +194,18 @@ static int gic_peek_irq(struct irq_data *d, u32 offset)
>  static void gic_mask_irq(struct irq_data *d)
>  {
>  	gic_poke_irq(d, GIC_DIST_ENABLE_CLEAR);
> +	/*
> +	 * When masking a forwarded interrupt, make sure it is
> +	 * deactivated as well.
> +	 *
> +	 * This ensures that an interrupt that is getting
> +	 * disabled/masked will not get "stuck", because there is
> +	 * noone to deactivate it (guest is being terminated).
> +	 */
> +	if (static_key_true(&supports_deactivate)) {
> +		if (forwarded_irq(d))
> +			gic_poke_irq(d, GIC_DIST_ACTIVE_CLEAR);
> +	}
>  }
>  
>  static void gic_unmask_irq(struct irq_data *d)
> @@ -178,6 +218,10 @@ static void gic_eoi_irq(struct irq_data *d)
>  	u32 deact_offset = GIC_CPU_EOI;
>  
>  	if (static_key_true(&supports_deactivate)) {
> +		/* Do not deactivate an IRQ forwarded to a vcpu. */
> +		if (forwarded_irq(d))
> +			return;
> +
>  		if (primary_gic_irq(d))
>  			deact_offset = GIC_CPU_DEACTIVATE;
>  	}
> @@ -251,6 +295,19 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
>  	return gic_configure_irq(gicirq, type, base, NULL);
>  }
>  
> +static int gic_irq_set_vcpu_affinity(struct irq_data *d, void *vcpu)
> +{
> +	/* Only interrupts on the primary GIC can be forwarded to a vcpu. */
> +	if (static_key_true(&supports_deactivate)) {
> +		if (primary_gic_irq(d) && !cascading_gic_irq(d)) {
> +			d->handler_data = vcpu;
> +			return 0;
> +		}
> +	}
> +
> +	return -EINVAL;
> +}
> +
>  #ifdef CONFIG_SMP
>  static int gic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
>  			    bool force)
> @@ -346,6 +403,7 @@ static struct irq_chip gic_chip = {
>  #endif
>  	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
>  	.irq_set_irqchip_state	= gic_irq_set_irqchip_state,
> +	.irq_set_vcpu_affinity	= gic_irq_set_vcpu_affinity,
>  	.flags			= IRQCHIP_SET_TYPE_MASKED,
>  };
>  
> 

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