linux-kernel - Re: [PATCH v13 12/22] vfio: Add notifier callback to parent's ops structure of mdev

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Date:   Wed, 16 Nov 2016 20:47:18 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     <alex.williamson@...hat.com>, <pbonzini@...hat.com>,
        <kraxel@...hat.com>, <cjia@...dia.com>, <qemu-devel@...gnu.org>,
        <kvm@...r.kernel.org>, <kevin.tian@...el.com>,
        <jike.song@...el.com>, <bjsdjshi@...ux.vnet.ibm.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 12/22] vfio: Add notifier callback to parent's ops
 structure of mdev



On 11/16/2016 12:07 PM, Dong Jia Shi wrote:
> * Kirti Wankhede <kwankhede@...dia.com> [2016-11-15 20:59:55 +0530]:
> 
> Hi Kirti,
> 
> [...]
> 
>> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c
>> index ffc36758cb84..4fc63db38829 100644
>> --- a/drivers/vfio/mdev/vfio_mdev.c
>> +++ b/drivers/vfio/mdev/vfio_mdev.c
>> @@ -24,6 +24,15 @@
>>  #define DRIVER_AUTHOR   "NVIDIA Corporation"
>>  #define DRIVER_DESC     "VFIO based driver for Mediated device"
>>
>> +static int vfio_mdev_notifier(struct notifier_block *nb, unsigned long action,
>> +			      void *data)
>> +{
>> +	struct mdev_device *mdev = container_of(nb, struct mdev_device, nb);
>> +	struct parent_device *parent = mdev->parent;
>> +
>> +	return parent->ops->notifier(mdev, action, data);
>> +}
>> +
>>  static int vfio_mdev_open(void *device_data)
>>  {
>>  	struct mdev_device *mdev = device_data;
>> @@ -36,9 +45,18 @@ static int vfio_mdev_open(void *device_data)
>>  	if (!try_module_get(THIS_MODULE))
>>  		return -ENODEV;
>>
>> +	if (likely(parent->ops->notifier)) {
>> +		mdev->nb.notifier_call = vfio_mdev_notifier;
>> +		if (vfio_register_notifier(&mdev->dev, &mdev->nb))
>> +			pr_err("Failed to register notifier for mdev\n");
> I think we should just return here if the error value is not -ENOTTY.
> 

It might be the case where iommu backend module might not support
.register_notifier(). In that case vfio_register_notifier() returns
-ENOTTY and that should not fail this open() call
Changing it to:

        ret = vfio_register_notifier(&mdev->dev, &mdev->nb);
        if (ret && (ret != -ENOTTY)) {
                pr_err("Failed to register notifier for mdev\n");
                module_put(THIS_MODULE);
                return ret;
        }

Thanks,
Kirti