Re: [PATCH v8 13/18] vfio/platform: support for maskable and automasked interrupts

[Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Mon, 2014-10-13 at 15:10 +0200, Antonios Motakis wrote:
> Adds support to mask interrupts, and also for automasked interrupts.
> Level sensitive interrupts are exposed as automasked interrupts and
> are masked and disabled automatically when they fire.
> 
> Signed-off-by: Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>
> ---
>  drivers/vfio/platform/vfio_platform_irq.c     | 94 +++++++++++++++++++++++++--
>  drivers/vfio/platform/vfio_platform_private.h |  2 +
>  2 files changed, 91 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform_irq.c b/drivers/vfio/platform/vfio_platform_irq.c
> index 4359b9c..7620a17 100644
> --- a/drivers/vfio/platform/vfio_platform_irq.c
> +++ b/drivers/vfio/platform/vfio_platform_irq.c
> @@ -31,27 +31,103 @@
>  
>  #include "vfio_platform_private.h"
>  
> +static void vfio_platform_mask(struct vfio_platform_irq *irq_ctx)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&irq_ctx->lock, flags);
> +
> +	if (!irq_ctx->masked) {
> +		disable_irq(irq_ctx->hwirq);
> +		irq_ctx->masked = true;
> +	}
> +
> +	spin_unlock_irqrestore(&irq_ctx->lock, flags);
> +}
> +
>  static int vfio_platform_set_irq_mask(struct vfio_platform_device *vdev,
>  				    unsigned index, unsigned start,
>  				    unsigned count, uint32_t flags, void *data)
>  {
> -	return -EINVAL;
> +	if (start != 0 || count != 1)
> +		return -EINVAL;
> +
> +	if (flags & VFIO_IRQ_SET_DATA_EVENTFD)
> +		return -EINVAL; /* not implemented yet */
> +
> +	if (flags & VFIO_IRQ_SET_DATA_NONE) {
> +		vfio_platform_mask(&vdev->irqs[index]);
> +
> +	} else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
> +		uint8_t mask = *(uint8_t *)data;
> +
> +		if (mask)
> +			vfio_platform_mask(&vdev->irqs[index]);
> +	}
> +
> +	return 0;
> +}
> +
> +static void vfio_platform_unmask(struct vfio_platform_irq *irq_ctx)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&irq_ctx->lock, flags);
> +
> +	if (irq_ctx->masked) {
> +		enable_irq(irq_ctx->hwirq);
> +		irq_ctx->masked = false;
> +	}
> +
> +	spin_unlock_irqrestore(&irq_ctx->lock, flags);
>  }
>  
>  static int vfio_platform_set_irq_unmask(struct vfio_platform_device *vdev,
>  				    unsigned index, unsigned start,
>  				    unsigned count, uint32_t flags, void *data)
>  {
> -	return -EINVAL;
> +	if (start != 0 || count != 1)
> +		return -EINVAL;
> +
> +	if (flags & VFIO_IRQ_SET_DATA_EVENTFD)
> +		return -EINVAL; /* not implemented yet */
> +
> +	if (flags & VFIO_IRQ_SET_DATA_NONE) {
> +		vfio_platform_unmask(&vdev->irqs[index]);
> +
> +	} else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
> +		uint8_t unmask = *(uint8_t *)data;
> +
> +		if (unmask)
> +			vfio_platform_unmask(&vdev->irqs[index]);
> +	}
> +
> +	return 0;
>  }
>  
>  static irqreturn_t vfio_irq_handler(int irq, void *dev_id)
>  {
>  	struct vfio_platform_irq *irq_ctx = dev_id;
> +	unsigned long flags;
> +	int ret = IRQ_NONE;
>  
> -	eventfd_signal(irq_ctx->trigger, 1);
> +	spin_lock_irqsave(&irq_ctx->lock, flags);
> +
> +	if (!irq_ctx->masked) {
> +		ret = IRQ_HANDLED;
> +
> +		if (irq_ctx->flags & VFIO_IRQ_INFO_AUTOMASKED) {
> +			disable_irq_nosync(irq_ctx->hwirq);
> +			irq_ctx->masked = true;
> +		}
> +	}
>  
> -	return IRQ_HANDLED;
> +	spin_unlock_irqrestore(&irq_ctx->lock, flags);
> +
> +	if (ret == IRQ_HANDLED)
> +		eventfd_signal(irq_ctx->trigger, 1);
> +
> +	return ret;
>  }

If you actually have edge interrupts, you're unnecessarily penalizing
them with the spinlock here.  You could do like vfio-pci and only
advertise level interrupts as maskable then use separate edge vs level
handlers.

>  
>  static int vfio_set_trigger(struct vfio_platform_device *vdev,
> @@ -169,9 +245,17 @@ int vfio_platform_irq_init(struct vfio_platform_device *vdev)
>  		if (hwirq < 0)
>  			goto err;
>  
> -		vdev->irqs[i].flags = VFIO_IRQ_INFO_EVENTFD;
> +		spin_lock_init(&vdev->irqs[i].lock);
> +
> +		vdev->irqs[i].flags = VFIO_IRQ_INFO_EVENTFD
> +					| VFIO_IRQ_INFO_MASKABLE;
> +
> +		if (irq_get_trigger_type(hwirq) & IRQ_TYPE_LEVEL_MASK)
> +			vdev->irqs[i].flags |= VFIO_IRQ_INFO_AUTOMASKED;
> +
>  		vdev->irqs[i].count = 1;
>  		vdev->irqs[i].hwirq = hwirq;
> +		vdev->irqs[i].masked = false;
>  	}
>  
>  	vdev->num_irqs = cnt;
> diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
> index 47af6e0..65e80e7 100644
> --- a/drivers/vfio/platform/vfio_platform_private.h
> +++ b/drivers/vfio/platform/vfio_platform_private.h
> @@ -30,6 +30,8 @@ struct vfio_platform_irq {
>  	int			hwirq;
>  	char			*name;
>  	struct eventfd_ctx	*trigger;
> +	bool			masked;
> +	spinlock_t		lock;
>  };
>  
>  struct vfio_platform_region {