Re: [PATCH v9 12/19] vfio/platform: trigger an interrupt via eventfd

[Antonios Motakis]

On Wed, Nov 12, 2014 at 3:22 PM, Eric Auger <eric.auger@xxxxxxxxxx> wrote:
> On 10/31/2014 08:36 PM, Alex Williamson wrote:
>> On Mon, 2014-10-27 at 19:07 +0100, Antonios Motakis wrote:
>>> This patch allows to set an eventfd for a patform device's interrupt,
> platform device (typo)

Ack.

>>> and also to trigger the interrupt eventfd from userspace for testing.
>>> Level sensitive interrupts are marked as maskable and are handled in
>>> a later patch. Edge triggered interrupts are not advertised as maskable
>>> and are implemented here using a simple and efficient IRQ handler.
>>>
>>> Signed-off-by: Antonios Motakis <a.motakis@xxxxxxxxxxxxxxxxxxxxxx>
>>> ---
>>>  drivers/vfio/platform/vfio_platform_irq.c     | 93 ++++++++++++++++++++++++++-
>>>  drivers/vfio/platform/vfio_platform_private.h |  2 +
>>>  2 files changed, 93 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/vfio/platform/vfio_platform_irq.c b/drivers/vfio/platform/vfio_platform_irq.c
>>> index 007b386..2ac8ed7 100644
>>> --- a/drivers/vfio/platform/vfio_platform_irq.c
>>> +++ b/drivers/vfio/platform/vfio_platform_irq.c
>>> @@ -45,11 +45,91 @@ static int vfio_platform_set_irq_unmask(struct vfio_platform_device *vdev,
>>>      return -EINVAL;
>>>  }
>>>
>>> +static irqreturn_t vfio_irq_handler(int irq, void *dev_id)
>>> +{
>>> +    struct vfio_platform_irq *irq_ctx = dev_id;
>>> +
>>> +    eventfd_signal(irq_ctx->trigger, 1);
>>> +
>>> +    return IRQ_HANDLED;
>>> +}
>>> +
>>> +static int vfio_set_trigger(struct vfio_platform_device *vdev, int index,
>>> +                        int fd, irq_handler_t handler)
>>> +{
>>> +    struct vfio_platform_irq *irq = &vdev->irqs[index];
>>> +    struct eventfd_ctx *trigger;
>>> +    int ret;
>>> +
>>> +    if (irq->trigger) {
>>> +            free_irq(irq->hwirq, irq);
>>> +            kfree(irq->name);
>>> +            eventfd_ctx_put(irq->trigger);
>>> +            irq->trigger = NULL;
>>> +    }
>>> +
>>> +    if (fd < 0) /* Disable only */
>>> +            return 0;
>>> +
>>> +    irq->name = kasprintf(GFP_KERNEL, "vfio-irq[%d](%s)",
>>> +                                            irq->hwirq, vdev->name);
>>> +    if (!irq->name)
>>> +            return -ENOMEM;
>>> +
>>> +    trigger = eventfd_ctx_fdget(fd);
>>> +    if (IS_ERR(trigger)) {
>>> +            kfree(irq->name);
>>> +            return PTR_ERR(trigger);
>>> +    }
>>> +
>>> +    irq->trigger = trigger;
>>> +
>>> +    ret = request_irq(irq->hwirq, handler, 0, irq->name, irq);
>>> +    if (ret) {
>>> +            kfree(irq->name);
>>> +            eventfd_ctx_put(trigger);
>>> +            irq->trigger = NULL;
>>> +            return ret;
>>> +    }
>>> +
>>> +    return 0;
> you may simply return ret here?

Indeed, ack.

>>> +}
>>> +
>>>  static int vfio_platform_set_irq_trigger(struct vfio_platform_device *vdev,
>>>                                   unsigned index, unsigned start,
>>>                                   unsigned count, uint32_t flags, void *data)
>>>  {
>>> -    return -EINVAL;
>>> +    struct vfio_platform_irq *irq = &vdev->irqs[index];
>>> +    irq_handler_t handler;
>>> +
>>> +    if (vdev->irqs[index].flags & VFIO_IRQ_INFO_MASKABLE)
>>> +            return -EINVAL; /* not implemented */
>>> +    else
>>> +            handler = vfio_irq_handler;
>>> +
>>> +    if (!count && (flags & VFIO_IRQ_SET_DATA_NONE))
>>> +            return vfio_set_trigger(vdev, index, -1, handler);
>>> +
>>> +    if (start != 0 || count != 1)
>>> +            return -EINVAL;
>>> +
>>> +    if (flags & VFIO_IRQ_SET_DATA_EVENTFD) {
>>> +            int32_t fd = *(int32_t *)data;
>>> +
>>> +            return vfio_set_trigger(vdev, index, fd, handler);
>>> +    }
>>> +
>>> +    if (flags & VFIO_IRQ_SET_DATA_NONE) {
>>> +            handler(irq->hwirq, irq);
>>> +
>>> +    } else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
>>> +            uint8_t trigger = *(uint8_t *)data;
>>> +
>>> +            if (trigger)
>>> +                    handler(irq->hwirq, irq);
>>> +    }
>>> +
>>> +    return 0;
>>>  }
>>>
>>>  int vfio_platform_set_irqs_ioctl(struct vfio_platform_device *vdev,
>>> @@ -95,7 +175,11 @@ int vfio_platform_irq_init(struct vfio_platform_device *vdev)
>>>              if (hwirq < 0)
>>>                      goto err;
>>>
>>> -            vdev->irqs[i].flags = 0;
>>> +            vdev->irqs[i].flags = VFIO_IRQ_INFO_EVENTFD;
>>> +
>>> +            if (irq_get_trigger_type(hwirq) & IRQ_TYPE_LEVEL_MASK)
>>> +                    vdev->irqs[i].flags |= VFIO_IRQ_INFO_MASKABLE;
>>
>> This is a bit confusing because edge interrupts can support masking, but
>> they don't require it.  Level interrupts really must support masking
>> because we need to mask them on the host and therefore the user needs to
>> be able to unmask them (ignoring the irq prioritization thing you guys
>> can do on arm).  So this works, but I would really have expected
>> VFIO_IRQ_INFO_AUTOMASKED here and in the above function.
>
> Shouldn't we have AUTOMASKED for level sensitive and MASKABLE for both
> level & edge?

I believe it was Alex's argument to expose edge triggered irqs as
non-MASKABLE so they can benefit from a more efficient interrupt
handler.

Would it be acceptable to make them both maskable, but check for
masked status without a lock?

>
> For forwarded IRQ, may I enrich the external API with a new function
> enabling to turn the automasked flag off? Would that make sense?

Are you thinking of an external function but internal to the kernel,
or the external user API?

>
> Thanks
>
> Eric
>>
>>> +
>>>              vdev->irqs[i].count = 1;
>>>              vdev->irqs[i].hwirq = hwirq;
>>>      }
>>> @@ -110,6 +194,11 @@ err:
>>>
>>>  void vfio_platform_irq_cleanup(struct vfio_platform_device *vdev)
>>>  {
>>> +    int i;
>>> +
>>> +    for (i = 0; i < vdev->num_irqs; i++)
>>> +            vfio_set_trigger(vdev, i, -1, NULL);
>>> +
>>>      vdev->num_irqs = 0;
>>>      kfree(vdev->irqs);
>>>  }
>>> diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
>>> index ffa2459..a3f2411 100644
>>> --- a/drivers/vfio/platform/vfio_platform_private.h
>>> +++ b/drivers/vfio/platform/vfio_platform_private.h
>>> @@ -28,6 +28,8 @@ struct vfio_platform_irq {
>>>      u32                     flags;
>>>      u32                     count;
>>>      int                     hwirq;
>>> +    char                    *name;
>>> +    struct eventfd_ctx      *trigger;
>>>  };
>>>
>>>  struct vfio_platform_region {
>>
>>
>>
>
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