linux-kernel - Re: [RFC v1 7/8] mshv: implement in-kernel device framework

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Date:   Tue, 3 Aug 2021 22:04:20 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        pasha.tatashin@...een.com, Jonathan Corbet <corbet@....net>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Lillian Grassin-Drake <ligrassi@...rosoft.com>,
        Muminul Islam <muislam@...rosoft.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [RFC v1 7/8] mshv: implement in-kernel device framework

On Wed, Aug 04, 2021 at 12:42:22AM +0530, Praveen Kumar wrote:
> On 09-07-2021 17:13, Wei Liu wrote:
[...]
> > +static long mshv_device_ioctl(struct file *filp, unsigned int ioctl,
> > +			      unsigned long arg)
> > +{
> > +	struct mshv_device *dev = filp->private_data;
> > +
> > +	switch (ioctl) {
> > +	case MSHV_SET_DEVICE_ATTR:
> > +		return mshv_device_ioctl_attr(dev, dev->ops->set_attr, arg);
> > +	case MSHV_GET_DEVICE_ATTR:
> > +		return mshv_device_ioctl_attr(dev, dev->ops->get_attr, arg);
> > +	case MSHV_HAS_DEVICE_ATTR:
> > +		return mshv_device_ioctl_attr(dev, dev->ops->has_attr, arg);
> > +	default:
> > +		if (dev->ops->ioctl)
> > +			return dev->ops->ioctl(dev, ioctl, arg);
> > +
> > +		return -ENOTTY;
> > +	}
> 
> Have seen some static analyzer tool cribbing here of not returning any error.
> If you feel OK, please move the 'return -ENOTTY' down after switch block. Thanks.
> 

Fair point. I will make the change.

> > +}
> > +
[...]
> > +static long
> > +mshv_partition_ioctl_create_device(struct mshv_partition *partition,
> > +	void __user *user_args)
> > +{
> > +	long r;
> > +	struct mshv_create_device tmp, *cd;
> > +	struct mshv_device *dev;
> > +	const struct mshv_device_ops *ops;
> > +	int type;
> > +
> > +	if (copy_from_user(&tmp, user_args, sizeof(tmp))) {
> > +		r = -EFAULT;
> > +		goto out;
> > +	}
> > +
> > +	cd = &tmp;
> > +
> > +	if (cd->type >= ARRAY_SIZE(mshv_device_ops_table)) {
> > +		r = -ENODEV;
> > +		goto out;
> > +	}
> > +
> > +	type = array_index_nospec(cd->type, ARRAY_SIZE(mshv_device_ops_table));
> > +	ops = mshv_device_ops_table[type];
> > +	if (ops == NULL) {
> > +		r = -ENODEV;
> > +		goto out;
> > +	}
> > +
> > +	if (cd->flags & MSHV_CREATE_DEVICE_TEST) {
> > +		r = 0;
> > +		goto out;
> > +	}
> > +
> > +	dev = kzalloc(sizeof(*dev), GFP_KERNEL_ACCOUNT);
> > +	if (!dev) {
> > +		r = -ENOMEM;
> > +		goto out;
> > +	}
> > +
> > +	dev->ops = ops;
> > +	dev->partition = partition;
> > +
> > +	r = ops->create(dev, type);
> > +	if (r < 0) {
> > +		kfree(dev);
> > +		goto out;
> > +	}
> > +
> > +	list_add(&dev->partition_node, &partition->devices);
> > +
> > +	if (ops->init)
> > +		ops->init(dev);
> > +
> > +	mshv_partition_get(partition);
> > +	r = anon_inode_getfd(ops->name, &mshv_device_fops, dev, O_RDWR | O_CLOEXEC);
> > +	if (r < 0) {
> > +		mshv_partition_put_no_destroy(partition);
> > +		list_del(&dev->partition_node);
> > +		ops->destroy(dev);
> 
> I hope ops->destroy will free dev as well ?

Yes. It is clearly written in the preceding comment of that hook. I hope
that's prominent enough.

> 
> > +		goto out;
> > +	}
> > +
> > +	cd->fd = r;
> > +	r = 0;
> > +
> > +	if (copy_to_user(user_args, &tmp, sizeof(tmp))) {
> > +		r = -EFAULT;
> 
> I don't think we will be cleaning up anything ? Or do we need to?

No need. Whatever residuals left will be cleaned up once the VM is
destroyed.

Wei.

> > +		goto out;
> > +	}
> > +out:
> > +	return r;
> > +}
> > +
> 
> Regards,
> 
> ~Praveen.