Re: [PATCH v0 07/15] mshv: Add ioctl support for MSHV-VFIO bridge device

[Mukesh R <mrathor@linux.microsoft.com>]

On 1/20/26 08:13, Stanislav Kinsburskii wrote:
> On Mon, Jan 19, 2026 at 10:42:22PM -0800, Mukesh R wrote:
>> From: Mukesh Rathor <mrathor@linux.microsoft.com>
>>
>> Add ioctl support for creating MSHV devices for a paritition. At
>> present only VFIO device types are supported, but more could be
>> added. At a high level, a partition ioctl to create device verifies
>> it is of type VFIO and does some setup for bridge code in mshv_vfio.c.
>> Adapted from KVM device ioctls.
>>
>> Credits: Original author: Wei Liu <wei.liu@kernel.org>
>> NB: Slightly modified from the original version.
>>
>> Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
>> ---
>>   drivers/hv/mshv_root_main.c | 126 ++++++++++++++++++++++++++++++++++++
>>   1 file changed, 126 insertions(+)
>>
>> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
>> index 83c7bad269a0..27313419828d 100644
>> --- a/drivers/hv/mshv_root_main.c
>> +++ b/drivers/hv/mshv_root_main.c
>> @@ -1551,6 +1551,129 @@ mshv_partition_ioctl_initialize(struct mshv_partition *partition)
>>   	return ret;
>>   }
>>   
>> +static long mshv_device_attr_ioctl(struct mshv_device *mshv_dev, int cmd,
>> +				   ulong uarg)
>> +{
>> +	struct mshv_device_attr attr;
>> +	const struct mshv_device_ops *devops = mshv_dev->device_ops;
>> +
>> +	if (copy_from_user(&attr, (void __user *)uarg, sizeof(attr)))
>> +		return -EFAULT;
>> +
>> +	switch (cmd) {
>> +	case MSHV_SET_DEVICE_ATTR:
>> +		if (devops->device_set_attr)
>> +			return devops->device_set_attr(mshv_dev, &attr);
>> +		break;
>> +	case MSHV_HAS_DEVICE_ATTR:
>> +		if (devops->device_has_attr)
>> +			return devops->device_has_attr(mshv_dev, &attr);
>> +		break;
>> +	}
>> +
>> +	return -EPERM;
>> +}
>> +
>> +static long mshv_device_fop_ioctl(struct file *filp, unsigned int cmd,
>> +				  ulong uarg)
>> +{
>> +	struct mshv_device *mshv_dev = filp->private_data;
>> +
>> +	switch (cmd) {
>> +	case MSHV_SET_DEVICE_ATTR:
>> +	case MSHV_HAS_DEVICE_ATTR:
>> +		return mshv_device_attr_ioctl(mshv_dev, cmd, uarg);
>> +	}
>> +
>> +	return -ENOTTY;
>> +}
>> +
>> +static int mshv_device_fop_release(struct inode *inode, struct file *filp)
>> +{
>> +	struct mshv_device *mshv_dev = filp->private_data;
>> +	struct mshv_partition *partition = mshv_dev->device_pt;
>> +
>> +	if (mshv_dev->device_ops->device_release) {
>> +		mutex_lock(&partition->pt_mutex);
>> +		hlist_del(&mshv_dev->device_ptnode);
>> +		mshv_dev->device_ops->device_release(mshv_dev);
>> +		mutex_unlock(&partition->pt_mutex);
>> +	}
>> +
>> +	mshv_partition_put(partition);
>> +	return 0;
>> +}
>> +
>> +static const struct file_operations mshv_device_fops = {
>> +	.owner = THIS_MODULE,
>> +	.unlocked_ioctl = mshv_device_fop_ioctl,
>> +	.release = mshv_device_fop_release,
>> +};
>> +
>> +long mshv_partition_ioctl_create_device(struct mshv_partition *partition,
>> +					void __user *uarg)
>> +{
>> +	long rc;
>> +	struct mshv_create_device devargk;
>> +	struct mshv_device *mshv_dev;
>> +	const struct mshv_device_ops *vfio_ops;
>> +	int type;
>> +
>> +	if (copy_from_user(&devargk, uarg, sizeof(devargk))) {
>> +		rc = -EFAULT;
>> +		goto out;
>> +	}
>> +
>> +	/* At present, only VFIO is supported */
>> +	if (devargk.type != MSHV_DEV_TYPE_VFIO) {
>> +		rc = -ENODEV;
>> +		goto out;
>> +	}
>> +
>> +	if (devargk.flags & MSHV_CREATE_DEVICE_TEST) {
>> +		rc = 0;
>> +		goto out;
>> +	}
>> +
>> +	mshv_dev = kzalloc(sizeof(*mshv_dev), GFP_KERNEL_ACCOUNT);
>> +	if (mshv_dev == NULL) {
>> +		rc = -ENOMEM;
>> +		goto out;
>> +	}
>> +
>> +	vfio_ops = &mshv_vfio_device_ops;
>> +	mshv_dev->device_ops = vfio_ops;
>> +	mshv_dev->device_pt = partition;
>> +
>> +	rc = vfio_ops->device_create(mshv_dev, type);
>> +	if (rc < 0) {
>> +		kfree(mshv_dev);
>> +		goto out;
>> +	}
>> +
>> +	hlist_add_head(&mshv_dev->device_ptnode, &partition->pt_devices);
>> +
>> +	mshv_partition_get(partition);
>> +	rc = anon_inode_getfd(vfio_ops->device_name, &mshv_device_fops,
>> +			      mshv_dev, O_RDWR | O_CLOEXEC);
>> +	if (rc < 0) {
>> +		mshv_partition_put(partition);
>> +		hlist_del(&mshv_dev->device_ptnode);
>> +		vfio_ops->device_release(mshv_dev);
>> +		goto out;
>> +	}
>> +
>> +	devargk.fd = rc;
>> +	rc = 0;
>> +
>> +	if (copy_to_user(uarg, &devargk, sizeof(devargk))) {
> 
> Shouldn't the partition be put here?

No. anon_inode_getfd was successful and so it installed the fd already..
As a result the cleanup will happen in the file op release.

Thanks,
-Mukesh

> Thanks,
> Stanislav
> 
>> +		rc = -EFAULT;
>> +		goto out;
>> +	}
>> +out:
>> +	return rc;
>> +}
>> +
>>   static long
>>   mshv_partition_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>>   {
>> @@ -1587,6 +1710,9 @@ mshv_partition_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>>   	case MSHV_ROOT_HVCALL:
>>   		ret = mshv_ioctl_passthru_hvcall(partition, true, uarg);
>>   		break;
>> +	case MSHV_CREATE_DEVICE:
>> +		ret = mshv_partition_ioctl_create_device(partition, uarg);
>> +		break;
>>   	default:
>>   		ret = -ENOTTY;
>>   	}
>> -- 
>> 2.51.2.vfs.0.1
>>