linux-kernel - Re: [PATCH v3 03/10] VFIO: platform: single handler using function pointer

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Date:	Mon, 17 Aug 2015 17:25:52 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	eric.auger@...com, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
	christoffer.dall@...aro.org, marc.zyngier@....com,
	feng.wu@...el.com, linux-kernel@...r.kernel.org,
	patches@...aro.org, pbonzini@...hat.com
Subject: Re: [PATCH v3 03/10] VFIO: platform: single handler using function
 pointer

Alex,
On 08/12/2015 08:56 PM, Alex Williamson wrote:
> On Mon, 2015-08-10 at 15:20 +0200, Eric Auger wrote:
>> A single handler now is registered whatever the use case: automasked
>> or not. A function pointer is set according to the wished behavior
>> and the handler calls this function.
>>
>> The irq lock is taken/released in the root handler. eventfd_signal can
>> be called in regions not allowed to sleep.
>>
>> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>>
>> ---
>>
>> v4: creation
>> ---
>>  drivers/vfio/platform/vfio_platform_irq.c     | 21 +++++++++++++++------
>>  drivers/vfio/platform/vfio_platform_private.h |  1 +
>>  2 files changed, 16 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/vfio/platform/vfio_platform_irq.c b/drivers/vfio/platform/vfio_platform_irq.c
>> index 40f057a..b31b1f0 100644
>> --- a/drivers/vfio/platform/vfio_platform_irq.c
>> +++ b/drivers/vfio/platform/vfio_platform_irq.c
>> @@ -148,11 +148,8 @@ static int vfio_platform_set_irq_unmask(struct vfio_platform_device *vdev,
>>  static irqreturn_t vfio_automasked_irq_handler(int irq, void *dev_id)
>>  {
>>  	struct vfio_platform_irq *irq_ctx = dev_id;
>> -	unsigned long flags;
>>  	int ret = IRQ_NONE;
>>  
>> -	spin_lock_irqsave(&irq_ctx->lock, flags);
>> -
>>  	if (!irq_ctx->masked) {
>>  		ret = IRQ_HANDLED;
>>  
>> @@ -161,8 +158,6 @@ static irqreturn_t vfio_automasked_irq_handler(int irq, void *dev_id)
>>  		irq_ctx->masked = true;
>>  	}
>>  
>> -	spin_unlock_irqrestore(&irq_ctx->lock, flags);
>> -
>>  	if (ret == IRQ_HANDLED)
>>  		eventfd_signal(irq_ctx->trigger, 1);
> 
> Has this been run with lockdep to check whether this is safe to call
> with spinlock_irqsave held?

No I did not check with lockdep and I will do. There is a comment in
fs/eventfd.c in eventfd_signal function comments that says:

"This function is supposed to be called by the kernel in paths that do
not allow sleeping. In this function we allow the counter to reach the
ULLONG_MAX value, and we signal this as overflow condition by returining
a POLLERR to poll(2)."

so I understood from this it is safe.

Best Regards

Eric

> 
>>  
>> @@ -178,6 +173,19 @@ static irqreturn_t vfio_irq_handler(int irq, void *dev_id)
>>  	return IRQ_HANDLED;
>>  }
>>  
>> +static irqreturn_t vfio_handler(int irq, void *dev_id)
>> +{
>> +	struct vfio_platform_irq *irq_ctx = dev_id;
>> +	unsigned long flags;
>> +	irqreturn_t ret;
>> +
>> +	spin_lock_irqsave(&irq_ctx->lock, flags);
>> +	ret = irq_ctx->handler(irq, dev_id);
>> +	spin_unlock_irqrestore(&irq_ctx->lock, flags);
>> +
>> +	return ret;
>> +}
>> +
>>  static void vfio_platform_irq_bypass_stop(struct irq_bypass_producer *prod)
>>  {
>>  }
>> @@ -229,9 +237,10 @@ static int vfio_set_trigger(struct vfio_platform_device *vdev, int index,
>>  	}
>>  
>>  	irq->trigger = trigger;
>> +	irq->handler = handler;
>>  
>>  	irq_set_status_flags(irq->hwirq, IRQ_NOAUTOEN);
>> -	ret = request_irq(irq->hwirq, handler, 0, irq->name, irq);
>> +	ret = request_irq(irq->hwirq, vfio_handler, 0, irq->name, irq);
>>  	if (ret) {
>>  		kfree(irq->name);
>>  		eventfd_ctx_put(trigger);
>> diff --git a/drivers/vfio/platform/vfio_platform_private.h b/drivers/vfio/platform/vfio_platform_private.h
>> index 8b4f814..f848a6b 100644
>> --- a/drivers/vfio/platform/vfio_platform_private.h
>> +++ b/drivers/vfio/platform/vfio_platform_private.h
>> @@ -40,6 +40,7 @@ struct vfio_platform_irq {
>>  	struct virqfd		*mask;
>>  	struct irq_bypass_producer producer;
>>  	bool			forwarded;
>> +	irqreturn_t (*handler)(int irq, void *dev_id);
>>  };
>>  
>>  struct vfio_platform_region {
> 
> 
> 

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