Re: [PATCH v3 06/10] VFIO: platform: add irq bypass producer management

[Alex Williamson]

On Mon, 2015-08-10 at 15:21 +0200, Eric Auger wrote:
> This patch populates the IRQ bypass callacks:
> - stop/start producer simply consist in disabling/enabling the host irq
> - add/del consumer: basically set the automasked flag to false/true
> 
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> 
> ---
> v2 -> v3:
> - vfio_platform_irq_bypass_add_consumer now returns an error in case
>   the IRQ is recognized as active
> - active boolean not set anymore
> - do not VFIO mask the IRQ anymore on unforward
> 
> v1 -> v2:
> - device handle caching in vfio_platform_device is introduced in a
>   separate patch
> - use container_of
> ---
>  drivers/vfio/platform/vfio_platform_irq.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_irq.c b/drivers/vfio/platform/vfio_platform_irq.c
> index efaee58..400a188 100644
> --- a/drivers/vfio/platform/vfio_platform_irq.c
> +++ b/drivers/vfio/platform/vfio_platform_irq.c
> @@ -224,23 +224,44 @@ static int vfio_platform_is_active(struct vfio_platform_irq *irq)
>  
>  static void vfio_platform_irq_bypass_stop(struct irq_bypass_producer *prod)
>  {
> +	disable_irq(prod->irq);
>  }
>  
>  static void vfio_platform_irq_bypass_start(struct irq_bypass_producer *prod)
>  {
> +	enable_irq(prod->irq);
>  }
>  
>  static int vfio_platform_irq_bypass_add_consumer(
>  			struct irq_bypass_producer *prod,
>  			struct irq_bypass_consumer *cons)
>  {
> -	return 0;
> +	struct vfio_platform_irq *irq =
> +		container_of(prod, struct vfio_platform_irq, producer);
> +
> +	/*
> +	 * if the IRQ is active at irqchip level or VFIO (auto)masked
> +	 * this means the host IRQ is already under injection in the
> +	 * guest and this not safe to change the forwarding state at
> +	 * that stage.
> +	 * It is not possible to differentiate user-space masking
> +	 * from auto-masking, leading to possible false detection of
> +	 * active state.
> +	 */
> +	if (vfio_platform_is_active(irq))
> +		return -EAGAIN;

Here's an example of why we don't want WARN_ON if a registration fails,
this is effectively random.  When and how is a re-try going to happen?

> +
> +	return vfio_platform_set_automasked(irq, false);

set_forwarded just seems so much more logical here.

>  }
>  
>  static void vfio_platform_irq_bypass_del_consumer(
>  			struct irq_bypass_producer *prod,
>  			struct irq_bypass_consumer *cons)
>  {
> +	struct vfio_platform_irq *irq =
> +		container_of(prod, struct vfio_platform_irq, producer);
> +
> +	vfio_platform_set_automasked(irq, true);
>  }
>  
>  static int vfio_set_trigger(struct vfio_platform_device *vdev, int index,



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